People that are considered for treatment must undergo an extensive clinical workup, including corneal tomography, computerized  corneal topography , endothelial  microscopy , ultrasound  pachymetry ,  b-scan   sonography ,  keratometry  and biomicroscopy. [ citation needed ]


The technique was first developed in Germany in 1997 by  Theo Seiler  and his team at the  Dresden University of Technology . [ 8 ] [ 9 ]


In Germany, CXL has been used in patients with keratoconus since 1998, [ 8 ]  and in Italy, routine interventions have been successfully performed since 2005. [ 10 ]  The standard (Dresden) CXL protocol with  epithelium  removal, is approved for use throughout Europe.


In the United States, clinical trials commenced only in 2008. Based on three 12-month clinical trials, the  US Food and Drug Administration  approved riboflavin ophthalmic solution and Avedro's KXL system for crosslinking on 18 April 2016, for the treatment of progressive keratoconus, and on 19 July 2016, for corneal ectasia after refractive surgery, making them the first FDA approved treatment for keratoconus and post-LASIK ectasia. [ 3 ] [ 11 ]


Research studying the safety and efficacy of corneal cross-linking is ongoing. [ 4 ] [ 12 ] [ 13 ]


Transepithelial or epithelium-on (epi-on) cross-linking is a technique which was first performed in 2004 in the U.S., [ 14 ]  the corneal epithelium layer is left intact. [ 15 ]  in this technique, because the epithelium is not removed, riboflavin loading requires more time than with epi-off techniques, and may be less effective, as keratoconus progression may be more likely in epi-on procedures. [ 16 ]


Contact lens-assisted cross-linking (CACXL) may be performed for people with corneal stromal thickness between 350 μm to 400 μm after epithelial removal. in this method a pre-corneal riboflavin film, a riboflavin-soaked UV barrier-free  soft contact lens  of negligible power and a pre-contact lens riboflavin film are used to decrease UV irradiance to safe levels at the level of the endothelium. [ 17 ] [ 18 ]


Topography-guided crosslinking relies on an active eye tracker to allow a patterned delivery of UV light. Both the power and pattern can be programmed into the unit based on the topography of the individual's eyes. [ 19 ]


Accelerated crosslinking allows a shorter treatment time by delivering the same energy more quickly, compared to the standard crosslinking procedure, which involves 3 mW of UV-A exposure for 30 minutes. [ 19 ]  Some hospitals are using this accelerated CXL technique delivering a similar amount of UV-A energy in eight to ten minutes, following research showing the cornea may better tolerate this shorter burst of UV-A. [ 20 ] [ 21 ]  However, a recent study using the real-world registry data showed that the standard (Dresden) CXL was associated with better visual and corneal curvature outcomes 5-years post-surgery. [ 12 ]


Corneal transplantation , also known as  corneal grafting , is a  surgical procedure  where a damaged or diseased  cornea  is replaced by  donated corneal tissue  (the graft). When the entire cornea is replaced it is  known as  penetrating keratoplasty  and when only part of the cornea is replaced it is known as  lamellar keratoplasty . Keratoplasty simply means surgery to the cornea. The graft is taken from a recently deceased individual with no known diseases or other factors that may affect the chance of survival of the donated tissue or the health of the recipient.


The cornea is the  transparent  front part of the  eye  that covers the  iris ,  pupil  and  anterior chamber . The surgical procedure is performed by  ophthalmologists , physicians who specialize in eyes, and is often done on an  outpatient  basis. Donors can be of any age, as is shown in the case of  Janis Babson , who donated her eyes after dying at the age of 10. [ 1 ] [ 2 ]  Corneal transplantation is performed when medicines,  keratoconus  conservative surgery and cross-linking can no longer heal the  cornea .


This surgical procedure usually treats corneal blindness, [ 3 ] [ 4 ]  with success rates of at least 41% as of 2021. [ 5 ] [ 6 ] [ 7 ]


Indications include the following:


The risks are similar to other intraocular procedures, but additionally include graft rejection (lifelong), detachment or displacement of lamellar transplants and primary graft failure. Use of immunosuppressants including cyclosporine A, tacrolimus, mycophenolate mofetil, sirolimus, and leflunomide  to prevent graft rejection is increasing but there is insufficient evidence to ascertain which immunosuppressant is better. [ 8 ]  In a Cochrane review which included low to moderate quality evidence, adverse effects were found to be common with systemic mycophenolate mofetil, but less common with topical cyclosporine A or tacrolimus.


There is also a risk of  infection . Since the cornea has no blood vessels (it takes its nutrients from the  aqueous humor ) it heals much more slowly than a cut on the skin. While the  wound  is healing, it is possible that it might become infected by various  microorganisms . This risk is minimized by antibiotic  prophylaxis  (using antibiotic eyedrops, even when no infection exists).


There is a risk of cornea rejection, which occurs in about 10% of cases. [ 9 ]  Graft failure can occur at any time after the cornea has been transplanted, even years or decades later. The causes can vary, though it is usually due to new injury or illness. Treatment can be either medical or surgical, depending on the individual case. An early, technical cause of failure may be an excessively tight stitch  cheesewiring  through the  sclera .


Infectious disease transmission through corneal transplantation is exceedingly rare. [ 10 ]  All corneal grafts are screened for the presence of viruses such as HIV or hepatitis through antibody or nucleic acid testing, and there has never been a reported case of HIV transmission through corneal transplant surgery. [ 11 ]  Prior to the development of reliable HIV testing, many countries instituted  bans on corneal donation by gay men . For example, on 20 May 1994, the United States banned corneal donation by any man who has had sex with another man in the preceding 5 years, even if all HIV testing is negative (a policy which continues to be enforced today). [ 12 ]


On the day of the  surgery , the patient arrives to either a  hospital  or an outpatient surgery center, where the procedure will be performed. The patient is given a brief physical examination by the surgical team and is taken to the  operating room . In the operating room, the patient lies down on an operating table and is either given  general anesthesia , or  local anesthesia  and a  sedative .


With anesthesia induced, the surgical team prepares the eye to be operated on and drapes the face around the eye. An eyelid  speculum  is placed to keep the lids open, and some lubrication is placed on the eye to prevent drying. In children, a metal ring is stitched to the sclera which will provide support of the sclera during the procedure.


In most instances, the person will meet with their ophthalmologist for an examination in the weeks or months preceding the surgery. During the exam, the ophthalmologist will examine the eye and diagnose the condition. The doctor will then discuss the condition with the patient, including the different treatment options available. The doctor will also discuss the risks and benefits of the various options. If the patient elects to proceed with the surgery, the doctor will have the patient sign an  informed consent  form. The doctor might also perform a physical examination and order lab tests, such as blood work,  X-rays , or an  EKG .


The surgery date and time will also be set, and the patient will be told where the surgery will take place. Within the United States, the supply of corneas is sufficient to meet the demand for surgery and research purposes. Therefore, unlike other tissues for transplantation, delays and shortages are not usually an issue. [ 13 ]


A trephine (a circular cutting device), which removes a circular disc of cornea, is used by the surgeon to cut the donor cornea. A second trephine is then used to remove a similar-sized portion of the patient's cornea.  The donor tissue is then sewn in place with sutures.


Antibiotic   eyedrops  are placed, the eye is patched, and the patient is taken to a recovery area while the effects of the anesthesia wear off. The patient typically goes home following this and sees the doctor the following day for the first postoperative appointment.


Lamellar keratoplasty encompasses several techniques which selectively replace diseased layers of the cornea while leaving healthy layers in place.  The chief advantage is improved tectonic integrity of the eye.  Disadvantages include the technically challenging nature of these procedures, which replace portions of a structure only 500  μm  thick, and reduced optical performance of the donor/recipient interface compared to full-thickness keratoplasty.


In this procedure, the anterior layers of the central cornea are removed and replaced with donor tissue.  Endothelial  cells and the Descemets membrane are left in place.  This technique is used in cases of anterior corneal opacifications, scars, and ectatic diseases such as keratoconus.


Endothelial keratoplasty replaces the patient's endothelium with a transplanted disc of posterior stroma/Descemets/endothelium (DSEK) or Descemets/endothelium (DMEK). [ 14 ]


This relatively new procedure has revolutionized treatment of disorders of the innermost layer of the cornea (endothelium). Unlike a full-thickness corneal transplant, the surgery can be performed with one or no sutures.  Patients may recover functional vision in days to weeks, as opposed to up to a year with full thickness transplants. However, an Australian study has shown that despite its benefits, the loss of endothelial cells that maintain transparency is much higher in DSEK compared to a full-thickness corneal transplant. The reason may be greater tissue manipulation during surgery, the study concluded. [ 15 ]


During surgery the patient's corneal endothelium is removed and replaced with donor tissue.  With DSEK, the donor includes a thin layer of stroma, as well as endothelium, and is commonly 100–150 μm thick. With DMEK, only the endothelium is transplanted. In the immediate postoperative period the donor tissue is held in position with an air bubble placed inside the eye (the anterior chamber).  The tissue self-adheres in a short period and the air is adsorbed into the surrounding tissues.


Complications include displacement of the donor tissue requiring repositioning ("refloating").  This is more common with DMEK than DSEK.  Folds in the donor tissue may reduce the quality of vision, requiring repair.  Rejection of the donor tissue may require repeating the procedure.  Gradual reduction in endothelial cell density over time can lead to loss of clarity and require repeating the procedure.


Patients with endothelial transplants frequently achieve best corrected vision in the 20/30 to 20/40 range, although some reach 20/20.  Optical irregularity at the graft/host interface may limit vision below 20/20.


The  Boston keratoprosthesis  is the most widely used synthetic cornea to date with over 900 procedures performed worldwide in 2008. The Boston KPro was developed at the  Massachusetts Eye and Ear  Infirmary under the leadership of Claes Dohlman. [ 16 ] [ further explanation needed ]


In cases where there have been several graft failures or the risk for keratoplasty is high, synthetic corneas can substitute successfully for donor corneas. Such a device contains a peripheral skirt and a transparent central region. These two parts are connected on a molecular level by an  interpenetrating polymer network , made from  poly-2-hydroxyethyl methacrylate  (pHEMA). AlphaCor is a U.S.  FDA -approved type of synthetic cornea measuring 7.0 mm in diameter and 0.5 mm in thickness. The main advantages of synthetic corneas are that they are biocompatible, and the network between the parts and the device prevents complications that could arise at their interface. The probability of retention in one large study was estimated at 62% at 2 years follow-up. [ 17 ]


In a very rare and complex multi-step surgical procedure, employed to help the most disabled patients, a lamina of the person's tooth is grafted into the eye, with an artificial lens installed in the transplanted piece. [ clarification needed ]


The prognosis for visual restoration and maintenance of ocular health with corneal transplants is generally very good.  Risks for failure or guarded prognoses are multifactorial.  The type of transplant, the disease state requiring the procedure, the health of the other parts of the recipient eye and even the health of the donor tissue may all confer a more or less favorable prognosis.


The majority of corneal transplants result in significant improvement in visual function for many years or a lifetime.  In cases of rejection or transplant failure, the surgery can generally be repeated.


Different types of  contact lenses  may be used to delay or eliminate the need for corneal transplantation in corneal disorders.


Diseases that only affect the surface of the cornea can be treated with an operation called  phototherapeutic keratectomy  (PTK). With the precision of an excimer laser and a modulating agent coating the eye, irregularities on the surface can be removed. However, in most of the cases where corneal transplantation is recommended, PTK would not be effective.


In corneal disorders where vision correction is not possible by using contact lenses,  intrastromal corneal ring segments  may be used to flatten the cornea, which is intended to relieve the  nearsightedness  and  astigmatism . In this procedure, an  ophthalmologist  makes an incision in the cornea of the eye, and inserts two crescent or semi-circular shaped ring segments between the layers of the corneal  stroma , one on each side of the  pupil . [ 18 ]  Intrastromal corneal rings were approved in 2004 by the  Food and Drug Administration  for people with keratoconus who cannot adequately correct their vision with glasses or contact lenses. They were approved under the  Humanitarian Device Exemption , [ 19 ] [ 20 ]  which means the manufacturer did not have to demonstrate effectiveness.


Corneal collagen cross-linking  may delay or eliminate the need for corneal transplantation in  keratoconus  and  post-LASIK ectasia . [ 21 ]


Corneal transplant is one of the most common transplant procedures. [ 22 ]   Although approximately 100,000 procedures are performed worldwide each year, some estimates report that 10,000,000 people are affected by various disorders that would benefit from corneal transplantation. [ 23 ]


In Australia, approximately 2,000 grafts are performed each year. [ 22 ]  According to the  NHS Blood and Transplant , over 2,300 corneal transplant procedures are performed each year in the United Kingdom. [ 24 ]  In the one-year period ending 31 March 2006, 2,503 people received corneal transplants in the UK. [ 25 ]


The first cornea transplant was performed in 1905 by  Eduard Zirm  ( Olomouc Eye Clinic , now  Czech Republic ), making it one of the first types of transplant surgery successfully performed. Another pioneer of the operation was  Ramón Castroviejo . Russian eye surgeon  Vladimir Filatov 's attempts at transplanting cornea started with the first try in 1912 and were continued, gradually improving until on 6 May 1931 he successfully grafted a patient using corneal tissue from a deceased person. [ 26 ]  He widely reported another transplant in 1936, disclosing his technique in full detail. [ 27 ]  In 1936, Castroviejo did a first transplantation in an advanced case of  keratoconus , achieving significant improvement in patient's vision. [ 28 ] [ 29 ]


Tudor Thomas , a clinical teacher for the Welsh National School of Medicine, conceived the idea of a donor system for corneal grafts and an eye bank was established in East Grinstead in 1955. [ 30 ]


Advances in  operating microscopes  enabled surgeons to have a more magnified view of the surgical field, while advances in  materials science  enabled them to use  sutures  finer than a human hair.


Instrumental in the success of cornea transplants were the establishment of  eye banks . These are organizations located throughout the world to coordinate the distribution of donated corneas to surgeons, as well as providing eyes for research. Some eye banks also distribute other  anatomical gifts .


Blades are being replaced by high speed lasers in order to make surgical incisions more precise. These improved incisions allow the cornea to heal more quickly and the sutures to be removed sooner. The cornea heals more strongly than with standard blade operations. Not only does this dramatically improve visual recovery and healing, it also allows the possibility for improvement in visual outcomes.


Since 2004, Amnitrans Eyebank in Rotterdam, The Netherlands, provides donor corneas pre-cut for advanced keratoplasty procedures, such as DSEK, DSAEK, FS-DSEK and DMEK. In 2007, Seattle-based  SightLife , one of the leading corneal tissue banks in the world, introduced a process for the preparation of donated corneal tissue using a femtosecond laser. This process is known as custom corneal tissue.


Endothelial keratoplasty (EK) was introduced by Melles et al. in 1998. Today there are two forms of EK: [ 31 ]


Not all patients with diseased corneas are candidates for endothelial keratoplasty.  These procedures correct corneal endothelial failure, but are not able to correct corneal scarring, thinning, or surface irregularity. There is currently limited data on long-term survival of DMEK grafts however the early indications are very positive. An upcoming systematic review will seek to compare the safety and effectiveness of DMEK versus DSAEK in people with corneal failure from  Fuchs' endothelial dystrophy  and  pseudophakic bullous keratopathy . [ 37 ]


There is a  bioengineering  technique that uses stem cells to create corneas or part of corneas that can be transplanted into the eyes. Corneal stem cells are removed from a healthy cornea. They are collected and, through laboratory procedures,  made into five to ten layers of cells that can be stitched into a patient's eye. The stem cells are placed into the area where the damaged cornea tissue has been removed. This is a good alternative for those that cannot gain vision through regular cornea transplants. A new development, announced by the University of Cincinnati Medical School in May 2007, would use bone marrow stem cells to regrow the cornea and its cells. This technique, which proved successful in mouse trials, would be of use to those with inherited genetic degenerative conditions of the cornea, especially if other means like a transplant are not feasible. It works better than a transplant because these stem cells keep their ability to differentiate and replicate, and so keep the disease from recurring, longer and better.


On 25 August 2010, investigators from Canada and Sweden reported results from the first 10 people in the world treated with the biosynthetic corneas. Two years after having the corneas implanted, six of the 10 patients had improved vision. Nine of the 10 experienced cell and nerve regeneration, meaning that corneal cells and nerves grew into the implant. To make the material, the researchers placed a human gene that regulates the natural production of collagen into specially programmed yeast cells. They then molded the resulting material into the shape of a cornea. This research shows the potential for these bioengineered corneas but the outcomes in this study were not nearly as good as those achieved with human donor corneas. This may become an excellent technique, but right now it is still in the prototype stage and not ready for clinical use. The results were published in the journal  Science Translational Medicine . [ 38 ]


A 2013 cost-benefit analysis by the  Lewin Group  for Eye Bank Association of America, estimated an average cost of $16,500 for each corneal transplant. [ 39 ]


Couching  is the earliest documented form of  cataract  surgery.  It involves dislodging the lens of the eye, thus removing the cloudiness caused by the cataract.  Couching was a precursor to  modern cataract surgery  and  pars plana vitrectomy .


Cataract surgery by “couching” (lens depression) is one of the oldest surgical procedures. The technique involves using a sharp instrument to push the cloudy lens to the bottom of the eye. Perhaps this procedure is that which is mentioned in the articles of the  Code of Hammurabi  (ca. 1792–1750 BC) though it is a mere speculation.   Sushruta , an ancient Indian surgeon, described the procedure in “Sushruta Samhita, Uttar Tantra”, an Indian medical treatise (800 BC) (Duke-Elder, 1969; Chan, 2010). From then on the procedure was widespread throughout the world. Evidence shows that couching was widely practiced in China, Europe and Africa. After the 19th century AD, with the development of modern cataract surgery (Intra ocular extraction of lens (1748)), couching fell out of fashion, though it is still used in parts of Asia and Africa. [ citation needed ]


Couching was practised in ancient India and subsequently introduced to other countries by the Indian physician  Sushruta  ( c.  6th century BCE), [ 1 ]  who described it in his work  Sushruta Samhita  ("Compendium of Sushruta"); the work's Uttaratantra section [ a ]  describes an operation in which a curved needle was used to push the opaque "phlegmatic matter" [ b ]  in the eye out of the way of vision. The phlegm was then said to be blown out of the nose. The eye would later be soaked with warm, clarified butter and then bandaged. Here is a translation from the original Sanskrit:


vv. 55–56: Now procedure of surgical operation of  ślaiṣmika liṅganāśa  (cataract) will be described. It should be taken up (for treatment) if the diseased portion in the pupillary region is not shaped like half moon, sweat drop or pearl: not fixed, uneven and thin in the centre, streaked or variegated and is not found painful or reddish.


vv. 57–61ab: In moderate season, after unction and sudation, the patient should be positioned and held firmly while gazing at his nose steadily. Now the wise surgeon leaving two parts of white circle from the black one towards the outer  canthus  should open his eyes properly free from vascular network and then with a barley-tipped rod-like instrument held firmly in hand with middle, index and thumb fingers should puncture the natural hole-like point with effort and confidence not below, above or in sides. The left eye should be punctured with right hand and vice-versa. When punctured properly a drop of fluid comes out and also there is some typical sound.


vv. 61bc–64ab: Just after puncturing, the expert should irrigate the eye with breast-milk and foment it from outside with  vāta -[wind-]alleviating tender leaves, irrespective of  doṣa  [defect] being stable or mobile, holding the instrument properly in position. Then the pupillary circle should be scraped with the tip of the instrument while the patient, closing the nostril of the side opposite to the punctured eye, should blow so that  kapha  [phlegm] located in the region be eliminated.


vv. 64cd–67: When pupillary region becomes clear like cloudless sun and is painless, it should be considered as scraped properly. (If  doṣa  [defect] cannot be eliminated or it reappears, puncturing is repeated after unction and sudation.) When the sights are seen properly the  śalākā  [probe] should be removed slowly, eye anointed with ghee and bandaged. Then the patient should lie down in supine position in a peaceful chamber. He should avoid belching, coughing, sneezing, spitting and shaking during the operation and thereafter should observe the restrictions as after intake of  sneha  [oil].


v. 68: Eye should be washed with  vāta -[wind-]alleviating decoctions after every three days and to eliminate fear of (aggravation of)  vāyu  [wind], it should also be fomented as mentioned before (from outside and mildly).


v. 69: After observing restrictions for ten days in this way, post-operative measures to normalise vision should be employed along with light diet in proper quantity. [ 2 ]


Couching continues to be popular in some developing countries where modern surgery may be difficult to access or where the population may prefer to rely on traditional treatments.  It is commonly practiced in  Sub-Saharan Africa . [ 3 ]   In  Mali  it remains more popular than modern cataract surgery, despite the fact that the cost of both methods is similar, but with much poorer outcome with couching. [ 4 ]   In  Burkina Faso , a majority of patients were unaware of the causes of cataracts and believed it to be due to  fate . [ 3 ]   It is not performed by ophthalmologists, but rather by local healers or " witch doctors ".


A sharp instrument, such as a thorn or needle, is used to pierce the eye either at the edge of the  cornea  or the  sclera , near the  limbus .  The opaque lens is pushed downwards, allowing light to enter the eye.  Once the patients sees shapes or movement, the procedure is stopped.  The patient is left without a lens ( aphakic ), therefore requiring a powerful positive prescription lens to compensate. [ citation needed ]


Couching is a largely unsuccessful technique with abysmal outcomes.  A minority of patients may regain low or moderate visual acuity, but over 70% are left clinically blind with worse than 20/400 vision. [ 4 ]   A  Nigerian  study showed other complications include  secondary glaucoma ,  hyphaema , and  optic atrophy . [ 5 ]   Couching does not compare favourably to modern cataract surgery.


In  ophthalmology ,  cryoextraction  is a form of  intracapsular cataract extraction  in which a  cryoextractor , a special type of  cryoprobe , is used to freeze the  crystalline lens  and pull it intact from the  eye . [ 1 ]  Dr.  Charles Kelman  is credited with pioneering this surgical method in 1962. It can also be used in the treatment of orbital tumors. [ 2 ]


Cyclodestruction  or  cycloablation  is a surgical procedure done in management of  glaucoma . Cyclodestruction reduces  intraocular pressure  (IOP) of the eye by decreasing production of  aqueous humor  by the destruction of  ciliary body . Until the development of safer and less destructive techniques like micropulse diode cyclophotocoagulation and endocyclophotocoagulation, cyclodestructive surgeries were mainly done in refractory glaucoma, or advanced glaucomatous eyes with poor visual prognosis. [ 1 ]


Cyclodestruction may be done by using  diathermy , penetrating cyclodiathermy,  cryotherapy ,  ultrasound ,  laser  or by  surgical excision. [ 2 ]


Cyclophotocoagulation  (CPC), the most common cyclodestructive procedure is done using laser beam of different wavelengths.  Ruby laser  (693 nm wavelength),  Nd:YAG laser  (1064 nm wavelength) or  diode laser  (810 nm wavelength) can be used to perform CPC. [ 2 ]  Commomon cyclophotocoagulation techniques include transscleral cyclophotocoagulation (TS-CPC), continuous-wave diode cyclophotocoagulation (CW-TSCPC), MicroPulse diode cyclophotocoagulation (MP-TSCPC), endocyclophotocoagulation (ECP) and high-intensity focused ultrasound cyclodestruction (HIFU). Complications are lesser with Trans-scleral diode laser cyclophotocoagulation and Endoscopic diode laser cyclophotocoagulation. [ 3 ] [ 4 ] [ 5 ]


Diode laser with a wavelength of 810 nm is used to perform trans-scleral cyclophotocoagulation. [ 2 ]  In TS-CPC, the laser absorbed by  melanin  of ciliary processes causes  photocoagulation . [ 6 ]  Since it is a painful procedure, TS-CPC is usually performed under  retrobulbar  or  peribulbar   anesthesia . [ 2 ]  Micropulse transscleral diode cyclophotocoagulation (MP-TSCPC), a modified TS-CPC procedure is a more safer procedure. [ 7 ]


Endocyclophotocoagulation (ECP) or endoscopic cyclophotocoagulation using an endoscope allows direct view of the ciliary processes during surgery. [ 8 ]  Compared to TS-CPC,  tissue disruption is lesser with ECP. [ 8 ]


Cyclocryotherapy is done by freezing the  ciliary processes  of the eye. [ 4 ]  In  neovascular glaucoma , cyclocryotherapy is advised when medical control of IOP is not possible. [ 9 ]


Inflammation,  retinal detachment ,  hypotony ,  phthisis bulbi  and sympathetic ophthalmia are some common complications of cyclodestructive procedures. [ 4 ]  Since there is risk of inflammation which lead to hypotony and phthisis bulbi, cyclophotocoagulation must be done with extreme caution in  uveitic  glaucoma. [ 10 ]  Pain,  hyphema  and  iridocyclitis  are possible complications of TS-CPC. [ 2 ]  Fibrin exudates, hyphema, cystoid macular edema and loss of vision are possible complications of ECP.


The first surgical procedures to reduce intraocular pressure of the eye, by decreasing production of aqueous humor, by damaging the ciliary body by diathermy, penetrating cyclodiathermy or surgical excision was done in the early twentieth century. [ 1 ]  Cyclodestruction by diathermy was first performed by Weve in 1933. [ 11 ]  In 1949, Berens et al. described cyclo-electrolysis. [ 11 ]  Cyclocryotherapy was first described by Bietti in 1950. [ 12 ]  Cyclodestruction by cyclophotocoagulation was first performed by Beckman et al., in 1972, using a ruby laser. [ 13 ]  ECP was developed by Martin Uram in 1992. [ 14 ]


Descemet membrane endothelial keratoplasty  ( DMEK ) is a method of  corneal transplantation  that involves the removal of a thin sheet of tissue from the posterior (innermost) side of a person's cornea to replace it with the two posterior (innermost) layers of corneal tissue from a donor's eyeball.


The two exchanged corneal layers are the  Descemet's membrane  and the  corneal endothelium . [ 1 ]  The person's corneal tissue is gently excised, peeled off, and replaced with the donor tissue via small 'clear corneal incisions' (small corneal incisions just anterior to the  corneal limbus . The donor tissue is  tamponaded  against the person's exposed posterior corneal  stroma  by injecting a small air bubble into the  anterior chamber . To ensure the air tamponade is effective, people must maintain such a posture that they look up at the ceiling during recovery until the air bubble has fully resorbed. [ 1 ] [ 2 ]


Indications for DMEK include: [ 3 ]


A minor variation to DMEK is the Descemet Membrane Automated Endothelial Keratoplasty (DMAEK), which involves automated donor tissue preparation using a microkeratome or  femtosecond laser . [ 4 ]


Enucleation  is the removal of the eye that leaves the  eye muscles  and remaining orbital contents intact. This type of  ocular surgery  is indicated for a number of  ocular tumors , in eyes that have sustained severe trauma, and in eyes that are otherwise blind and painful. [ 1 ]


Self-enucleation  or  auto-enucleation  ( oedipism ) and other forms of serious self-inflicted eye injury are an extremely rare form of severe  self-harm  that usually results from mental illnesses involving acute  psychosis . [ 2 ]  The name comes from  Oedipus  of Greek mythology, who gouged out his own eyes. [ 3 ]


There are three types of eye removal: [ 4 ]


Removal of the eye by enucleation or evisceration can relieve pain and minimize further risk to life and well-being of an individual with the above noted conditions. In addition, procedures to remove the eye should address the resultant appearance of the orbit. Orbital implants and ocular prostheses are used by the surgeon to restore a more natural appearance. [ 5 ]


An orbital implant is placed after removal of the eye to restore volume to the eye socket and enhance movement or motility of an ocular prosthesis and eyelids. [ 5 ]  The eyeball is a slightly elongated sphere with a diameter of approximately 24 millimetres. [ 6 ]   To avoid a sunken appearance to the eye socket, an implant approximating this volume can be placed into the space of the removed eye, secured, and covered with  Tenon's capsule  and  conjunctiva . [ 7 ]  Implants can be made of many materials with the most common being  hydroxylapatite , metal alloy, [ 8 ]  acrylic, or glass. [ 9 ]


Later, once the conjunctiva have healed and post-operative swelling has subsided, an  ocular prosthesis  can be placed to provide the appearance of a natural eye. [ 5 ]  The prosthesis is fabricated by an  ocularist . [ 10 ]   Its form is that of a cupped disc so that it can fit comfortably in the pocket behind the eyelids overlying the conjunctiva that covers the orbital implant. [ 10 ]  The external portion of the ocular prosthesis is painted and finished to mimic a natural eye color, shape and luster. [ 8 ]  It can be removed and cleaned periodically by the individual or a care giver. [ 8 ]


The two part system of orbital implant and ocular prosthesis provides a stable, and well tolerated aesthetic restoration of the eye socket. [ 8 ]  Although vision is not restored by removal of the eye with placement of an orbital implant and ocular prosthesis, a natural appearance can result. [ 5 ]  The implant, along with the attached, visible ocular prosthesis, can be moved by intact extraocular muscles that will track or move simultaneously with the other eye. The eyelids are able to move and blink over the prosthesis as well. [ 10 ]


An  evisceration  is the removal of the  eye 's contents, leaving the  scleral  shell and  extraocular muscles  intact. [ 1 ] [ 2 ]  The procedure is usually performed to reduce pain or improve  cosmesis  in a  blind  eye, as in cases of  endophthalmitis  unresponsive to  antibiotics . [ 1 ] [ 2 ]  An  ocular prosthetic  can be fitted over the eviscerated eye in order to improve cosmesis. [ 3 ]


Either  general  or  local anesthetics  may be used during eviscerations, with antibiotics and  anti-inflammatory  agents injected  intravenously . [ 4 ]


Excimer laser trabeculostomy  (ELT) is a procedure to create holes in the  trabecular meshwork  to reduce  intraocular pressure . It uses a  XeCl  308 nm  excimer laser . [ 1 ]  It is considered a  minimally invasive glaucoma surgeries , and was first described in 1987 by Michael Berlin. [ 2 ]


Alternative treatments for glaucoma include mechanical drilling, thermal lasers, thermal cauterisation, and tube implants. However, these approaches typically disrupt the eye tissue enough to cause  inflammation  which often outweighs the benefit of the procedure. [ 1 ]  Excimer laser trabeculostomy uses  cold lasers  which reduces tissue  fibrosis  otherwise caused by excimer lasers. A 2020 review of 8 studies found the procedure reduced intraocular pressure by 20-40% and generally had favourable outcomes for reducing glaucoma medication needs. [ 3 ]


Eye transplantation  is the  transplantation  of the  globe  of the human eye from a donor to a recipient.


Research efforts in whole eye transplantation (WET) are focused on its application in living human recipients, still some obstacles need to be addressed. Apart from the surgical and neurological considerations, there are key ethical concerns such as patients' perceptions and desires for both nonvision-restoring WET and vision-restoring WET, risks and benefits compared to  prosthetic  alternatives, psychosocial considerations for potential recipients regarding personal identity related to the donor's eyes, public perceptions of whole-eye donation, implications for  corneal transplantation  eligibility of the donor's eyes, consent for whole-eye donation, and establishment of ethical mechanisms for allocation and distribution of WET. With limited studies available on this topic since the first vascularized composite allotransplantation (VCA) [ 1 ] [ 2 ] [ 3 ]  took place in 1998, the understanding of WET is informed by a few studies with limitations. For example,  amphibian  regeneration cannot directly apply to humans. Ocular transplants may offer a viable option for restoring form in patients undergoing facial transplantation with enucleated orbits. [ 4 ]


In 1885, the  Revue générale d'ophtalmologie  reported that the  staphylomatous  and  buphthalmic  eye of a 17-year-old girl had been replaced by the eye of a  rabbit  by a Dr. Chibret. [ 5 ] [ 6 ]  The operation failed after 15 days due to a lack of effective  immunosuppression . [ 6 ]


In 1969, Conrad Moore of the  Texas Medical Center  claimed that he had carried out the transplantation of a whole eye, but he subsequently  retracted  his claim. [ 7 ]


In November 2023, surgeons at  NYU Langone Health  announced the first successful eye transplantation, [ 8 ]  which was carried out as part of a partial  face transplant  in an operation that took 21 hours. [ 8 ]  The recipient, Aaron James, had lost the left side of his face with his eye, nose and mouth in a  high-voltage power line  accident. [ 8 ]   Reuters  reported that the transplanted eye has "well-functioning blood vessels and a promising-looking retina". [ 8 ]  The eye is not using the optic nerve to communicate with the brain, and James has not regained sight through the eye. [ 8 ]   Adult stem cells  have been harvested from his bone marrow and been injected into the optic nerve. [ 8 ]  The lead surgeon, Eduardo D. Rodriguez, said that "If some form of vision restoration occurred, it would be wonderful, but ... the goal was for us to perform the technical operation". [ 8 ]


Eyelid revision   is a procedure that involves correcting or addressing any issues that have arisen from a previous  eyelid surgery . The surgery is more difficult to perform and is more complicated than an initial eyelid revision surgery, since the site of the procedure has been operated on before. The reasons for eyelid revision surgeries include contour abnormalities, asymmetry and unusually high eyelid height. [ 1 ]  The procedure is known to have more complications and issues than initial eyelid surgeries due to the presence of excess scar tissue at the surgery site.


Contour abnormalities are also a common cause of eyelid revision surgery. Contour abnormalities are often the result of poor wound closure during the procedure. [ citation needed ]


One of the most frequent complications that arise from an initial  eyelid surgery  is asymmetry, which are often a result of poor markings by the surgeon prior to operation. [ citation needed ]


Unusually high eyelid heights can make the results of an original eyelid revision procedure appear unnatural.  Thus, an initial  blepharoplasty  may need revision if there is an unusually high eyelid height that is formed.


One of the most troublesome complications of initial  eyelid surgery  is the surgeon discovering the patient has  ptosis  or a "drooping" eyelid after the surgery has been performed.  It is also possible for a patient to develop ptosis as a result of an initial eyelid surgery operation. Both require eyelid revision surgeries. Since ptosis patients need correction of delicate anatomical tissues and structures, eyelid revision surgery on ptosis patients is considered one of the more difficult surgical procedures to perform. [ 2 ] [ 3 ]


Glaucoma  is a group of diseases affecting the  optic nerve  that results in  vision loss  and is frequently characterized by raised  intraocular pressure  (IOP). There are many glaucoma surgeries, and variations or combinations of those surgeries, that facilitate the escape of excess  aqueous humor  from the eye to lower intraocular pressure, and a few that lower IOP by decreasing the production of aqueous humor.


A  trabeculoplasty  is a modification of the  trabecular meshwork .  Laser trabeculoplasty  (LTP) is the application of a laser beam to burn areas of the trabecular meshwork, located near the base of the iris, to increase fluid outflow. LTP is used in the treatment of various open-angle glaucomas. [ 1 ]  The two types of laser trabeculoplasty are  argon laser trabeculoplasty  (ALT) and  selective laser trabeculoplasty  (SLT). As its name suggests, argon laser trabeculoplasty uses an  argon laser  to create tiny burns on the trabecular meshwork. [ 2 ]  Selective laser trabeculoplasty is newer technology that uses a  Nd:YAG laser  to target specific cells within the trabecular meshwork and create less thermal damage than ALT. [ 3 ] [ 4 ]  SLT shows promise as a long-term treatment. [ 5 ]  In SLT a laser is used to selectively target the melanocytes in the trabecular meshwork. Though the mechanism by which SLT functions is not well understood, it has been shown in trials to be as effective as the older ALT. However, because SLT is performed using a laser with much lower power than ALT, it does not appear to affect the structure of the trabecular meshwork (based on electron microscopy) to the same extent, so retreatment may be possible if the effects from the original treatment should begin to wear off, although this has not been proven in clinical studies. ALT is repeatable to some extent with measurable results possible. [ citation needed ]


An  iridotomy  involves making puncture-like openings through the  iris  without the removal of iris tissue. Performed either with standard surgical instruments or a laser, it is typically used to decrease intraocular pressure in patients with angle-closure glaucoma. A  laser peripheral iridotomy  (LPI) is the application of a laser beam to selectively burn a hole through the iris near its base. LPI may be performed with either an argon laser or Nd:YAG laser. [ 6 ] [ 7 ]


There is currently no sufficient evidence to show any benefit on the use of iridotomy versus no iridotomy to slow down visual field loss. This is based on analysing four studies with a sample of 3,086 eyes of 1,543 participants; iridotomy seems to improve gonioscopic findings, but does not show to be clinically significant. [ 8 ]


An  iridectomy , also known as a  corectomy  or  surgical iridectomy , involves the removal of a portion of iris tissue. [ 9 ] [ 10 ]  A basal iridectomy is the removal of iris tissue from the far periphery, near the iris root; a peripheral iridectomy is the removal of iris tissue at the periphery; and a sector iridectomy is the removal of a wedge-shaped section of iris that extends from the pupil margin to the iris root, leaving a keyhole-shaped pupil.


Clear lens extraction , a surgical procedure in which clear  lens  of the human eye is removed, may be used to reduce intraocular pressure in primary angle closure glaucoma. [ 11 ]  A study found that CLE is even more effective than laser peripheral  iridotomy  in patients with angle closure glaucoma. [ 12 ] [ 13 ]


Filtering surgeries are the mainstay of surgical treatment to control intraocular pressure. [ 14 ]  An  anterior sclerotomy  or  sclerostomy  is used to gain access to the inner layers of the eye [ 15 ] [ 16 ]  in order to create a drainage channel from the anterior chamber to the external surface of the eye under the conjunctiva, allowing aqueous to seep into a  bleb  from which it is slowly absorbed. Filtering procedures are typically divided into either penetrating or non-penetrating types depending upon whether an intraoperative entry into the anterior chamber occurs. [ 17 ] [ 18 ]


Penetrating filtering surgeries are further subdivided into guarded filtering procedures, also known as protected, subscleral, or partial thickness filtering procedures (in which the surgeon sutures a scleral flap over the sclerostomy site [ 19 ] ), and full thickness procedures. [ 20 ]   Trabeculectomy  is a guarded filtering procedure that removes of part of the trabecular meshwork. [ 21 ] [ 22 ]  Full thickness procedures include sclerectomy, posterior lip sclerectomy (in which the surgeon completely excises the sclera on the area of the sclerostomy [ 19 ] ), trephination, thermal sclerostomy (Scheie procedure), iridenclesis, and sclerostomy (including conventional sclerostomy and enzymatic sclerostomy). [ 18 ] [ 23 ]


Anterior chamber paracentesis  is a penetrating surgical procedure done to reduce intraocular pressure of the eye. [ 24 ]


Non-penetrating filtering surgeries do not penetrate or enter the eye's  anterior chamber . [ 25 ] [ 26 ]  There are two types of non-penetrating surgeries: Bleb-forming and viscocanalostomy. [ 27 ] [ 28 ]  Bleb forming procedures include ab externo trabeculectomy and deep sclerectomy. [ 28 ]  Ab externo trabeculectomy (AET) involves cutting from outside the eye inward to reach  Schlemm's canal , the trabecular meshwork, and the anterior chamber. Also known as non-penetrating trabeculectomy (NPT), it is an ab externo (from the outside), major ocular procedure in which Schlemm's canal is surgically exposed by making a large and very deep scleral flap. The inner wall of Schlemm's canal is stripped off after surgically exposing the canal. Deep sclerectomy, also known as nonpenetrating deep sclerectomy (PDS) or nonpenetrating trabeculectomy, is a filtering surgery where the internal wall of Schlemm's canal is excised, allowing subconjunctival filtration without actually entering the anterior chamber. [ 29 ]  In order to prevent wound adhesion after deep scleral excision and maintain good filtering results, it is sometimes performed with a variety of biocompatible spacers or devices, such as the Aquaflow collagen wick, [ 30 ]  ologen Collagen Matrix, [ 31 ] [ 32 ] [ 33 ]  or Xenoplast glaucoma implant. [ 34 ]


Viscocanalostomy  is also an ab externo, major ocular procedure in which Schlemm's canal is surgically exposed by making a large and very deep scleral flap. In the VC procedure, Schlemm's canal is cannulated and viscoelastic substance injected (which dilates Schlemm's canal and the aqueous collector channels).


Surgical adjuvants
Where wound modulation is needed to prevent closure of surgically created drainage channels, adjuvants such as the ologen collagen matrix implants may be used to facilitate healthy tissue regeneration. Scar formation at the site of excision or operation may block aqueous humor circulation, while healthy tissue regeneration will keep newly created drainage channels functional. [ 35 ] [ 36 ] [ 37 ] [ 38 ]


Goniotomy  and  trabeculotomy  are similar simple and directed techniques of microsurgical dissection with mechanical disruption of the trabecular meshwork. [ 39 ] [ 40 ]  Goniotomy procedures include surgical goniotomy and laser goniotomy. A surgical goniotomy involves cutting the fibers of the trabecular meshwork to allow aqueous fluid to flow more freely from the eye. [ 41 ] [ 42 ] [ 43 ]  Laser goniotomy is also known as goniophotoablation and laser trabecular ablation . In many patients with congenital glaucoma, the cornea is not clear enough to visualize the anterior chamber angle. Although an endoscopic goniotomy, which employs an endoscope to view the anterior chamber angle, may be performed, [ 44 ]  a trabeculotomy which accesses the angle from the exterior surface of the eye, thereby eliminating the need for a clear cornea, is usually preferred in these instances. A specially designed probe is used to tear through the trabecular meshwork to open it and allow fluid flow. [ 41 ] [ 45 ]


Tube-shunt surgery  or  drainage implant surgery  involves the placement of a tube or  glaucoma valves  to facilitate aqueous outflow from the anterior chamber. [ 41 ] [ 46 ] [ 47 ]  Trabeculopuncture uses a Q switched Nd:YAG laser to punch small holes in the trabecular meshwork. [ 48 ] [ 49 ]   Goniocurretage  is an "ab interno" (from the inside) procedure that used an instrument "to scrape pathologically altered trabecular meshwork off the scleral sulcus". [ 14 ]  A surgical  cyclodialysis  is a rarely used procedure that aims to separate the ciliary body from the sclera to form a communication between the suprachoroidal space and the anterior chamber. [ 10 ]  A  cyclogoniotomy  is a surgical procedure for producing a cyclodialysis, in which the ciliary body is cut from its attachment at the scleral spur under gonioscopic control. [ 10 ]


A  ciliarotomy  is a surgical division of the ciliary zone in the treatment of glaucoma. [ 10 ] [ 50 ]


Canaloplasty  is a nonpenetrating procedure utilizing microcatheter technology. To perform a canaloplasty, an incision is made into the eye to gain access to Schlemm's canal in a similar fashion to a viscocanalostomy. A microcatheter will circumnavigate the canal around the iris, enlarging the main drainage channel and its smaller collector channels through the injection of a sterile, gel-like material called viscoelastic. The catheter is then removed and a suture is placed within the canal and tightened. By opening the canal, the pressure inside the eye can then be relieved. Canaloplasty has two main advantages of over more traditional glaucoma surgeries. The first of these advantages is an improved safety profile over trabeculectomy. As canaloplasty does not require the creation of a bleb, significant long-term risks such as infection and hypotony (extremely low eye pressure) are avoided. The second main advantage is that when combined with cataract surgery, the IOP is reduced even further than when done alone. [ 51 ]
Long term (three year) results have been published both in the US [ 51 ]  and Europe [ 52 ]  demonstrating a significant and sustained reduction in both eye pressure and the number of glaucoma medications required for glaucoma control.


Certain cells within the eye's  ciliary body  produce aqueous humor. A ciliary destructive or cyclodestructive procedure is one that aims to destroy those cells in order to reduce intraocular pressure. [ 53 ]


Cyclocryotherapy , or cyclocryopexy, uses a freezing probe. [ 54 ]   Cyclophotocoagulation , also known as transscleral cyclophotocoagulation, ciliary body ablation, [ 41 ]  cyclophotoablation, [ 55 ]  and cyclophototherapy, [ 40 ]  uses a laser. [ 56 ] [1]   Cyclodiathermy  uses heat generated from a high frequency  alternating electric current  passed through the tissue, [ 10 ]  while  cycloelectrolysis  uses the chemical action caused by a  direct current . [ 10 ]


A systematic review seeking to assess the safety and effectiveness of diode transscleral cyclophotocoagulation found one study in Ghana comparing patients who received low-energy versus high-energy variations of the procedure to treat glaucoma. [ 57 ]  Overall, the review found that 47% of eyes treated with transscleral cytophotocoagulation saw an IOP decrease of at least 20%. [ 57 ]  There were no differences between the low-energy and high-energy variations of the procedure in all reported outcomes, such as IOP control, and number of medications used after treatment. [ 57 ]  Another  Cochrane Systematic Review  explored whether cyclodestructive procedures are better than other glaucoma treatments for the treatment of refractory glaucoma; however, the evidence was inconclusive. [ 58 ]


In  ophthalmology ,  glued intraocular lens [ 1 ]  or  glued IOL  is a  surgical technique  for implantation, with the use of biological glue, of a  posterior chamber  IOL ( intraocular lens ) in  eyes  with deficient or absent  posterior capsules . A quick-acting surgical  fibrin sealant  derived from human  blood plasma , [ 2 ] [ 3 ]  with both  hemostatic  and adhesive properties, is used.


In 1997, Maggi and Maggi were the first to report the sutureless  scleral  fixation of a special IOL. The sutureless intrascleral fixation of a  posterior chamber  IOL was first described by Gabor Scharioth. [ 4 ] [ 5 ]  This technique was further modified by making scleral flaps and creating scleral pockets for tucking the haptics. The flaps are then reattached to the bed with the help of glue.


On 14 December 2007, the first glued  intraocular lens  (IOL) surgery was performed, at  Dr. Agarwal's Eye Hospital  in  Chennai , India. This new surgical procedure was invented and performed by  Amar Agarwal . Subsequently, the first child on whom a glued IOL surgery was performed was a patient who had a history of injury to her right eye 3 months before, while bursting crackers. She underwent emergency surgery for lens removal due to severe injury to the lens and received a sutured IOL, which was specific for such cases. After 1 month, when the child came for follow up, it was found that there was a decenteration of the IOL. The parents had noted the child's difficulty in performing activities using the right eye. Under  general anaesthesia , Agarwal removed the already existing IOL and placed a new IOL using the Glued IOL technique.


Glued IOL surgery can be done both as a primary and as a secondary procedure in cases where the lens capsule is deficient or absent. As a primary procedure it can be done in all cases of  intraoperative  posterior capsule rupture. It can also be done in all cases of  subluxation  or dislocation of the lens, such as in  Marfan syndrome , traumatic dislocation of lens, etc. As a secondary procedure it can be done in all the  aphakic  cases or as a part of an IOL exchange, following an anterior chamber IOL, or  subluxated  or dislocated IOL.


Fibrin glue has been used previously, in various medical specialties, as a  hemostatic  agent to arrest bleeding, seal tissues, and as an adjunct to wound healing. It is available in a sealed pack that contains freeze-dried human  fibrinogen  (20 mg/0.5 ml), freeze-dried human  thrombin  (250  IU /0.5 ml),  aprotinin  solution (1,500 KIU in 0.5 ml), one  ampoule  of sterile water, four 21-gauge needles, two 20-gauge blunt application needles, an applicator with two mixing chambers, and one plunger guide.


Preparation of glue: The vials are placed in a water bath which is preheated to 37 degrees for 2 to 3 minutes. 0.5 cc of distilled water is then added to the  thrombin   vial , and the  aprotinin  is mixed with  fibrinogen . Each component is then placed in a separate  syringe  with a  26-gauge  needle attached.


The glued IOL technique consists of making two partial-thickness, approximately 2.5 mm by 2.5 mm, scleral flaps exactly 180° apart, followed by a sclerotomy with a 20-gauge needle 1 mm from the limbus. A 23-gauge vitrectomy cutter is introduced from the sclerotomy site, and a thorough  vitrectomy  is done to remove all the vitreous tractions. A corneal tunnel is fashioned, then a 23-gauge glued-IOL forceps is passed through the sclerotomy site, and the tip of the leading haptic of the IOL is grasped, which is then externalized and brought out onto the ocular surface (Fig 3). Similarly the trailing haptic is then externalized using the "handshake technique". Scleral pockets are made at the edge of the flap with a 26-gauge needle just parallel to the sclerotomy site, into which the two haptics are then tucked for additional stability (Fig 4). The scleral flaps are then glued back into place using biological glue. The IOLs that can be used are the three-piece foldable IOLs with slightly firm haptics, or a three-piece non-foldable IOL. The glue is then used to seal the  conjunctival  closure.


The concept of performing a "vertical glued IOL" was first suggested by Jeevan Ladi. The vertical corneal diameter is always less than the horizontal diameter. In cases of large eyes, the least corneal diameter (i.e. at 6 o'clock and 9 o'clock) along the vertical axis can be chosen for making the scleral flaps. The IOLs currently available in the market are 13 mm in length. Choosing the least corneal diameter allows for extra length of the haptic available for tucking, and so gives extra stability.


Advantages:


According to some studies by Steven Safran, it is essential to state that the diameter of the ciliary sulcus and the corneal horizontal white-white diameter may not co-relate exactly; and it has been suggested that the surgeon can go ahead with horizontal placement of haptics rather than orienting them vertically. [ 6 ]


No-Assistant technique  – This technique works on the principle of vector forces and was first performed by Priya Narang. [ 7 ] [ 8 ] [ 9 ]  In this technique, after the externalization of the leading haptic, the trailing haptic is flexed beyond the pupillary plane, towards the 6 o'clock position. This reverses the direction of vector forces and causes the leading haptic to extrude more from the previous sclerotomy site, thereby preventing haptic slippage and its subsequent complications.


Plugging Silicon Tires of Iris Hooks  – This technique was developed by George Beiko and Roger Steinert, wherein the silicon tires of the iris hooks are plugged to the leading haptic, to prevent its accidental slippage. [ 10 ]  Steven Safran developed the micro-bulldog technique for the same purpose.


Y-Fixation technique  – This technique was developed by Ohta Toshihiko, et al., wherein a Y-shaped incision is made, in the sclera, that eliminates the need to make a scleral flap. [ 11 ]
Mckee Yuri, Francis Price, et al., modified the scleral flap-making by lifting only two edges of the flap and keeping the flap adherent at the point of haptic enclavation. [ 12 ]


This technique is used for easy externalisation of haptics (Fig 5 and 6), especially for externalisation of the trailing haptic and in cases of there being small pupil. [ 13 ]  Two glued IOL forceps are needed for this technique. The haptic is held with one forceps, which is introduced from the corneal tunnel, and the other forceps is introduced from the sclerotomy site. The tip of the haptic is then traced and is caught followed by externalisation from the sclerotomy site. Visualization of the tip of the haptic becomes very difficult in cases of a small pupil. Although iris hooks can be used, the handshake technique simplifies the procedure. The exteriorization of the haptics is a key step in the glued IOL surgery. Since the surgeon is maneuvering with both hands simultaneously, one hand injecting the IOL while the other grasps and exteriorizes the haptics, he/she needs to be familiar with the handshake technique as a means of transferring the haptic from one hand to the other.


If one of the haptics is not caught or if it is released accidentally after being grasped, the situation can be easily resolved using this technique. It utilizes two glued IOL forceps, one of which holds the haptic. Depending on ease of access, the other forceps is introduced through the opposite sclerotomy or through the side-port. The haptic is transferred from the first to the second forceps, such that the first forceps becomes free. It is essential to hold the haptic at its tip before exteriorizing it so that it doesn't snag on the sclerotomy while being brought out. For this reason, this handshake transfer of the haptic between the two glued IOL forceps is continued until the tip of the haptic is caught by the forceps on the side to which the haptic is to be exteriorized. This technique thus allows easy intra-ocular maneuvering of the entire haptic or IOL within a closed globe system.


Multifocal IOLs allow for good vision at a range of distances. Monofocal intraocular lenses, which are commonly available, give clear far or near point-of-focus, but are limited to only one focal point.  Multifocal intraocular lenses  are designed to avoid the need for glasses by providing two or more points of focus.


Multifocal  glued IOL procedures have been done with the ReZoom (Abbott Medical Optics), and Tecnis ( Advanced Medical Optics  (AMO)) IOLs. This makes it possible to offer the accommodative IOL advantage even to patients with an absent capsule. The modified  Prolene   polyvinylidene fluoride  haptic in these IOLs helps them in being more stiff as well as having superior structural memory. Sutured scleral-fixated IOLs in pediatric eyes have been known to lead to problems.


These intraocular lenses are intended to be placed in the capsular bag. Until recently, it was difficult to provide multifocality for patients who had complicated cataract surgeries and who lacked normal capsules.  Aphakia  with deficient capsule has been a limitation for obtaining multifocality. Now multifocality is possible even in complicated cataract surgeries by the Multifocal Glued IOL procedure, where multifocal IOL implantation can be done even in eyes with large posterior capsular rupture (PCR) and aphakias with deficient posterior capsule.


Good results are reported for multiple complicated  pediatric  glued IOL situations, such as for  homocystinuria  with  subluxation ,  aniridia  with cataractous  subluxated  lens, and  Weill-Marchesani syndrome  with  microspherophakia  and  glaucoma . In dislocated posterior chamber  PMMA  IOL, the same IOL can be repositioned, thereby reducing the need for further manipulation.


This glued IOL technique can be used in cases in which there is  aphakia  with  aniridia  (Fig 7 A and B). In such cases one can use an  aniridia  IOL, which has an artificial iris. [ 14 ]


This procedure combines two techniques: Glued IOL and  IOL Scaffold . [ 15 ] [ 16 ]  In this technique, a glued IOL procedure is initially performed, followed by an IOL Scaffold procedure. [ 17 ]  This technique is specially effective in cases with deficient posterior capsule support and sulcus or iris support. This technique is also applicable for managing a traumatic subluxated lens and Soemmering ring. [ 18 ]


This is a combination of  Pre-Descemet's endothelial keratoplasty  (PDEK) [ 19 ]  and glued IOL (Fig 8). This combined procedure helps to perform two procedures simultaneously, thereby limiting the number of the patient's post-operative hospital visits. PDEK is a kind of endothelial keratoplasty (corneal or eye transplantation), where the Pre-Descemet's layer (PDL), along with Descemet's membrane (DM) and endothelium, is transplanted.
The normal cornea has from the front to the back the following layers:


For the human eye to see, the cornea, the front window of the eye, should be transparent. For that to happen, the inside corneal layer, the endothelium, pumps water from the cornea so that the cornea remains transparent and light can pass into the eye. If the endothelium is bad, the cornea retains a lot of water and becomes damaged, which is called Bullous  Keratoplasty . Thus PDEK helps in replacing the non-functional endothelium.


On 4 September 2013,  Amar Agarwal , in collaboration with  Harminder Dua , performed the first PDEK surgery technique and demonstrated the significance of the Pre-Descemets layer in corneal transplantation. The initial surgery was performed for pseudophakic bullous keratopathy. Though donor eyes of all age groups were used in the initial PDEK cases, there was a marked difference in eyes with young donor corneas, which resulted in better corneal clarity and visual outcome. This paved the way for the difference of PDEK using young donors and the importance of the endothelial viability.
Glued IOL can also be performed with various other  corneal transplantation  / keratoplasty procedures, such as Descemet's membrane endothelial keratoplasty (DMEK), Descemet's stripping endothelial keratoplasty (DSEK), and Penetrating keratoplasty (PK).


This glued IOL technique would be useful in many clinical situations in which scleral-fixated IOLs are indicated, such as luxated IOL, dislocated IOL, zonulopathy, or secondary IOL implantation. In a case with a dislocated posterior chamber, such as  PMMA  IOL, the same IOL can be repositioned, thereby reducing the need for further manipulation. Externalization of the greater part of the haptics along the curvature stabilizes the axial positioning of the IOL and thereby prevents any IOL tilt.


There is less incidence of uveitis-glaucoma-hyphema syndrome in a fibrin glue–assisted IOL implantation, as compared with a sutured scleral-fixated IOL implantation. In the former, the IOL is well stabilized and stuck onto the scleral bed, and thereby has decreased intraocular mobility; in the latter, there is increased possibility of IOL movement or persistent rub over the ciliary body. Visually significant complications due to late subluxation, which has been known to occur in sutured scleral-fixated IOLs, may also be prevented, as sutures are avoided in this technique. Moreover, the frequent complications of secondary IOL implantation—such as  secondary glaucoma , cystoid macular edema, or bullous keratopathy—were not seen in any patients. Another important advantage of this technique is the prevention of suture-related complications, such as suture erosion, suture knot exposure, or dislocation of IOL after suture disintegration or broken suture.


The other advantages of this technique are the rapidity and ease of surgery. The technique eliminates tying the difficult-to-handle 10-0 Prolene suture to the IOL haptic eyelets, the time required to ensure good centration before tying down the knots, and the time required for suturing scleral flaps and closing the conjunctiva, thus significantly reducing total time in surgery. It is also easier and does not require much surgical expertise to use the 25-gauge forceps to grasp and exteriorize the haptic. Fibrin glue takes only 20 seconds to act in the scleral bed, and it helps in adhesion and  hemostasis . Fibrin glue has been shown to provide airtight closure, and by the time the fibrin starts degrading, surgical adhesions would have already occurred in the scleral bed.


A  Gundersen flap , also known as  Gundersen's flap ,  Gundersen's conjunctival flap , or  conjunctivoplasty , and often misspelled  Gunderson , is a  surgical  procedure for correcting  corneal disease . It involves excising a damaged section of cornea, and replacing it with a section (or "flap") of the patient's own  conjunctiva . [ 1 ]


It is named for Trygve Gundersen (1902 – February 24, 1987), an American  ophthalmologist  of Scandinavian descent, who first described the procedure in 1958 at the  Massachusetts Eye and Ear Infirmary . [ 2 ]


The  Harada–Ito procedure  is an  eye muscle  operation designed to improve the  excyclotorsion  experienced by some patients with  cranial nerve IV palsy .   In this procedure, the  superior oblique  tendon is split, and the anterior fibers – the fibers most responsible for  incyclotorsion  – are moved anteriorly and laterally.  This selectively stretches and tightens these fibers, enhancing the incyclotorsion power of the superior oblique.


The most common indication for the Harada–Ito procedure is bilateral acquired cranial nerve IV palsy following closed  head trauma  (particularly automobile accidents).  In this clinical situation the vertical imbalance is often less symptomatically bothersome to the patient than the induced excyclotorsion.  Affected patients have a particularly annoying type of double vision ( diplopia ), wherein the images are twisted (excyclotorted).


Patients with cranial nerve IV palsy whose complaints are not specifically limited to torsional diplopia, but instead also have significant vertical diplopia, are not good candidates for a Harada–Ito procedure.  Instead, a recession of the  inferior oblique  muscle, or another  strabismus  operation may be indicated.


Cataract surgery  has a long history in Europe, Asia, and Africa. It is one of the most common and successful surgical procedures in worldwide use, thanks to improvements in techniques for cataract removal and developments in  intraocular lens  (IOL) replacement technology, in implantation techniques, and in IOL design, construction, and selection. [ 1 ]  Surgical techniques that have contributed to this success include  microsurgery ,  viscoelastics , and  phacoemulsification . [ 2 ]


Cataract surgery is the removal of the natural  lens  of the  eye  that has developed a  cataract , an opaque or cloudy area. [ 3 ]
Over time, metabolic changes of the crystalline lens fibres lead to the development of a cataract, causing impairment or loss of vision. Some infants are born with  congenital cataracts , and environmental factors may lead to cataract formation. Early symptoms may include strong  glare  from lights and small light sources at night and reduced  visual acuity  at low light levels. [ 4 ] [ 5 ]


Couching  (lens depression) was the original form of cataract surgery, and was used from antiquity.  Chrysippus of Soli , a  stoic   Greek   philosopher  provided the earliest account of it. [ 6 ]  Couching is still occasionally found in traditional medicine in parts of Africa and Asia. In 1753,  Samuel Sharp  performed the first-recorded surgical removal of the entire lens and lens capsule, equivalent to what became known as intracapsular cataract extraction. The lens was removed from the eye through a limbal incision. [ 1 ]  At the beginning of the 20th century, the standard surgical procedure was intracapsular cataract extraction (ICCE). [ 7 ]  In 1949,  Harold Ridley  introduced the concept of implantation of the  intraocular lens  (IOL), which made visual rehabilitation after cataract surgery a more efficient, effective, and comfortable process. [ 1 ]


In 1967, Charles Kelman introduced  phacoemulsification , which uses ultrasonic energy to emulsify the nucleus of the crystalline lens and remove cataracts by aspiration without a large incision. This method of surgery reduced the need for an extended hospital stay and made out-patient surgery the standard. [ 8 ]  In 1985, Thomas Mazzocco developed and implanted the first foldable IOL. Graham Barrett and associates pioneered the use of silicone, acrylic, and hydrogel foldable lenses, making it possible to reduce the incision width. [ 7 ]  In 1987, Blumenthal and Moisseiev described the use of a reduced incision size for ECCE. [ 9 ]  In 1989,  M. McFarland  introduced a self-sealing incision architecture, [ 9 ]  and in 2009,  Praputsorn Kosakarn  described a method for manual fragmentation of the lens, which consists in splitting the lens into three pieces for extraction, allowing a smaller, sutureless incision, and requires implantation of a foldable IOL. This technique uses less expensive instruments and is suitable for use in developing countries. [ 9 ]


Couching is the earliest-documented form of cataract surgery, and one of the oldest surgical procedures ever performed. In this technique, the lens is dislodged and pushed aside into the vitreous cavity, but not removed from the eye, thus removing the opacity from the visual axis, but also the ability to focus. [ 10 ]  After being used regularly for centuries, couching has been mostly abandoned in favour of more effective techniques, due to its generally poor outcomes, and is currently only routinely practised in remote areas of developing countries. [ 11 ] [ 12 ]


Cataract surgery was first mentioned in the  Babylonian   code of Hammurabi  1750  BCE . [ 13 ]  The earliest known depiction of cataract surgery is on a statue from the  Fifth Dynasty of Egypt  (2467–2457  BCE ). [ 13 ]  According to Francisco J Ascaso  et al ,  a "relief painting from tomb number TT 217 in a worker settlement in  Deir el-Medina " shows "the man buried in the tomb,  Ipuy ... one of the builders of royal tombs in the renowned Valley of the Kings, circa 1279–1213 BC" as he underwent cataract surgery. Although direct evidence for cataract surgery in ancient Egypt is lacking, the indirect evidence, including surgical instruments that could have been used for the procedure, show that it was possible. It is assumed that the couching technique was used. [ 13 ] [ 14 ]


Couching was practiced in ancient India and subsequently introduced to other countries by Indian physician  Sushruta  ( c.  6th century BCE), [ 15 ]  who described it in his medical text,  Sushruta Samhita  ("Compendium of Sushruta"); the work's Uttaratantra section [ a ]  describes an operation in which a curved needle was used to push the opaque "phlegmatic matter" [ b ]  in the eye out of the way of vision. The phlegm was then said to be blown out of the nose. The eye would later be soaked with warm, clarified butter before being bandaged. [ 16 ]  The removal of cataracts by surgery was introduced into China from India, and flourished in the  Sui  (581–618  CE ) and  Tang  (618–907  CE ) dynasties. [ 17 ]


The first references to cataract and its treatment in Europe are found in 29 CE in  De Medicina , a medical treatise by Latin encyclopedist  Aulus Cornelius Celsus , which describes a couching operation. [ 18 ]  In 2nd century  CE ,  Galen  of  Pergamon , a prominent Greek physician, surgeon, and philosopher, reportedly performed an operation to remove a cataract-affected lens using a needle-shaped instrument. [ 19 ] [ 20 ]  Although many 20th-century historians have claimed that Galen believed the lens to be in the exact centre of the eye, there is evidence that he understood the crystalline lens is located in the anterior aspect of the eye. [ 21 ]


The removal of cataracts by couching was a common surgical procedure in  Djenné [ 22 ]  and many other parts of Africa. [ 23 ]  Couching continued to be used throughout the  Middle Ages , and is still used to this day in some parts of Africa and in  Yemen . [ 24 ] [ 12 ]  However, it has been proven to be an ineffective and dangerous method of cataract therapy, which often leads to blindness or only partially restored vision. [ 24 ]  The technique has mostly been replaced by extracapsular cataract surgery, including phacoemulsification. [ 25 ]


The lens can also be removed by suction through a hollow instrument: bronze oral-suction instruments that seem to have been used for this method of cataract extraction during the 2nd century  CE  have been unearthed. [ 26 ]  Such a procedure was described by the 10th-century Persian physician  Muhammad ibn Zakariya al-Razi , who attributed it to  Antyllus , a 2nd-century Greek physician. According to al-Razi, the procedure "required a large incision in the eye, a hollow needle, and an assistant with an extraordinary lung capacity". [ 27 ]  This suction procedure was also described by Iraqi ophthalmologist  Ammar Al-Mawsili  in his 10th-century medical text,  Choice of Eye Diseases . [ 27 ]  He presented case histories of its usage, while claiming to have successfully performed it on a number of patients. [ 27 ] : p318   Extracting the lens has the benefit of removing the possibility of the lens migrating back into the field of vision. [ 28 ]  According to oculist  Al-Shādhili , a later variant of the cataract needle in 14th-century Egypt used a screw to grip the lens. It is not clear how often, if ever, this method was used; other writers, including  Abu al-Qasim al-Zahrawi  and Al-Shadhili, appear to have been unfamiliar with this procedure, or claimed it was ineffective. [ 27 ] : p319


On Sep. 18, 1750,  Jacques Daviel  performed the first documented planned primary cataract extraction on a cleric in Cologne. [ 29 ]   In 1753,  Samuel Sharp  performed the first-recorded surgical removal of the entire lens and lens capsule: the lens was removed from the eye through a limbal incision. [ 1 ]  In America, cataract couching may have been performed in 1611, [ 30 ]  while cataract extraction was most likely performed by 1776. [ 31 ]  Cataract extraction by aspiration of lens material through a tube using suction was performed by Philadelphia-based surgeon  Philip Syng Physick  in 1815. [ 32 ]


King Serfoji II , Bhonsle of  Thanjavur , India, reportedly performed cataract surgeries in the early 1800s, according to manuscripts stored in the  Saraswathi Mahal Library . [ 33 ]


In 1884,  Karl Koller  became the first surgeon to apply a  cocaine  solution to the cornea as a local anaesthetic; the news of his discovery spread rapidly, but was not without controversy. [ 34 ] [ 35 ]


At the beginning of the 20th century, the standard surgical procedure was intracapsular cataract extraction (ICCE). The work of  Henry Smith , who first developed a safe, fast way to remove the lens within its capsule by external manipulation, was considered particularly influential; the  capsule forceps , the discovery of enzymatic zonulysis by  Joaquin Barraquer  in 1957, and the introduction of  cryoextraction  of the lens by  Tadeusz Krwawicz  and  Charles Kelman  in 1961 continued the development of ICCE. [ 7 ]  Intracapsular cryoextraction was the favoured form of cataract extraction from the late 1960s to the early 1980s: it consisted in using a  liquid-nitrogen-cooled  probe tip to freeze the encapsulated lens to the probe. This required a large incision and the cornea to be folded back and the anterior chamber to be drained. [ 10 ] [ 36 ] [ 37 ]


In 1949,  Harold Ridley  introduced the concept of implantation of the  intraocular lens  (IOL) which made visual rehabilitation after cataract surgery a more efficient, effective, and comfortable process. [ 1 ]


Artificial IOLs, which are used to replace the eye's natural lens removed during cataract surgery, increased in popularity since the 1960s, and were first approved by the US  Food and Drug Administration  in 1981. The development of IOLs was considered a notable innovation, as patients previously had to wear very thick glasses, or a special type of  contact lens , in order to cope with the removal of their natural lens. IOLs can be used to correct other vision problems, such as toric lenses for correcting astigmatism. [ 38 ]  IOLs can be classified as monofocal, toric, and multifocal lenses. [ 39 ]


Ocular anaesthesia has improved since  Alfred Einhorn  synthesised  procaine  in 1905, which was used in retrobulbar anaesthesia.


Peribulbar anaesthesia was introduced in 1980 by Mandal and David. Since the turn of the millennium, sub-Tenon's anaesthesia hascome into common use, and by ising a blunt cannula to deliver local anaesthetic, the risk of accidentally puncturing the globe is reduced. The more recent tendency is to administer topical local anesthesia without use of a needle. [ 10 ]


Also in the 1960s, the development of  A-scan ultrasound biometry  contributed to provide more accurate predictions of implant refractive strength. [ 40 ]


In 1967, Charles Kelman introduced  phacoemulsification , which uses ultrasonic energy to emulsify the nucleus of the crystalline lens and remove cataracts by aspiration without a large incision. This method of surgery reduced the need for an extended hospital stay and made out-patient surgery the standard. Patients who undergo cataract surgery rarely complain of pain or discomfort during the procedure, although those who have topical anaesthesia, rather than peribulbar block anaesthesia, may experience some discomfort. [ 8 ]


Ophthalmic viscosurgical devices  (OVDs), which were introduced in 1972, facilitate the procedure and improve overall safety. An OVD is a viscoelastic solution, a gel-like substance used to maintain the shape of the eye at reduced pressure, as well as protect the inside structure and tissues of the eye without interfering with the operation. [ 1 ]


In 1980,  D.M. Colvard  made the cataract incision in the sclera, which limited induced astigmatism. [ 9 ]  In the early 1980s,  Danièle Aron-Rosa  and colleagues introduced the  neodymium-doped yttrium aluminum garnet laser  (Nd:YAG laser) for posterior capsulotomy. [ 7 ]  In 1985, Thomas Mazzocco developed and implanted the first foldable IOL. Graham Barrett and associates pioneered the use of silicone, acrylic, and hydrogel lenses. [ 7 ]


According to Cionni  et al  (2006), Kimiya Shimizu began removing cataracts using topical anaesthesia in the late 1980s, [ 7 ]  though Davis (2016) attributes the introduction of topical anaesthetics to  R.A. Fischman  in 1993. [ 1 ]  In 1987, Blumenthal and Moissiev described the use of a reduced incision size for ECCE. They used a 6.5 to 7 mm (0.26 to 0.28 in) straight scleral tunnel incision 2 mm (0.079 in) behind the limbus with two side ports. [ 9 ]


In 1989,  M. McFarland  introduced a self-sealing incision architecture; in 1990,  S.L.Pallin  described a chevron-shaped incision that minimized the risk of induced astigmatism; in 1991,  J.A. Singer  described the frown incision, in which the ends curve away from the limbus, similarly reducing astigmatism. [ 9 ]  Toric IOLs were introduced in 1992 and are used worldwide to correct corneal astigmatism during cataract surgery; [ 38 ] [ 1 ]  they have been approved by the FDA since 1998. [ 41 ]  Also in the late 1990s,  optical biometry  based on partial coherence  infrared   interferometry  was introduced: this technique improves visual resolution, offers much greater precision, and is much quicker and more comfortable than ultrasound. [ 40 ]


According to surveys of members of the  American Society of Cataract and Refractive Surgery , approximately 2.85 million cataract procedures were performed in the United States throughout 2004, while 2.79 million operations were executed in 2005. [ 42 ]  In 2009,  Praputsorn Kosakarn  described a method for manual fragmentation of the lens, called "double-nylon loop", which consists in splitting the lens into three pieces for extraction, allowing a smaller, sutureless incision of 4.0 to 5.0 mm (0.16 to 0.20 in), and requires implantation of a foldable IOL. This technique uses less expensive instruments and is suitable for use in developing countries. [ 9 ]


As of 2013, medical staffs had access to instruments that use infrared  swept-source optical coherence tomography  (SS-OCT), a non-invasive, high-speed method that can penetrate dense cataracts and collects thousands of scans per second, with the ultimate goal of generating high-resolution data in  2D  or  3D . [ 40 ]  As of 2021, approximately four million cataract procedures take place annually in the U.S. and nearly 28 million worldwide, a large proportion of which are performed in India; that is about 75,000 procedures per day globally. [ 43 ]


Hydrodelineation  is a method of separating an outer shell (or multiple shells) of the  lens  of the eye from the central compact mass of inner  nuclear cataract  (also called endonucleus) during a cataract surgery by the forceful irrigation of a fluid into the mass of the nucleus. [ 1 ]  While  hydrodissection  disconnects the lens from the lens capsule, hydrodelineation splits it into endonuclear and epinuclear sections thus reducing the size of the hard nucleus, making its extraction possible through a smaller incision. [ 2 ]  This also facilitates  phacoemulsification .


An injection of fluid into the body of the lens through the cortex against the nucleus of a cataract separates the hardened nuclear cataract from the softer lens cortex shell by flowing along the interface between them. The smaller hard nucleus can then be expeditiously phacoemulsified, while the posterior cortecx serves as a buffer protecting the posterior capsule membrane. The smaller size of the separated nucleus requires less deep and less peripheral grooving and produces smaller fragments after cracking or chopping. The posterior cortex also maintains the shape of the capsule which reduces risk of posterior capsule rupture. [ 3 ]


Hydrodissection  is the use of a directed jet of water to surgically separate tissues. It is generally used to develop tissue planes or divide soft tissues with less trauma than dissection using a cutting instrument. By using an appropriate pressure it will tend to follow the path of least resistance that is close to the direction of the jet. [ 1 ]


In cataract surgery it is used to release the lens from its capsule by projecting a continuous flow of water from a cannula under the flap of the anterior capsule, which lifts the capsule membrane from the lens. By directing the flow the surgeon lifts the membrane around the sides and back of the capsule until the lens is completely loose as a prelude to  phacoemulsification  or direct extracapslar removal.  [ 2 ] [ 3 ]  Hydrodissection is also used in general surgery to release a trapped nerve or to reduce intraoperative blood losses. [ 4 ]


Ignipuncture  ( Latin :  Ignis  (fire) +  puncture ) is the procedure of closing a retinal separation by transfixation of the break via  cauterization . The procedure was pioneered and named by  Jules Gonin  in the early 1900s. [ 1 ]  Due to the risk of severe complications and the advent of lasers for the controlled delivery of energy, ignipuncture became an obsolete procedure; since the 1980s, ignipuncture has been performed using safer techniques like  endophotocoagulation . [ citation needed ]


This article about the  eye  is a  stub . You can help Wikipedia by  expanding it .


Intraocular lens scaffold , [ 1 ]  or  IOL scaffold  technique, is a surgical procedure in  ophthalmology . In cases where the posterior lens capsule is ruptured and the  cataract  is present, an  intraocular lens  (IOL) can be inserted under the cataract. The IOL acts as a scaffold, and prevents the cataract pieces from falling to the back of the eye. The cataract can then be safely removed by emulsifying it with ultrasound and aspiration. This technique is called IOL scaffold, and was initiated by  Amar Agarwal  at  Dr. Agarwal's Eye Hospital  in  Chennai , India.


The technique can be used to support and protect the posterior capsule membrane during a lens swap procedure. [ 1 ]


The lens capsule may be damaged due to trauma, from birth, or by surgery. [ 2 ] [ 3 ]  During cataract surgery, when half or more of the lens remains and the surgeon notices capsule damage; the IOL scaffold technique can be used to capture the lens and prevent further complications. In this technique, the artificial lens or IOL is placed in the sulcus (remaining part of the lens bag) and  phacoemulsification  surgery using  ultrasound  is performed over it. Once the entire lens is removed, the IOL is well positioned on the sulcus. As soon as the surgeon notices the capsular tear or sinking nucleus, anterior chamber infusion can be used to stabilize the chamber. Anterior  vitrectomy  is performed to remove the  vitreous body  in the  pupil  and anterior part of eye. Then the IOL (already planned to be placed in the lens bag) is inserted under the nucleus on the remaining capsule bag. The nucleus is positioned on the IOL and the surgery is completed. [ citation needed ]


By this method, the risk of lens fragments falling into the vitreous body or back part of the eye is reduced. The IOL acts as a barrier or scaffold preventing the lens remnants from falling back. Since separation is present in the posterior (vitreous) eye from the anterior (aqueous) part,  retinal  risks are reduced. Moreover, neither special instruments  nor additional training required once this method is learnt. [ citation needed ]


The intraocular lens scaffold technique was introduced by Dr.  Amar Agarwal  in 2012. He used this technique in a case which had posterior capsular rupture during a  phacoemulsification  procedure. [ 4 ]


The technique can be used for intraoperative nucleus removal during cataract surgery (phacoemulsification), removal of lens dropped on the retina,  Sommering ring  removal, intraocular foreign body removal, and IOL explantation. [ 4 ] [ 5 ] [ 6 ] [ 1 ] [ 7 ] [ 8 ]


In an eye with total loss of bag where no capsular bag remnant is present, glued IOL scaffold is used. [ 5 ]  In this a glued IOL is placed behind the cataract pieces. The glued IOL then works as a scaffold and the cataract pieces are removed with the phaco handpiece using ultrasound. Two partial thickness  scleral  flaps measuring 2.5 to 2.5 mm are made 180 degrees diagonally apart. Infusion is placed by anterior chamber maintainer and sclerotomies are made below the flaps with 20 gauge needle. The IOL is injected below the remaining lens particles and the remaining lens is positioned on the artificial lens or IOL (Fig 2). The  haptics  of the IOL are brought out under the flaps as in the glued IOL method and tucked into the scleral tunnel made with 26 gauge needle at the entry site. The  phacoemulsification  procedure is then continued on the IOL and the  anterior chamber  is formed by the end of the procedure. Scleral flaps and conjunctiva are then closed with fibrin glue.


In the IOL scaffold, the IOL is placed above the  iris  or above some remnant of the capsule. Otherwise, a  glued IOL  then acts as a scaffold. [ citation needed ]


The  Soemmering ring  is the ring-shaped growth of lens cells after surgical removal of cataractous lens in childhood. This is seen as a peripheral ring after pupil dilatation. Patients who undergo artificial lens implantation in an eye that had earlier cataract surgery use this technique to remove the ring remnant. [ 6 ]  Here the IOL is placed with the glued IOL scaffold method, the Sommering ring is dislodged on the IOL, and is removed (Fig 3).


Refractive  surprise can happen after IOL implantation; incorrect lens or power is the probable cause for this. In that situation, the IOL is removed and an IOL of correct power is placed. IOL scaffold is used where the new IOL is placed into the lens bag below the old IOL. The new IOL acts as scaffold or barrier and helps as a platform for the removal of the old lens. [ 1 ]


External foreign bodies can enter the eye and become lodged on the retina or vitreous. This is often removed through the open method of opening through the sclera (white coat of the eye). While removing intraocular foreign bodies (IOFB), it may drop or slip onto the back of the eye (Fig 4). This will prevent the accidental slippage of IOFB into the eye. [ citation needed ]


No increased risk of postoperative complications such as  endothelial  decompensation or post-operative  uveitis  has been reported. [ 7 ] [ 8 ]  Good visual outcomes are obtained. IOL has been reported to be stable without de-centering in both eyes. [ citation needed ]


Intravitreal injection  is the method of administration of drugs into the eye by injection with a fine needle. The medication will be directly applied into the  vitreous humor . [ 1 ]  It is used to treat various eye diseases, such as  age-related macular degeneration (AMD) ,  diabetic retinopathy , and infections inside the eye such as  endophthalmitis . [ 1 ]  As compared to  topical administration , this method is beneficial for a more localized delivery of medications to the targeted site, as the needle can directly pass through the anatomical eye barrier (e.g. cornea, conjunctiva and lens) and dynamic barrier (e.g. tears and aqueous humor). [ 2 ] [ 3 ]  It could also minimize adverse drug effects on other body tissues via the systemic circulation, which could be a possible risk for  intravenous injection  of medications. [ 2 ] [ 4 ]  Although there are risks of infections or other complications, with suitable precautions throughout the injection process, chances for these complications could be lowered. [ 5 ]


Intravitreal injection was first mentioned in a study in 1911, in which the injection of air was used to repair a detached retina. [ 6 ] [ 7 ] [ 8 ]  There were also investigations evaluating intravitreal antibiotics injection using  sulfanilamide  and  penicillin  to treat endophthalmitis in the 1940s, yet due to the inconsistency of results and safety concerns, this form of drug delivery was only for experimental use and not applied in patients. [ 8 ]  It was until 1998, that  fomivirsen (Vitravene™) , the first intravitreal administered medication, was approved by the U.S. Food and Drug Administration (FDA). [ 8 ]


In 2004, when Aiello et al. published the first guidelines for intravitreal injection in the journal 'Retina', fomivirsen was still the only medication licensed by the FDA for intravitreal injection. [ 8 ]  At the end of the year, on December 17, the first intravitreal  anti-VEGF drug   pegaptanib (Macugen)  was also licensed by FDA for treatment of wet age-related macular degeneration (wet AMD). [ 2 ] [ 9 ]


Intravitreal injection has then become more common and a surge in the number of injections performed could be seen. [ 10 ]  Six extra medications, namely  triamcinolone acetonide ,  ranibizumab (Lucentis) ,  aflibercept (Eylea/Zaltrap) ,  dexamethasone ,  ocriplasmin  and  fluocinolone acetonide  were approved for this injection by the end of 2014. [ 2 ]  There are also increasing off-label use of  bevacizumab (Avastin)  for the management of various ophthalmologic diseases, like AMD, retinal vein occlusion and diabetic macular edema. [ 2 ] [ 9 ]  On top of that, the number of intravitreal injections has escalated from less than 3000 per year in 1999, to an estimation of near 6 million in 2016. [ 2 ] [ 7 ]


Intravitreal injection is used to inject a drug into the eye to reduce  inflammation  ( anti-inflammatory ), inhibit the growth and development of new blood vessels ( angiostatic ), or lower the  permeability of blood vessels  (anti-permeability), in turn curing various eye diseases. [ 11 ]


Disorders/diseases that can be treated with intravitreal injection include:


Sometimes, an intravitreal injection of  antibiotics  and  steroids  is given as part of routine  cataract surgery . This avoids having to use drops after surgery. [ 1 ]


Antimicrobials  are intravitreally injected to treat eye infections, such as  endophthalmitis  and  retinitis . [ 10 ]  The medication used depends on the pathogen responsible for the disease.


This type of drug targets on bacterial infection. The first use of intravitreal  antibiotics  was dated back to experiments in the 1940s, in which  penicillin  and  sulfonamides  were used to treat the rabbit endophthalmitis models. [ 10 ] [ 14 ]  Later, more studies proved the beneficial effects of intravitreal antibiotics on acute postoperative endophthalmitis. [ 10 ] [ 14 ]  In the 1970s, Peyman's research on the suggested doses for the medications was published. [ 14 ]  Intravitreal antibiotics then has gradually become the major treatment to manage bacterial endophthalmitis. [ 14 ]  Some common antibiotics administered nowadays are  vancomycin  (for  Gram-positive bacteria ) and  ceftazidime  (for  Gram-negative bacteria ). [ 15 ]


The dosage of antibiotics injected intravitreally is usually low to avoid possible retina toxicity. [ 10 ] [ 14 ]  Some alternative antibiotics have also been tested to replace those that have a higher risk of causing macular toxicity (e.g.  aminoglycosides ). [ 10 ] [ 14 ]  In light of the raised occurrence of  antibiotics resistance , the medications should be chosen and evaluated with the support of  bacterial culture  and  antibiotics sensitivity  test results. [ 14 ]  Sometimes, combinations of different antibiotics may be needed to treat polymicrobial infections (infections that are caused by more than one type of microorganisms), or as an  empirical treatment . [ 14 ]


Antibiotics, such as  moxifloxacin ,  vancomycin , etc., are used perioperatively and postoperatively as a common method of endophthalmitis prevention in cataract surgery. Researches show such injection of antibiotics is more useful to prevent infection as compared to  chemoprophylaxis(chemoprevention)  given topically. [ 16 ]  However, it has recently been controversial whether it has sufficient efficacy for endophthalmitis  prophylaxis , and whether it improves the effectiveness in preventing endophthalmitis by perioperative  povidone-iodine  when used in combination with the antiseptic. [ 16 ]


If the endophthalmitis is suspected to be a fungal infection,  antifungals , such as  amphotericin B  and  voriconazole , could be intravitreally injected to treat the disease. [ 10 ] [ 17 ]  Although amphotericin B has a broad spectrum, voriconazole is more commonly used now as it has a higher efficacy and lower toxicity. [ 10 ]


Since the 1990s, intravitreal  antivirals  have been used to treat  cytomegalovirus retinitis (CMV retinitis)  in immunodeficient patients, such as AIDS patients. [ 10 ] [ 18 ]  Some medications that could be used include  ganciclovir ,  foscarnet , and  cidofovir . [ 10 ] [ 19 ]  The amount and frequency of the intravitreal agent injected varies among the drug chosen: for example, foscarnet has to be given more frequently than ganciclovir as it has a shorter intravitreal half-life. [ 10 ]  If the traditional antiviral therapy fails, a combination of these two medications may be injected. [ 10 ]  On the other hand, antiviral drugs could also be administered for patients with  acute retinal necrosis  due to  varicella-zoster virus  retinitis. [ 10 ]


Vascular endothelial growth factor  (VEGF) is a type of protein the body cells produce to stimulate the growth of new blood vessels. [ 20 ]   Anti-VEGF agents  are chemicals that could inhibit these growth factors to reduce or prevent the abnormal growth of blood vessels, which could lead to damage to the eye and vision. [ 21 ]


Anti-VEGF drugs are often injected to reduce the swelling or bleeding of the retina, which can be used to treat wet age-related macular degeneration (AMD), macular oedema (which could be diabetic), diabetic retinopathy, retinal vein occlusion, etc. [ 22 ]


Some common anti-VEGF drugs are  bevacizumab (Avastin) ,  ranibizumab (Lucentis)  and  aflibercept (Eylea/Zaltrap) . [ 23 ]


The primary use of the  corticosteroids  is to reduce the inflammation by inhibiting the inflammatory  cytokines . [ 11 ]  It could be used to treat numerous eye disorders, such as diabetic retinopathy and retinal vein occlusion. [ 10 ] [ 11 ]


Below are some examples of this type of medication:


Triamcinolone acetonide  is one of the most commonly used steroid agents for the treatment of several retinal conditions. The drug is often seen as an ester in commercial drugs and appears as a white- to cream-colored crystalline powder. [ 11 ]  It is much more soluble in alcohol than in water, which could be the reason for its longer duration of action (around 3 months after 4 mg intravitreal injection of the drug). [ 11 ] [ 24 ]  The drug is also 5 times more potent than  hydrocortisone  while only has a tenth of its sodium-retaining potency. [ 11 ]


It has proven to be effective for the management of abnormal endothelial cell proliferation-associated disorders, and the accumulation of intraretinal and subretinal fluid. [ 11 ]


Dexamethasone  is a potent cytokine inhibitor that is naturally released from human  pericytes . [ 11 ]  It is shown to be able to significantly decrease  intercellular adhesion molecule-1  mRNA and protein levels and therefore reduce  leukostasis  and help maintain the  blood-retinal-barrier . [ 11 ]  Its potency is 5 times greater than triamcinolone acetonide. [ 11 ]  Due to its relatively short half-life, the medication is often given as an  intravitreal implant  for a continuous and stable release to the target site. [ 11 ] [ 25 ]  Some newly developed dexamethasone implants, such as Ozurdex, are made from biodegradable materials that could be intravitreally injected rather than surgically implanted. [ 11 ] [ 26 ]


This corticosteroid is usually used to treat disorders and diseases including macular edema secondary to  retinal vein occlusion ,  pseudophakic cystoid macular edema ,  macular edema  secondary to  uveitis ,  diabetic macular edema , and  age-related macular degeneration . [ 11 ]


Fluocinolone acetonide  is a synthetic corticosteroid as potent as dexamethasone, but with a much lower water solubility, which could be accounted for the extended period of release from the intravitreal implant injected. [ 11 ]  It was also proven to have a localized effect in the  posterior segment of the eye  and is not absorbed into the systemic circulation, thus less likely to give rise to systemic adverse effect. [ 11 ]