The medication could be used in treatment for  noninfectious posterior uveitis  and diabetic macular edema, while applications in the management of other ophthalmic diseases are still under research. [ 11 ] [ 27 ] [ 28 ]


Gene therapy drugs [Lenadogene nolparvovec (Lumevoq)] for Leber's hereditary optic neuropathy (LHON) are delivered intravitreally. These are essentially recombinant viral vectors, containing the gene required for the therapy. [ 29 ]


The injection is usually done at the inferotemporal quadrant (i.e. the lower quadrant away from the nose) of the eye undergoing the procedure, as it is usually more accessible. [ 6 ] [ 12 ]  However, depending on the eye's condition, patient's and the ophthalmologist's preference, other regions could also be used. [ 6 ] [ 22 ]


Patient with  aphakic  (without lens due to cataract surgery), or  pseudophakic  eye (with implanted lens after removal of natural lens) would have the injection 3.0-3.5 mm posterior to the  limbus , while injection to the phakic eye (with natural lens) is done 3.5-4.0 mm posterior to the limbus. [ 6 ]


Like many injections, intravitreal injection is commonly performed in the office setting. [ 30 ] [ 31 ]  An operation room may be a better option to provide a more sterile environment for the procedure to lower the chance of infections, yet it will also increase the costs. [ 30 ]  Since the occurrence of serious post-injection infection (e.g.  endophthalmitis ) is low, in-office intravitreal injection is preferred. [ 30 ] [ 32 ]


The exact procedures and techniques of the intravitreal injection varies among different guidelines, and may depend on the practices of the person performing the injection. Below is an example of the steps for the injection:


The patient usually leans back on the chair (in  supine position ), in which the headrest is stable and the patient is comfortable. [ 12 ] [ 31 ]  Sterile drape is sometimes used to cover the face of the patient and only show the eye for the injection. [ 12 ] [ 33 ]


The specialist first applies  anesthetics  to the eye and eyelid to numb the area, so that the patient will not feel the pain during the procedure. [ 12 ] [ 22 ] [ 31 ]  The type of anesthetic used depends on the practitioner practices and the patient's history. Some common forms of anesthetic used are eye drops (e.g.  tetracaine / proparacaine ) or gel (e.g.  lidocaine  2% or 4% jelly), which is applied  topically . [ 12 ] [ 31 ]  Other choices of anesthesia include the use of lidocaine soaked pledget (a small cotton or wool pad) and  subconjunctival injection  (injection under the  conjunctiva ) of anesthetic agents. [ 23 ]  However, the latter may cause a raised chance of  subconjunctival hemorrhage . [ 12 ]  Sometimes, for an eye with inflammation, a  retrobulbar block  may be given, but usually the topical or subconjunctival anesthesia is sufficient. [ 12 ]  The anesthetic takes time to show the numbing effect, ranging from 1–5 minutes, depending on the chemical chosen. [ 12 ]


The specialist then  sterilizes  the eye and the surrounding area, often with  povidone-iodine  (PVP-I) solution, to prevent any infection in the injected site. [ 22 ] [ 31 ]  Aqueous  chlorhexidine  is used instead in case of adverse effects to povidone-iodine. [ 23 ]


Next, an  eyelid speculum  is placed to retract the eyelids and thus hold the eye open. [ 22 ] [ 31 ]  It helps to prevent contamination of the needle and the injection site by the eyelid or eyelashes. [ 34 ]  Povidone-iodine solution is applied to the conjunctiva at the site of injection. [ 22 ]  Another dose of local anesthetic may be given to the conjunctival surface again (for example, by placing a cotton swab soaked with the anesthetic drug solution over the targeted region), which is followed by the reapplication of PVP-I solution. [ 22 ]


The injection site is measured and marked with a measuring  caliper  or other devices. [ 6 ] [ 33 ]  The patient is then told to look away from the injection site to show the quadrant to be injected, and the doctor inserts the needle at the target site in a single motion into the mid-vitreous cavity. [ 12 ]  Once the needle is in the vitreous cavity, the doctor pushes the plunger to release the drug into the cavity. [ 12 ]  After that, the needle is removed, and the injection site is immediately covered with a cotton swab to avoid vitreous reflux (reflux of fluid from the vitreous cavity). [ 6 ] [ 12 ]  The excess PVP-I solution is rinsed away. [ 12 ]


Finally, the doctor checks the patient's vision and  intraocular pressure (IOP)  of the eye. [ 12 ]  The injection of certain medications, such as triamcinolone acetonide (Kenalog or Triesence), may cause a sudden increase in the IOP, [ 35 ] [ 36 ]  and the patient should be monitored until the pressure returns to a normal level. If a large volume of drug is injected,  paracentesis  may be required. [ 12 ]


Side effects of intravitreal injection can be classified into two categories: drug-related side effects and injection-related side effects. [ 11 ]  For example, in an intravitreal steroid injection, complications could be divided into steroid-related adverse effects and injection-related adverse effects, in which the former most commonly include cataract formation and increase in intraocular pressure (IOP). [ 11 ]


Other examples of potential adverse effects are listed as follows:


A surgery may be required to treat certain severe complications. Some of the above complications could also lead to blindness, or even loss of the eye (in the case of a severe infection). [ 12 ]


Precautions should be taken before, during, and after the injection to lower the chances of complications:


An  iridectomy , also known as a  surgical iridectomy  or  corectomy , [ 1 ]  is the  surgical  removal of part of the  iris . [ 2 ] [ 1 ]  These procedures are most frequently performed in the treatment of  closed-angle glaucoma  and iris  melanoma . [ 1 ]


In  acute angle-closure glaucoma  cases, surgical iridectomy has been superseded by  Nd:YAG laser   iridotomy , because the laser procedure is much safer. Opening the globe for a surgical iridectomy in a patient with high  intraocular pressure  greatly increases the risk of  suprachoroidal hemorrhage , with potential for associated  expulsive hemorrhage . Nd:YAG laser iridotomy avoids such a catastrophe by using a laser to create a hole in the iris, which facilitates flow of  aqueous humor  from the posterior to the  anterior chamber  of the eye. [ 3 ]


Surgical iridectomy is commonly indicated and performed in the following cases: [ citation needed ]


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Micro-invasive glaucoma surgery  ( MIGS ) is the latest advance in surgical treatment for  glaucoma , which aims to reduce  intraocular pressure  by either increasing outflow of  aqueous humor  or reducing its production. MIGS comprises a group of surgical procedures which share common features. [ 1 ]  MIGS procedures involve a minimally invasive approach, often with small cuts or micro-incisions through the  cornea  that causes the least amount of trauma to surrounding scleral and conjunctival tissues.  The techniques minimize tissue scarring, allowing for the possibility of traditional glaucoma procedures such as  trabeculectomy  or  glaucoma valve  implantation (also known as glaucoma drainage device) to be performed in the future if needed. [ 2 ]


Traditional glaucoma surgery generally involves an external (ab externo) approach through the  conjunctiva  and  sclera ; however, MIGS procedures reach their surgical target from an internal (ab interno) route, typically through a self-sealing corneal incision. By performing the procedure from an internal approach, MIGS procedures often reduce discomfort and lead to more rapid recovery periods. [ 1 ] [ 2 ]  While MIGS procedures offer fewer side effects, the procedures tend to result in less intraocular pressure (IOP) lowering than with trabeculectomy or glaucoma tube shunt implantation. [ 3 ]


Glaucoma is a group of  eye disorders  in which there is a chronic and progressive damage of the  optic nerve . [ 4 ]  Increased intraocular pressure (IOP) is the main and only modifiable risk factor, attributed to the progression of the disease. During the last 25 years, glaucoma management has been based in the use of pharmaceutical therapies and incisional surgery. [ 5 ]  MIGS procedures can provide the patient sustained IOP reduction while minimizing the risk and complications associated with glaucoma interventions and decrease the dependence of glaucoma medications. [ 1 ]


MIGS procedures offer an excellent safety profile, with minimal incidence of complications, especially when compared with other forms of glaucoma surgery. [ 1 ] [ 2 ] [ 6 ]


MIGS objective, like all glaucoma surgeries, is to achieve lowering of IOP by either increasing  aqueous humour  outflow, the fluid that is produced by the eye and fills the space between the  cornea  and the  lens , or decreasing the production of aqueous humour. MIGS encompasses numerous devices and techniques, including  trabecular  outflow and  Schlemm's canal  targeted interventions, suprachoroidal outflow,  gonioscopy -assisted procedures, and subconjunctival shunts. [ 7 ]


The  iStent  Trabecular Micro-Bypass Stent, or simply iStent, is the smallest implantable medical device, designed to lower intraocular pressure by facilitating trabecular outflow of aqueous fluid. [ 8 ]  The trabecular outflow is one of the major outflow pathways for aqueous humor in the eye and has been the target of both pharmaceutical and surgical therapeutic approaches in glaucoma. [ citation needed ]


The 1-millimeter long iStent is a  titanium  device inserted via an internal approach through the trabecular meshwork into Schlemm’s Canal, bypassing the trabecular meshwork and facilitating flow of aqueous from the eye. [ 1 ] [ 2 ] [ 3 ]  Studies have shown that the iStent is an effective procedure, typically lowering intraocular pressure to the mid-teens. [ 9 ] [ 10 ]


The iStent is the first MIGS device to get  FDA  approval for implantation in combination with cataract surgery. [ 11 ]  The device has also been shown to offer better IOP control than cataract surgery alone up to one year of follow-up in a large randomized controlled FDA study, although the effectiveness was significantly reduced by 2 years. [ 12 ] [ 13 ]  Safety of the iStent was comparable to cataract surgery alone which is much better than conventional trabeculectomy. [ 12 ] [ 13 ] [ 14 ] [ 15 ]   Common complications include failure to implant the device, touching the iris with the device, and touching the undersurface of the cornea (endothelium) with the device. [ 13 ]  Multiple studies have since confirmed the MIGS-type efficacy and safety profile of the iStent. [ 13 ] [ 16 ]


To address the reduced effectiveness at 2 years, some studies have been performed with multiple iStents. [ 17 ]


A 2019 Cochrane Review found that individuals who receive iStents in combination with cataract surgery may be less likely than those who only receive cataract surgery to need glaucoma eye drops at medium-term follow-up; however, the evidence for this finding was of low quality. [ 18 ]


The trabecular micro-bypass stents have been approved for use in the UK by the  National Institute for Health and Care Excellence (NICE) . [ 19 ]


The CyPass Micro-Stent is the first MIGS device developed for lowering of IOP through the suprachoroidal space (virtual space between the  choroid  and  sclera  created by implantation of the device), a part of the uveoscleral outflow pathway for aqueous humor. The uveoscleral pathway is an important pathway for aqueous outflow and drainage which can account for up to 57% of total outflow. [ 20 ]  Cyclodialysis cleft procedures were initially used to access this pathway with significant IOP lowering, but the cleft was prone to high anatomic variability as well as early postoperative closure due to the lack of a permanent drainage implant with a standardized and uniform conduit. [ 21 ]


It has a microlumen of 300 micrometres (0.012 in) and is designed to augment outflow to the suprachoroidal space in order to control intraocular pressure; it is indicated for the treatment of primary open-angle glaucoma. [ 22 ]  The stent is implanted through an ab interno approach and inserted into the supraciliary space (between the  ciliary body  and sclera), effectively creating a controlled cyclodialysis cleft, which is kept open by the device. [ 23 ] [ 24 ]


The first clinical data on the device was presented in 2010 showed sustained IOP lowering and MIGS-like safety profile. [ 25 ]  This has been substantiated in subsequent studies in the combined setting with  cataract surgery  and as a stand-alone treatment for patients failing glaucoma topical therapy. [ 6 ] [ 23 ] [ 24 ] [ 26 ]  Data from a large randomized controlled study has reported positive efficacy after 2 years of follow-up and will be submitted to FDA for approval. [ 27 ] [ 28 ]  The CyPass device has been CE-marked since 2009.


The CyPass micro-stent was voluntarily withdrawn from the market by manufacturers Alcon in August 2018. [ 29 ]


The Hydrus Microstent is an implantable MIGS device for the treatment of primary open angle glaucoma; implantation of this device can be performed in conjunction with cataract surgery. [ 30 ]  The Hydrus Microstent is the longest of the MIGS devices (8-millimeter long implant), and similar to the iStent it is designed to increase trabecular outflow. [ citation needed ]


The implant is inserted through the trabecular meshwork, thus bypassing resistance of aqueous flow through the tissue.  However, other glaucoma surgeries, such as canaloplasty, have shown that mechanical dilation of  Schlemm's canal  is also associated with a reduction in intraocular pressure. [ 31 ]  The Hydrus Microstent takes advantage of this property by mechanically dilating and holding open Schlemm’s Canal.  The length of the Hydrus Microstent is thought to open approximately one quarter of Schlemm’s Canal, routing aqueous into open downstream collector channels. [ citation needed ]


Clinical data from a randomized controlled study demonstrates efficacy of the device at 1 and 2 years. [ 32 ]  The Hydrus Microstent is currently being investigated in an FDA approved study for mild-to-moderate glaucoma.


The XEN Gel Stent is an implantable transscleral microsurgical device that allows the aqueous fluid to drain from the anterior chamber into the subconjunctival space, a pathway utilized by traditional trabeculectomy and glaucoma drainage device surgeries. [ 33 ]  Unlike the latter two procedures, the XEN Gel Stent is performed through an internal approach and avoids directly incising and disrupting the conjunctiva itself. [ 34 ] [ 35 ]


The 6-millimeter stent is placed through the  trabecular meshwork , with one end of the stent sitting directly underneath the conjunctiva, past the outer wall of the sclera.  The inner tip of the stent sits in the anterior chamber, allowing a direct connection for aqueous to flow into the subconjunctival space. The stent is made of a non-bioreactive material, which does not promote scarring of the conjunctiva. [ 34 ]  The XEN Gel Stent was FDA approved on Nov 22, 2016.


The InnFocus Microshunt is a small tube, 8 mm in length, that is inserted in to the eye to help lower intraocular pressure and reduce the need for medications. A Cochrane Review published in December 2019 did not find any published clinical trials to assess whether the InnFocus Microshunt is safer and more comfortable for patients than standard glaucoma surgery (trabeculectomy). [ 36 ]


The InnFocus Microshunt has now been renamed the Preserflo. [ 37 ]


Aqueous humor is produced in the portion of the eye known as the ciliary body.  The ciliary body contains 72 protrusions known as ciliary processes, from which the aqueous is produced. The destruction of these ciliary processes with a  diode laser , known as cyclophotocoagulation, can be used to decrease the amount of aqueous humor produced, thereby reducing the intraocular pressure. [ citation needed ]


Cyclophotocoagulation traditionally has been performed using an external laser through the sclera, known as transscleral cyclophotocoagulation.  However, side effects of the transscleral approach can include significant inflammation, chronically low intraocular pressure, intraocular bleeding, and permanent shutdown of the eye, known as phthisis. [ 38 ] [ 39 ]  Recent advances have now allowed a diode laser to be combined with a camera (endoscope) allowing for direct visualization of the ciliary processes during the ablation (Endo Optiks, Beaver Visitec, Waltham, MA). [ 40 ]


Endocyclophotocoagulation is indicated for the treatment of both open and closed angle glaucoma and is performed in eyes which have already undergone cataract surgery or performed concomitantly with cataract removal.   The largest investigation of endocyclophotocoaguation has shown a significant decrease in intraocular pressure of up to 10 mmHg, as well as a significant reduction in number of glaucoma medications needed. Reported adverse reactions include intraocular inflammation, bleeding, and cystoid macular edema (swelling of the retina). [ 41 ]  A Cochrane Review published in 2019 found no relevant published studies on endoscopic cyclophotocoagulation to assess its effectiveness compared to other surgical treatments (including other MIGS), laser treatment or medical treatment. [ 42 ]


The  Trabectome , or trabeculectomy ab interno, is a microsurgical device cleared by the U.S. Food and Drug Administration since 2006, used in patients with open angle glaucoma to excise a strip of trabecular meshwork, the tissue primarily responsible for the increased resistance of aqueous outflow in glaucoma. [ 43 ]   The Trabectome uses electrocautery via an internal approach to vaporize the trabecular meshwork, creating a large pathway for aqueous to flow, with minimal trauma to surrounding tissues. The procedure can be performed alone or in conjunction with cataract surgery. [ 44 ]


Trabectome is unique among the MIGS procedures, as there is no physical device implanted inside the eye; the pressure lowering is a direct result from the destruction and removal of the trabecular meshwork.  Studies have found a decrease in intraocular pressure to the mid-teens following the procedure, which has a favorable safety profile. [ 44 ] [ 45 ]  The most common complication from Trabectome surgery is bleeding, which can blur vision and take extra time to recover.  The surgery site can scar over time and the pressure can go back up. [ 15 ]


In early 2014, the NeoMedix received a warning letter from the FDA regarding marketing practices. [ 46 ]


Excimer laser trabeculostomy is a procedure which creates holes in the  trabecular meshwork  to reduce  intraocular pressure  by using a  excimer laser . First developed in 1987, a 2020 review of 8 studies found the procedure reduced intraocular pressure by 20-40% and had generally positive outcomes. [ 47 ]


Minimally invasive strabismus surgery (MISS)  is a technique in  strabismus surgery  that uses smaller incisions than the classical surgical approach to correct the condition, thus minimizing tissue disruption. The technique was introduced by Swiss ophthalmologist  Daniel Mojon  around 2007, [ 1 ]  after the Belgian ophthalmologist Marc Gobin described the idea in 1994 in a French-language textbook. [ 2 ]


MISS is a technique that can be employed for all major types of strabismus surgery like rectus muscle recessions, resections, plications, reoperations, transpositions, oblique muscle recessions, or plications, and adjustable sutures, even in the presence of restricted motility. The smaller openings and the less traumatic procedure are in general associated with faster postoperative rehabilitation and less swelling and discomfort for the patient immediately after the procedure. It is supposed that the technique can be performed as an outpatient intervention in many patients (mainly adults) who would otherwise be hospitalized.  [ 3 ]  A study published in 2017 documented fewer  conjunctival  and eyelid swelling complications in the immediate postoperative period after MISS than after conventional strabismus surgery with long-term results being similar between both groups. [ 4 ]  Another advantage is that MISS technique may decrease the risk of anterior segment  ischemia  in some patients, particularly those suffering from  Graves' ophthalmopathy .  [ 5 ]


In MISS the operating microscope rather than magnifying glasses should be used by the surgeon. Instead of one large opening of the  conjunctiva  as is done in conventional strabismus surgery, several small cuts are placed where the main surgical steps, usually suturing, have to be performed. Openings are placed as far away from the  corneal limbus  as possible to minimize postoperative discomfort. Between two of these incisions, called keyhole openings, there is a "tunnel" used by the surgeon to insert the instrument for the treatment of the eye muscles. [ 6 ]  At the end of the operation, the keyhole openings are closed with resorbable sutures. These mini-incisions are postoperatively covered by the  eyelid . MISS openings markedly reduce the frequency and severity of corneal complications like, for example,  dry eye syndrome  and dellen formation, and will allow wearing  contact lenses  earlier. Long-term benefits are avoidance of an increase in redness of the visible conjunctiva and a decreased scarring of the perimuscular tissue, which will facilitate reoperations - if those should become necessary. [ 7 ]


The results after MISS regarding postoperative ocular alignment are widely described in the so far still limited literature on the technique to be about the same as in classical strabismus surgery. This was documented, for instance, in comparing 40 children; the group that had undergone the minimally invasive procedure, however, did show less swelling of the conjunctiva and the eyelids after surgery. [ 8 ]  Lesser rates of complications and faster reconvalescence have been widely established as the main advantages of MISS. [ 9 ]  The technique's efficacy has been shown for surgery of the rectus muscles [ 10 ] [ 11 ] [ 12 ]  as well as for the surgery of the oblique muscles. [ 13 ]  A group from India reported on the successful performance of MISS in patients with Graves' orbitopathy. [ 14 ]


MISS is more time-consuming than conventional surgery. Operating on the muscles through the tunnel is more demanding on the surgeon. The keyhole cuts may tear in older patients. If the tear involves  Tenon's capsule , a visible scar may result. An excessive bleeding that cannot be stopped makes an enlargement of the cuts necessary to cauterize the vessel. Usually, a conversion to a limbal opening as in classical strabismus surgery can be avoided. There are few reports, though, on complications that are unique to MISS.  [ 15 ]


Nowatske v. Osterloh , 198 Wis.2d 419, 543 N.W.2d 265 (Wis. 1996),  on remand , 201 Wis.2d 497, 549 N.W.2d 256 (Wis. App. 1996), is a case relating to the law of  medical malpractice  in Wisconsin.


The plaintiff, [ 1 ]  Kim Nowatske underwent  retinal reattachment  surgery in his right eye in 1989. [ 2 ]   After the surgery, Nowatske could not see out of the eye in question.  During routine post-operative testing, defendant surgeon used his finger (instead of a  tonometer ) to measure the pressure inside Nowatske's eye and, noting a normal "back-off" response to light, did not specifically ask the patient whether he could see in his right eye or not. [ 3 ]
The patient thought the inability to see was a normal consequence of the surgery.  After the patient was discharged, he experienced severe pain; the surgeon, learning that the patient did not receive the pain medication prescribed, called in a prescription to a local pharmacy without inquiring further of the patient regarding the pain.  The next day, Nowatske was examined by the surgeon and learned that the blindness in the right eye was permanent.  In 1991, he and his wife sued the surgeon, and the case went to trial.  A jury determined that the surgeon was not negligent, [ 4 ]  and the plaintiff appealed.


On appeal, the plaintiff argued:


The  Wisconsin Court of Appeals   certified  the first three legal questions to the  Wisconsin Supreme Court .  The state supreme court agreed to consider only the question of whether the pattern jury instructions were correct or not, and held that the jury instructions contained no  legal error  but "should be improved." [ 5 ]


The Wisconsin Court of Appeals then determined that the questions asked during impeachment were improper, but that this was  harmless error .  Allowing the defendant to demonstrate the use of an ophthalmoscope in the courtroom was within the trial court's discretion, and although the appeals court did "not approve of the involvement of jurors in such a demonstration," [ 6 ]  this had no effect on the outcome of the case and therefore was not reversible error.


Finally, the court of appeals held that "[w]e will sustain a jury verdict if there is any credible evidence to support it.  See   Nieuwendorp v. American Family Ins. Co. , 191 Wis. 2d 462, 472, 529 N.W.2d 594, 598 (1995). Our consideration of the evidence must be done in the light most favorable to the verdict, and when more than one inference may be drawn from the evidence, we are bound to accept the inference drawn by the jury . . . . It is the jury's responsibility to determine the credibility of the witnesses and the weight to be afforded their testimony." [ 7 ]   There was conflicting testimony from experts [ 8 ]  regarding the standard of care (as to whether, after this type of surgery, a doctor may measure  intraocular pressure  using his finger or whether the doctor should use a  tonometer ) and, as it is the role of the jury and not the court of appeals to weigh expert testimony, the court of appeals affirmed the judgment of the trial court. [ 9 ]


Ophthalmic viscosurgical devices  (OVDs) are a class of clear gel-like material used in eye surgery to maintain the volume and shape of the  anterior chamber  of the eye, and protect the intraocular tissues during the procedure. They were originally called  viscoelastic  substances , or just  viscoelastics . Their consistency allows the surgical instruments to move through them, but when there is low  shear stress  they do not flow, and retain their shape, preventing collapse of the anterior chamber. OVDs are available in several formulations which may be combined or used individually as best suits the procedure, and are introduced into the anterior chamber at the start of the procedure, and removed at the end. Their tendency to remain coherent helps with removal, [ 1 ]  as the cohesive variants tend to be drawn into the aspiration orifice without breaking up.


OVDs are used to protect the corneal endothelium from mechanical trauma and to maintain volume and form of the intraocular space during an open incision. The OVD is introduced into the space by syringe through a cannula. [ 2 ]  At the end of the procedure they are removed by aspiration and the space filled with a compatible fluid such as a  buffered saline solution . [ 3 ]


OVDs are commonly used in cataract, cornea, glaucoma, eye trauma, and vitreoretinal surgery. [ 1 ]


Despite the side effects, the advantages of OVDs have made them indispensable in ophthalmic surgery involving the anterior chamber.


There are no known contraindications to the use of a Sodium Hyaluronate Ophthalmic Viscosurgical Device as a surgical aid in ophthalmic anterior segment procedures. [ 4 ]


OVDs can cause excessive post-operative intraocular pressure, particularly if any is left remaining in the eye after surgery. The pressure rise is dose-related. It develops in the first day and will usually resolve spontaneously within three days. This effect is assumed to be a consequence of the large molecules of the OVD causing reduced outflow in the  trabecular meshwork . Various drugs have been used to limit pressure spikes, and while effective, are not entirely predictable in their effects. [ 2 ]


OVD can be trapped behind the IOL in the capsule during normal surgery, and may cause a forward displacement of the IOL, which in turn shifts the focal plane of the IOL towards near vision. [ 2 ]


The properties of an ideal OVD would include: [ 2 ]


The most relevant physical properties for use in ophthalmic surgery are  viscoelasticity ,  viscosity ,  pseudoplasticity , and  surface tension . [ 2 ]


These physical properties of an OVD are consequences of molecular chain length, and molecular interactions between chains. The  rheologic  properties of an OVD directly affect its clinical characteristics. An OVD can be chosen that best matches the requirements for a specific procedure, or part of a procedure, and combinations may be useful. [ 2 ]


Viscoelasticity is the property of  materials  that exhibit both  viscous  and  elastic  characteristics when undergoing  deformation . Viscous materials, like water, resist  shear flow  and  strain  linearly with time when a  stress  is applied. Elastic materials strain when stretched and immediately return to their original state once the stress is removed. Viscoelasticity allows the OVD to retain its shape under low shear stress, and to spring back into shape after a low deforming stress is removed, but also allow instruments to be moved relatively freely when the critical shear stress is exceeded. [ 2 ]


Viscosity is a measure of its the resistance to shear deformation in a fluid at a given rate, or its resistance to flow. It quantifies the internal frictional force between adjacent layers of fluid that are in relative motion. The viscosity of a  Newtonian fluid  does not vary significantly with the rate of deformation.


Pseudoplasticity is the characteristic of a material to rapidly transform from a gel-like consistency to a liquid and back as the shear stress is varied. A high molecular weight, high viscosity OVD at rest retains its shape well. When under
sufficient shear stress it will flow, and alignment of the molecules reduces viscosity to allow rapid flow. Under low shear stress the OVD will quickly revert to an elastic gel, which is a good shock absorber. The highest shear rates occur when the OVD is passed through a cannula, in which state viscosity becomes nearly independent of molecular weight. When the molecules are aligned in the direction of flow, viscosity is determined almost entirely by the concentration. [ 2 ]


Surface tension: The coating ability of an OVD is determined partly by the intermolecular cohesive forces within the OVD, and partly adhesive forces between the OVD and the contacted tissue, instrument or IOL. The contact angle between a drop of the OVD and the other material on a flat surface is an indicator of the ability of the OVD to wet and coat that material. Surface tension is a measure of the cohesion between molecules of the OVD, so a lower surface tension and higher adhesion and contact angle indicate a better ability to wet. A solution of sodium hyaluronate has a significantly higher surface tension and contact angle with the relevant tissues than a solution of chondroitin sulfate, HPMC, or a mixture of sodium hyaluronate and chondroitin sulfate, which indicates better coating by the latter materials. [ 2 ]


Cohesive type OVDs adhere to themselves. They have high viscosity and act like a gel. The molecules have long chains, with high molecular weight, and have high surface tension and pseudoplasticity. They are relatively easy to aspirate as they tend to stay in one piece as they are drawn towards the suction orifice. [ 1 ]


Dispersive tyes have lower surface tension and tend to spread and wet contact surfaces. They have lower viscosity, the molecules are not as strongly mutually attracted, they show low pseudoplasticity and have shorter molecular chains and lower molecular weight. [ 1 ]


The OVD occupies the volume of the anterior chamber during surgery, maintains its volume and shape without requiring internal pressure, and does not flow out through open incisions when undisturbed. It allows the free passage of instruments, prevents low viscosity fluids from leaking out, and provides the surgeon with a clear view of the internal volume. The cohesive nature of some types facilitates rapid removal by aspiration at the end of the procedure. [ 2 ]


OVDs are sterile aqueous saline solutions of one or more viscoelatic compounds and buffers to control pH at 7 to 7.5. [ 2 ]


Meyer and Palmer isolated hyaluronic acid from the vitreous cortex in 1934. [ 5 ]  Also in 1934,  Endre A. Balazs  extracted and purified hyaluronic acid from rooster combs and umbilical cord. [ 1 ]


In 1958, Balazs suggested the possibility of using hyaluronic acid as a substitute for the vitreous substitute during surgery for retinal detachment, and in 1972 made the first injection of hyaluronic acid into the vitreous chamber. [ 1 ]


Ophthalmic viscosurgical devices were introduced in 1972. [ 6 ]  Various alternative formulations with varied physical characteristics have been developed since then. [ 2 ]


Balazs developed the procedure of viscosurgery, coined the term, and patented high molecular weight viscoelastic material using purified hyaluronic acid to be used for implantation of IOLs. [ 1 ]


In 1976 an application for the use of the OVD Healon was made with the FDA, and the next year applications were made for its use in surgery for cataracts, IOL implantation, glaucoma, and corneal transplants. In 1979, 510k permission was granted to market Healon, and FDA approval in January 1983. Since then OVDs have become essential tools in ophthalmic surgery. [ 1 ]


Polyacrylamide  is a synthetic compound that was used for a while but withdrawn from the market in 1991, after its use was found to be associated with elevated intraocular pressure. [ 1 ]


Osteo-odonto-keratoprosthesis  ( OOKP ), also known as  "tooth in eye" surgery , [ 1 ]  is a medical procedure to restore vision in the most severe cases of corneal and ocular surface patients. It includes removal of a tooth from the patient or a donor. [ 2 ]


After removal, a longitudinal  lamina  is cut from the tooth and a hole is drilled perpendicular to the lamina. The hole is then fitted with a cylindrical lens. The lamina is grown in the patients' cheek for a period of months and then is implanted upon the eye.


The procedure was pioneered by the Italian ophthalmic surgeon Professor Benedetto Strampelli in the early 1960s. Strampelli was a founder-member of  the International Intra-Ocular Implant Club  (IIIC) in 1966. [ 3 ]


An operation to graft the OOKP is undertaken in severe  pemphigoid ,  chemical burns ,  Stevens–Johnson syndrome ,  trachoma ,  Lyell syndrome  and multiple  corneal graft  failure. [ 4 ]


There is a significant risk of anatomical failure of lamina in the long term, estimated at 19% in a small study, [ 5 ]  with the main risks being laminar  resorption , particularly in  allografts , and  glaucoma .


Another, bigger study comparing OOKP with the lesser known osteo-keratoprosthesis (OKP) in 145 and 82 patients and follow-up terms up to 10 years yielded the following statistics: [ citation needed ]


Another long-term study of 181 patients puts the chances of retaining an intact OOKP after 18 years at 85%. [ 7 ]


In 2022, a retrospective study conducted on 82 eyes with OOKP using original Strampelli technique, showed an anatomical survival of 94% up to 30 years of follow-up. The same study also reported a visual acuity better than 1.00 logMAR (or 20/200 Snellen) at 10 years in 81% of the eyes, and a visual acuity of 1.21 logMAR (or 20/324 Snellen) at 30 years. [ 8 ]


OOKP is a two-stage operation: [ 9 ]


Stage 1  of the surgery involves five separate procedures:


Stage 2  (about 4 months later) involves two separate procedures:


At the end of the procedure, light can now enter through the plastic cylinder, and the patient is able to see through this cylinder with good vision. [ 3 ]


The procedure was pioneered by the Italian ophthalmic surgeon Professor Benedetto Strampelli [ citation needed ]  in Rome in the early 1960s.


The son of the geneticist and agronomist  Nazareno Strampelli , Benedetto Strampelli held the chair of ophthalmic surgery at Rome's Ospedale di San Giovanni in Laterano where he was one of the first surgeons in Italy to transplant cornea. In 1953 he was the first Italian to implant  intraocular lens  which were manufactured to his own design by  Rayners  in UK. Strampelli was a founder-member with  Harold Ridley  and Peter Choyce of  the International Intra-Ocular Implant Club  (IIIC) in 1966. [ citation needed ]


A  peritomy  is a procedure carried out during  eye surgery , where an incision is made around the  limbus , usually to expose the  sclera  and/or  extraocular muscles  for a variety of surgical procedures. [ 1 ]   [ 2 ]


Photodisruption  is a form of  minimally invasive surgery  used in  ophthalmology , utilizing infrared  Nd:YAG lasers  to form plasma ("lightning bolt"), which then causes acoustic shock waves ("thunderclap") which then in turn affects tissue. [ 1 ] [ 2 ] [ 3 ]  The tissue ruptures as a result of the vapor bubble produced by the laser; the temperature required to produce this effect is between 100 and 305 °C. [ 4 ]


Because the infrared laser is invisible to the surgeon's eye, typically a companion  HeNe laser  is used in conjunction.  However, the eye lens acts as a prism, so the infrared light bends at a shallower angle than the red light, causing  chromatic aberration .  This means the area highlighted by the HeNe laser is not precisely the area being affected Nd:YAG laser, and therefore some surgical lasers have an added adjustment to compensate. [ 2 ]


The first successful use of photodisruption was in 1972, on a case of trabecular meshwork. [ 1 ]   Photodisruption came to wide use in the early 1980s for the treatment of extracapsular cataract extraction. [ 1 ]   The technique is most commonly used for  lithotripsy  of  urinary calculi  and the treatment of posterior  capsulotomy  of the lens. [ 3 ]   When used in corneal surgery, picosecond and nanosecond disruptors are used on the lamellae of the corneal stroma, and the method may be preferable as it leaves the  epithelium  and  Bowman's layer  unharmed.  This modifies the outer corneal curvature, which affects the refractive property of the eye. [ 5 ]


Phototherapeutic keratectomy  (PTK) is a type of  eye surgery  that uses a  laser  to treat various  ocular disorders  by removing  tissue  from the  cornea . PTK allows the removal of superficial  corneal opacities  and surface irregularities. It is similar to  photorefractive keratectomy , which is used for the treatment of  refractive conditions . The common indications for PTK are  corneal dystrophies , scars, opacities, and  bullous keratopathy . [ 1 ]


Pre Descemet's endothelial keratoplasty (PDEK)  is a kind of endothelial  keratoplasty , where the pre descemet's layer (PDL) along with  descemet's membrane  (DM) and  endothelium  is transplanted. [ 1 ]  Conventionally in a  corneal transplantation , doctors use a whole cornea or parts of the five layers of the cornea to perform correction surgeries. In May 2013, Dr  Harminder Dua  discovered a sixth layer between the stroma and the descemet membrane which was named after him as the  Dua's layer . In the PDEK technique, doctors take the innermost two layers of the cornea, along with the  Dua's layer  and graft it in the patient's eye.


The normal cornea (Fig 1) has from the front to the back the following layers:


1. Epithelium


2. Bowman's membrane


3. Stroma


4. Pre Descemets layer


5. Descemet's membrane


6. Endothelium


For the human eye to see, the cornea or the front window of the eye should be clear or transparent. For that to happen the inside corneal layer the endothelium pumps out water from the cornea so that the cornea remains transparent and light can pass into the eye  and one can see. If the endothelium is bad the cornea starts retaining water and gets damaged which is called bullous keratopathy.Thus PDEK helps in replacing the non functioning endothelium in bullous keratopathy.
PDEK is different from the whole cornea transplantation in which the transplantation of entire donor cornea to the recipient is done. [ 2 ] [ 3 ]  Normal corneal thickness is about 520 to 540 microns in the centre and 600 to 620 microns in the periphery. [ 4 ]  Pre descemet's layer which is dissected in PDEK, measures about 10.15±3.6 microns thick. [ 5 ]  The descemet membrane (DM) measures about 16±2 microns (range 13-20μ) thick and the normal endothelium is about 5 microns thick. Hence, the overall thickness of the PDEK graft will be about 32 to 44 microns. [ 6 ]


Prof  Amar Agarwal  ( India ) in 2013, September 4 performed the first  PDEK surgery technique in collaboration with Prof  Harminder Dua  ( UK ) and showed the significance of the Pre Descemets layer in corneal transplantation. [ 7 ]  The initial surgery was performed for pseudophakic bullous keratopathy. Though donor eyes of all age group were used in the initial PDEK cases; there was 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. [ citation needed ]


PDEK surgery can be performed in patients with decompensated cornea like pseudophakic bullous keratopathy, aphakic bullous keratopathy, congenital endothelial decompensation like Fuch's dystrophy of cornea and post traumatic endothelial decompensation. [ 1 ]


PDEK graft can be harvested from donor of any age. [ 8 ]  Easy dissection of PDL layer in infant (less than 1 year), pediatric (1– 15 years) and young donor (15 –40 years) is an added advantage in PDEK procedure, which helps in transfer of viable endothelial cells with maximum regenerating capacity from this group of donors.


PDEK graft is transplanted so far for adult patients who have lost vision due to endothelial decompensation meaning the  Endothelium  is not working. [ 1 ]


Graft can be obtained from a dissected corneoscleral button taken from the deceased. The procedure is performed in sterile operating theatre setup. PDEK graft is prepared initially and kept in the storage medium (Optisol or MK medium) till the recipient bed is prepared. [ 1 ]


The donor corneoscleral rim (donor cornea) is placed on the eye mount with the endothelial side facing the surgeon. A 30 gauge needle attached to a 5 ml syringe filled with sterile air is passed from the limbus (edge of the cornea) into the mid stroma (middle of the corneal layers) with the bevel of the needle facing upwards. Once the needle is stable in the stroma, controlled air injection is performed. Numerous tiny air bubbles are seen cleaving the stroma and finally they coalesce to form one large bubble or Big bubble (BB) (Fig 2A). Once the type 1 BB is formed in the centre, it is gradually enlarged to maximum size which is about 8 mm. Following this, the bubble is pierced with a trephine or knife (Fig 2B) and the graft is dissected meticulously. It is then stained with a dye (trypan blue) and delineated well (Fig 2C, D). The dissected PDEK graft is then placed in a storage medium till the recipient (patient) is ready for transplantation. [ citation needed ]


After obtaining the informed consent from the patient, local anesthesia is given. Anterior chamber entry (eye entry) is made by a blade in the superior corneo-limbus area. Descemet's membrane along with endothelium in the patient is removed mechanically by reverse Sinskey hook by controlled stripping on the endothelial side [ citation needed ]  (Fig 3A-C).


The PDEK graft which is already preserved in the storage medium is then placed in an injector (Fig 3A). The graft takes a shape of scroll immediately after dissection and the surgeons maintains the integrity or orientation of the scroll throughout the procedure. The injector along with the graft is inserted via the corneal wound and the graft is injected in the anterior chamber (Fig 3C). Initially the graft is made sure that it is oriented with endothelium down and PDL against the host stroma. This can be confirmed by using an endoilluminator because in eyes with corneal decompensation, the clarity is usually poor and the visualization of graft is affected under naked eye.8 once the orientation is confirmed, the graft is unfolded under saline (Fig 3D). Then the graft is attached to the overlying host stroma pneumatically (Fig 3E,F). Air fluid pressure is maintained inside the chamber for 60 seconds and then minimal air is released. The wound is closed with 10-0 monofilament suture and subconjunctival antibiotic steroid injection is given. [ citation needed ]


Normal human lens is placed inside a capsular bag by nature. During trauma, surgery or sometimes by genetic cause the bag is damaged, weak or absent. Under this condition, one cannot place a normal intraocular lens (IOL) in the bag. To overcome this problem, the technique of glued IOL was introduced by Prof Amar Agarwal in 2007, December for lens implantation in eyes with the absent or deficient capsular bag.9,10 Here 2 scleral flaps about 180 degrees apart are made and the IOL is inserted through the corneal incision (Fig 3). After making the sclerotomy below the flaps, the haptics are externalized and tucked in a scleral tunnel at the point of exit. Maggi and Maggi in 1997 were the first to report sutureless scleral fixation of a special IOL. Gabor Scharioth and Pavilidis in 2006 reported the scleral tuck and intrascleral haptic fixation of a posterior chamber Intra ocular lens (PC IOL). Fibrin glue is applied for apposing the flaps and conjunctiva. PDEK can be combined or performed simultaneously with glued IOL implantation in eyes with existing corneal decompensation with aphakia, IOL decenteration or dislocated lens. Sometimes, one may require removal of the existing lens (as in Anterior Chamber IOL) and replacement with the other by this method. So far we have seen good anatomical and functional outcome in combined PDEK with glued IOL (Fig 4).


Normal endothelial cell count at birth is about 4000 cells/sq mm. Adult population has a count of about 2500 to 2800 cells/Sq mm and loses around 0.6% cells per year. The cells in infant have potential regenerating capacity unlike the adult cell and this can be utilized for PDEK to obtain excellent functional outcome. Infant donor eyes are eyes of donor less than or equal to 1 year. In our experience we noticed that the infant donors have maximum viable cells which can expand and cover the entire cornea in a decompensated adult cornea. Because type 1 BB is formed easily in young corneas, this is an added advantage in PDEK which can be performed in infant donors. Our preliminary results on Infant donor PDEK have been excellent and we expect to do more research on the functional differences in the young donors.7


Post operatively these patients are given topical steroids and antibiotics for 1 month. Low dose steroids are kept in maintenance for one year. Topical lubricants are prescribed according to the ocular surface changes. Preservative free lubricants are initiated in patients with immediate epithelial changes. Intraocular pressure is monitoring on regular basis to assess the steroid induce glaucoma. Follow up visits are preferred as day 1, day 3, day 7, 2 weeks, 1 month, 3 months and then 6 monthly. Post operative anterior segment optical coherence tomography may be performed for assessing the anatomical success of the technique.


From the patient's point of view, the chances of rejection are less as compared to whole corneal transplantation as the PDEK graft has minimal PDL layer hence.11,12 Early visual rehabilitation is obtained (Fig 5) and the suture related complications are minimized. From the surgeon's point, PDEK graft is thicker than isolated DM graft and hence there is less intraoperative graft handling challenges like torn graft, tissue loss or ragged edges. Pneumatic dissection induced endothelial cell loss is also noted to be not higher than or in fact better than other endothelial keratoplasty.13 Since it is harvested from all age groups, the limitation of donor age is lessened. Minimal interface opacification, less refractive shift and reduced topographic changes are the extra benefits of PDEK.


Intraoperatively, bubble related problems can happen in early learning curve. This can be managed by proper positioning of needle and controlled intrabubble pressure. Postoperative graft detachment can happen in eyes with insufficient air or loss of air after surgery.1,6 If the graft is detached in the centre and there is significant cornea edema, immediate graft repositioning by air is performed in operating theatre under sterile precautions.


In the last one and half year, many patients have been benefitted by PDEK surgery.1,6,7 Early visual recovery and less post operative inflammation is the main advantage. Young donor eyes seemed to have made a huge difference in the visual quality and functional outcome. There are additional research studies in progress to elucidate the regenerating capacity of the endothelial cells in vivo.


A  pterygium  of the eye ( pl. :  pterygia  or  pterygiums , also called  surfer's eye ) is a pinkish, roughly triangular tissue growth of the  conjunctiva  onto the  cornea  of the  eye . [ 2 ]  It typically starts on the cornea near the nose. [ 3 ]  It may slowly grow but rarely grows so large that it covers the  pupil  and impairs vision. [ 2 ]  Often both eyes are involved. [ 5 ]


The cause is unclear. [ 2 ]  It appears to be partly related to long term exposure to  UV light  and dust. [ 2 ] [ 3 ]  Genetic factors also appear to be involved. [ 4 ]  It is a  benign growth . [ 6 ]  Other conditions that can look similar include a  pinguecula , tumor, or  Terrien's marginal corneal degeneration . [ 5 ]


Prevention may include wearing sunglasses and a hat if in an area with strong sunlight. [ 2 ]  Among those with the condition, an  eye lubricant  can help with symptoms. [ 2 ]  Surgical removal is typically only recommended if the ability to see is affected. [ 2 ]  Following surgery a pterygium may recur in around half of cases. [ 2 ] [ 6 ]


The frequency of the condition varies from 1% to 33% in various regions of the world. [ 7 ]  It occurs more commonly among males than females and in people who live closer to the equator. [ 7 ]  The condition becomes more common with age. [ 7 ]  The condition has been described since at least 1000 BC. [ 8 ]


Symptoms of pterygium include persistent redness, [ 9 ]  inflammation, [ 10 ]  foreign body sensation, tearing, dry and itchy eyes. In advanced cases the pterygium can affect vision [ 10 ]  as it invades the cornea with the potential of obscuring the optical center of the cornea and inducing astigmatism and corneal scarring. [ 11 ]  Many patients do complain of the cosmetic appearance of the eye either with some of the symptoms above or as their major complaint. The use of standard contact lenses can become uncomfortable or even impossible although custom shaping may improve the fit to some extent. [ citation needed ]


The exact cause is unknown, but it is associated with excessive exposure to wind, sunlight, or sand. Therefore, it is more likely to occur in populations that inhabit the areas near the equator, as well as windy locations.  In addition, pterygia are twice as likely to occur in men than women.


Pterygium in the conjunctiva is characterized by elastotic degeneration of  collagen  ( actinic elastosis [ 12 ] ) and fibrovascular proliferation.  It has an advancing portion called the head of the pterygium, which is connected to the main body of the pterygium by the neck.  Sometimes a line of iron deposition can be seen adjacent to the head of the pterygium called  Stocker's line .  The location of the line can give an indication of the pattern of growth.


The predominance of pterygia on the nasal side is possibly a result of  peripheral light focusing , where the sun's rays passing laterally through the  cornea , where they undergo refraction and become focused on the  limbic  area.  Sunlight passes unobstructed from the  lateral  side of the eye, focusing on the  medial  limbus after passing through the cornea.  On the  contralateral  (medial) side, however, the shadow of the nose medially reduces the intensity of sunlight focused on the  lateral / temporal   limbus . [ 9 ]


Some research also suggests a genetic predisposition due to an expression of  vimentin , which indicates cellular migration by the keratoblasts embryological development, which are the cells that give rise to the layers of the cornea. Supporting this fact is the congenital pterygium, in which pterygium is seen in infants. [ 13 ]  These cells also exhibit an increased P53 expression likely due to a deficit in the  tumor  suppressor gene. These indications give the impression of a migrating  limbus  because the cellular origin of the pterygium is actually initiated by the limbal epithelium. [ 14 ]


The pterygium is composed of several segments:


Pterygium (conjunctiva) can be diagnosed without need for a specific exam, however  corneal topography  is a practical test (technique) as the condition worsens. [ 15 ] [ 16 ]


Pterygium should be differentiated from  pinguecula , which is histologically and etiologically similar to pterygium. [ 17 ] [ 18 ]  Unlike pterygium, pinguecula is seen only on the conjunctiva, it will not progress to limbus or cornea.


Another condition which is similar to pterygium is inflammatory adhesion of conjunctiva to cornea known as  pseudopterygium . Unlike pterygium, it may occur anywhere around cornea and the adhesion is usually limited to its apex. [ 18 ]


As it is associated with excessive sun [ 19 ]  or wind exposure, wearing protective  sunglasses  with side shields and/or wide brimmed hats and using artificial tears throughout the day may help prevent their formation or stop further growth. Surfers and other water-sport athletes should wear eye protection that blocks 100% of the UV rays from the water, as is often used by snow-sport athletes. Many of those who are at greatest risk of pterygium from work or play sun exposure do not understand the importance of protection. [ 20 ] [ 21 ]


A pterygium typically does not require surgery unless it grows to such an extent that it causes visual problems. [ 2 ]  Some of the symptoms such as irritation can be addressed with artificial tears. [ 2 ]  Surgery may also be considered for unmanageable symptoms. [ 22 ]


A  Cochrane review  found conjunctival autograft surgery was less likely to have reoccurrence of the pterygium at 6 months compared to amniotic membrane transplant. [ 23 ]  More research is needed to determine which type of surgery resulted in better vision or quality of life. [ 23 ]  The additional use of  mitomycin C  is of unclear effect. [ 23 ]   Radiotherapy  has also been used in an attempt to reduce the risk of recurrence. [ 24 ]


Conjunctival auto-grafting is a surgical technique that is an effective and safe procedure for pterygium removal. [ 25 ]  When the pterygium is removed, the tissue that covers the sclera known as the Tenons layer is also removed.  Auto-grafting covers the bare sclera with conjunctival tissue that is surgically removed from an area of healthy conjunctiva. That "self-tissue" is then transplanted to the bare sclera and is attached using sutures or tissue adhesive.


Amniotic membrane transplantation is an effective and safe procedure for pterygium removal. Amniotic membrane transplantation offers practical alternative to conjunctival auto graft transplantation for extensive pterygium removal. Amniotic membrane transplantation is tissue that is acquired from the innermost layer of the human placenta and has been used to replace and heal damaged mucosal surfaces including successful reconstruction of the ocular surface. It has been used as a surgical material since the 1940s, and has been shown to have a strong anti-adhesive effect.


Using an amniotic graft facilitates epithelialization, and has anti-inflammatory as well as surface rejuvenation properties. Amniotic membrane transplantation can also be attached to the sclera using sutures, or glue adhesive. [ 26 ] [ 27 ] [ 28 ]  Amniotic membrane by itself does not provide an acceptable recurrence rate. [ 29 ]


A  scleral buckle  is one of several  ophthalmologic  procedures that can be used to repair a  retinal detachment . Retinal detachments are usually caused by retinal tears, and a scleral buckle can be used to close the retinal break, both for acute and chronic retinal detachments. [ citation needed ]


Scleral buckles come in many shapes and sizes. A silicone sponge (with air filled cells) is a cylindrical element that comes in various sizes. An encircling band is a thin  silicone  band sewn around the circumference of the  sclera  of the  eye . A solid silicone grooved tyre element is also used. Buckles are often placed under a band to create a dimple on the eye wall. [ citation needed ]


The scleral buckle is secured around the eyeball under the  conjunctiva . This moves the wall of the eye closer to the detached retina. This alteration in the relationships of the tissues seems to allow the fluid which has formed under the retina to be pumped out, and the retina to re-attach. The  physics  or  physiology  of this process are not fully understood. [ citation needed ]


Retinal detachment surgery usually also involves the use of  cryotherapy  or  laser photocoagulation . The laser or cryotherapy forms a permanent adhesion around the retinal break and prevents further accumulation of fluid and re-detachment. The usage of scleral buckle is a source of debate only for complex retinal detachment surgery amongst surgeons, and research has been conducted to compare safety and effectiveness outcomes of scleral buckling,  pars plana vitrectomy  with scleral buckle versus  pars plana  victrectomy without scleral buckle. [ 1 ]


Scleral buckles are done using local or general  anesthesia  and are often done as  outpatient  procedures. In the majority of treatments the buckle is left in place permanently, although in some instances the buckles can be removed after the retina heals.  The buckle may also be removed in the event of infection.


A link between scleral buckles and  Adie syndrome  may exist. [ 2 ]


Results from three randomized controlled trials of 274 patients comparing retinal detachment outcomes from  pneumatic retinopexy  versus scleral buckle found some evidence suggesting that scleral buckle was less likely to result in a recurrence of retinal detachment than pneumatic retinopexy but that overall evidence is of low quality and insufficient. [ 3 ]


Sclerotomy  is a  medical intervention  that involves  surgical cutting  in the white area of the eye, known as the  sclera . [ 1 ]  The goal of this intervention is usually done to correct defects in sclera that resulted as a complication of  glaucoma  of other  ocular diseases . [ 2 ]  Sclerotomy can be divided into anterior sclerotomy and posterior sclerotomy. [ 3 ]


The sclerotomy incisions are made by:


Strabismus surgery  (also:  extraocular muscle surgery ,  eye muscle surgery , or  eye alignment surgery ) is  surgery  on the  extraocular muscles  to correct  strabismus , the misalignment of the  eyes . [ 1 ]  Strabismus surgery is a one-day procedure that is usually performed under general anesthesia most commonly by either a neuro- or pediatric ophthalmologist. [ 1 ]  The patient spends only a few hours in the hospital with minimal preoperative preparation. After surgery, the patient should expect soreness and redness but is generally free to return home. [ 1 ]


The earliest successful strabismus surgery intervention is known to have been performed on 26 October 1839 by  Johann Friedrich Dieffenbach  on a 7-year-old esotropic child; a few earlier attempts had been performed in 1818 by William Gibson of Baltimore, a general surgeon and professor at the University of Maryland. [ 2 ]  The idea of treating strabismus by cutting some of the extraocular muscle fibers was published in American newspapers by New York oculist John Scudder in 1837. [ 3 ]


Strabismus surgery is one of many options used to treat any misalignment of the eyes, called strabismus. This misalignment or "crossing" of the eyes can be caused by a variety of issues. Surgery is indicated when other, less invasive methods have been unable to treat the misalignment or when the procedure will significantly improve quality of life and/or visual function. [ 4 ]  The type of surgery for a given patient depends on the type of strabismus they are experiencing. Exodeviations are when the misalignment of the eyes is divergent ("crossing out") and esodeviations are when the misalignment is convergent ("crossing in"). [ 4 ]  These conditions are further categorized based on when the misalignment is present. If it is latent the condition is called a "-phoria" and if it is present all the time it is a "-tropia". [ 4 ]   Esotropias measuring more than 15 prism diopters (PD) and exotropias more than 20 PD that have not responded to refractive correction can be considered candidates for surgery. [ 5 ]


The goal of strabismus surgery is to correct misalignment of the eyes. This is achieved by loosening or tightening the extraocular muscles in order to weaken or strengthen them, respectively. [ 1 ]  There are two main types of extraocular muscles - rectus muscles and oblique muscles - which have specific procedures to achieve the desired results. [ 4 ]  The amount of weakening or strengthening required is determined through in-office measurements of the eye misalignment. Measured in PD, the size of the deviation is used along with established formulas and tables to inform the surgeon how the muscle must be manipulated in surgery. [ 4 ]


The main procedure used to weaken a rectus muscle is called a recession. [ 4 ]  This involves detaching the muscle from its original insertion on the eye and moving it towards the back of the eye a specific amount. [ 1 ]  If after a recession the muscle requires more weakening a marginal myotomy can be performed, where a cut is made part way across the muscle. [ 4 ]  The procedures used to strengthen rectus muscles include resections and plications. A resection is when a portion of the muscle is cut away and the new shortened muscle is reattached to the same insertion point. A plication on the other hand is when the muscle is folded and secured to the outer white portion of the eye, known as the sclera. [ 4 ]  Plication has the advantages of being a quicker procedure that involves less trauma than a resection and preserves the anterior ciliary arteries - the latter of which minimizes the risk of blood loss to the front of the eye allowing for operation on multiple muscles at one time. [ 6 ]  Studies on horizontal rectus muscle surgeries have shown that both procedures have similar success rates and no difference in post-operative exodrift or overcorrection rate was discovered. [ 6 ]  However, further investigation is required to determine if there is any difference in long term effects from the two procedures. [ 6 ]


Because of the antagonistic pairings of the rectus muscles and the fact that strabismus can be a binocular problem, in certain cases surgeons have the option of operating on either one eye or both eyes. For example, a recent study compared the outcomes of bilateral lateral rectus recession and unilateral recession/resection of the later/medial recti for intermittent exotropia. [ 7 ]  This study showed that the unilateral procedure had higher success rates and lower recurrence rates for this specific condition. [ 7 ]  This is not necessarily true for all types of strabismus and further investigation is required to reach a consensus on this particular aspect of the surgery. [ citation needed ]


There are two oblique muscles attached to the eye - the superior oblique and the inferior oblique - which each have their respective procedures. [ 4 ]


The inferior oblique is weakened through a recession and anteriorization where the muscle is detached from the eye and reinserted at a spot anterior to the original insertion. [ 4 ]  Some surgeons will alternatively perform a myotomy or myectomy, where a muscle is either cut or has a portion of it removed, respectively. [ 4 ]  The inferior oblique muscle is rarely tightened due to the technical difficulty of the procedure and the possibility of damage to the macula, which is responsible for central vision. [ 4 ]


The superior oblique is weakened through either a tenotomy or tenectomy, where part of the muscle tendon is either cut across or removed, respectively. [ 4 ]  The superior oblique is strengthened by folding and securing the tendon to reduce its length, which is called a tuck. [ 4 ]


A technique that is more commonly used for more complicated cases of strabismus is that of adjustable suture surgery. This technique allows for the adjustment of sutures after the initial procedure in order to theoretically achieve a better and more individualized result. This often requires dedicated and specific training in this uncommon procedure that has been reported to be performed in only 7.42% of all strabismus cases. [ 8 ]  Studies have not shown any significant advantage to performing this type of surgery on most forms of simple strabismus. However, its use in some complex cases such as reoperations, strabismus with large or unstable angle, or strabismus in high myopia has been indicated. [ 8 ]  The specific circumstances in which this technique is considered to be superior to non-adjustable suture surgery require further investigation. [ citation needed ]


A relatively new method, primarily devised by Swiss ophthalmologist  Daniel Mojon , is  minimally invasive strabismus surgery (MISS) [ 9 ]  which has the potential to reduce the risk of complications and lead to faster visual rehabilitation and wound healing. Done under the operating microscope, the incisions into the conjunctiva are much smaller than in conventional strabismus surgery. A study published in 2017 documented fewer conjunctival and eyelid swelling complications in the immediate postoperative period after MISS with long-term results being similar between both groups. [ 10 ]  MISS can be used to perform all types of strabismus surgery, namely rectus muscle recessions, resections, transpositions, and plications even in the presence of limited motility. [ 11 ]


A strabismus surgery is considered a success when the overall deviation has been corrected 60% or more or if the deviation is under 10 PD 6 weeks after the surgery. [ 5 ]


Surgical intervention can result in the eyes being entirely aligned ( orthophoria ) or nearly so, or it can result in an alignment that is not the desired result. There are many possible types of misalignment that can occur after the surgery including undercorrection, overcorrection, and torsional misalignment. [ 12 ]  Treating a case of unsatisfactory alignment often involves prisms, botulinum toxin injections, or more surgery. The likelihood that the eyes will stay misaligned over the longer term is higher if the patient is able to achieve some degree of  binocular fusion  after surgery than if not. [ 4 ]  There is tentative evidence that children with infantile esotropia achieve better  binocular vision  post-operatively if the surgical treatment is performed early ( see:   Infantile esotropia ). A recent study reported the reoperation rate in a sample of over 6000 patients being 8.5%. [ 13 ]


Strabismus has been shown to have a variety of negative psychosocial effects on affected patients. Patients are often more fearful, anxious, have lower self-esteem, and increased interpersonal-sensitivity. [ 14 ]  These negative impacts often start in childhood and then progress throughout childhood and adolescence if the misalignment is not corrected quickly. [ 14 ]  There is also data to suggest that society sees this condition as one that negatively affects many qualities important to self-sufficient function such as responsibility, leadership ability, communication, and even intelligence. However, much of this critical mental health burden has been shown to be relieved by corrective surgery. [ 14 ]  Significant increases in self confidence and self-esteem as well as a reduction in general as well as social anxiety was observed. Overall, strabismus surgery has been shown to successfully improve upon many of the negative impacts strabismus can have on one's mental health. [ 14 ]


Complications that occur rarely or very rarely following surgery include: eye infection, hemorrhage in case of scleral perforation, muscle slip or detachment, or even loss of vision. Eye infection occurs at a rate between 1 in 1100 and 1 in 1900 and can lead to permanent loss of vision if not properly treated. [ 15 ]  Surgeons take many measures to prevent infection such as careful surgical draping, using povidone iodine as both drops and a solution to soak the sutures in, as well as a post-op course of steroids and antibiotics. [ 15 ]  There is generally minimal bleeding during strabismus surgery, but medications such as anti-platelet agents and anticoagulants can lead to vision threatening complications retrobulbar hemorrhage. [ 16 ]


Diplopia , or double vision, occurs commonly after strabismus surgery. Although the surgery can be used to treat some types of double vision, it can instead end up making existing symptoms worse or create a new type of double vision. [ 12 ]  The type of double vision can be horizontal, vertical, torsional, or a combination. Treatment of the double vision depends on both the type of double vision and the ability of two eyes to work together, also called binocular function. [ 12 ]  Diplopia with normal binocular function is treated with prism glasses, botulinum injections into the muscles, or repeated surgery. [ 12 ]  If binocular function is not normal, a more individualized approach is necessary to best suit the patient's needs. [ 12 ]


Eye muscle surgery gives rise to scarring ( fibrosis ) as a result of the trauma caused to the ocular tissues. [ 4 ]  The goal of surgery is to produce a thin line of firm scar tissue where the muscle is reattached to the sclera. However, the process of surgery can also result in the formation of scar tissue on other parts of eye. These adhesions can, in rare cases, affect the motion of the eye and the desired alignment. [ 17 ]  If scarring is extensive, it may be seen as raised and red tissue on the white of the eye. [ 4 ]  Fibrosis reducing measures such as cryopreserved amniotic membrane and  mitomycin C  have been shown to have some utility during surgery. [ 17 ]


Very rarely, potentially life-threatening complications may occur during strabismus surgery due to the  oculocardiac reflex . [ 18 ]  This is a physiologic reflex that is described as a reduction in heart rate due to pressure on the globe or traction on the extraocular muscles. It involves activation of the trigeminal nerve leading to activation of the vagus nerve due to the internuclear communication. [ 18 ]  Although the most common arrhythmia is sinus bradycardia, asystole can be seen in its severe form. [ 4 ]  The reflex can also have non cardiac effects such as postoperative nausea and vomiting, which is an extremely common consequence of strabismus surgery in children. [ 18 ]


Toric Markers  are markers made for marking on the outside of the  cornea  or  sclera  part of the eye.
They are designed with semi-sharp or pointed line or dot patterns.


There are two kinds of markers - Pre-Op markers and Intra-Op markers. [ 1 ]


Pre-Op markers: these are used before the patient lies down for surgery. The marking is done when the patient is sitting up with eyes looking forward.
The patterns are usually two lines that indicate one of the following


Intra-Op markers: these are used during surgery, with the patient lying down on the surgery table, and doctor operating with a microscope.
In a few cases, the markers are used during the surgery, along with a degree gauge.


The  Trabectome  is a surgical device that can be used for ab interno trabeculotomy, a minimally invasive glaucoma surgery for the surgical management of adult, juvenile, and  infantile glaucoma . The trabecular meshwork is a major site of resistance to aqueous humor outflow. As angle surgeries such as Trabectome follow the physiologic outflow pathway, the risk of complications is significantly lower than filtering surgeries. Hypotony with damage to the macula ( hypotony maculopathy ),  can occur with pressures below 5 mmHg, for instance, after traditional trabeculectomy, because of the episcleral venous pressure limit. The Trabectome handpiece is inserted into the anterior chamber, its tip positioned into  Schlemm's canal , and advanced to the left and to the right. Different from cautery, the tip generates plasma to molecularize the trabecular meshwork and remove it drag-free and with minimal thermal effect. Active irrigation of the trabectome surgery system helps to keep the anterior chamber formed during the procedure and precludes the need for ophthalmic viscoelastic devices. Viscoelastic devices tend to trap debris or gas bubbles and diminish visualization. The Trabectome decreases the intra-ocular pressure typically to a mid-teen range and reduces the patient's requirement to take glaucoma eye drops and glaucoma medications (see references). The theoretically lowest pressure that can be achieved is equal to 8 mmHg in the episcleral veins. This procedure is performed through a small incision and can be done on an outpatient basis. [ 1 ]


When abdomino-interno trabeculectomy is combined with cataract surgery, it is initially performed for optimal angle visualization. Corneal clarity is often damaged during cataract surgery, and this damage may only be noticeable during gonioscopy, when the light path through the cornea is longer. An iris-lanar clear corneal incision of 1.8 mm width is made approximately 2 mm in front of the surgical limbus. Cataract surgery uses a larger keratome that requires the incision to be closed, to reduce fluid leakage. No viscoelastic is used, as it can cause bipolar electrodes to carbonize during the incision. The patient's head is then turned away from the surgeon by approximately 40 degrees, and the microscope is turned to the same extent in the opposite direction.


Optimum gonioscopic trabecular meshwork visualization requires an angle of approximately 70 to 80 degrees between the microscope and the patient's eye. An incision is made, which is slightly gaping. This gaping encourages hypotony and enables easy identification of Schlemm's canal from refluxed blood. Trypan blue can also be used to stain the trabecular meshwork [18].


The trabectome handpiece is inserted, with irrigation turned on. If the anterior chamber is too shallow for it to be fully inserted, the irrigation ports in the metal sleeve can form the anterior chamber by resting against the outer edges of the incision, with the tip already inside the eye. Right-handed surgeons find it easiest to perform counterclockwise removal first. The trabectome is engaged in the trabecular meshwork. This is done with the tip angled 45 degrees upward, just in front of the scleral spur. This angle offers a pointed entry into the meshwork. The trabectome is then moved in a strictly parallel fashion, with no movement toward the wall of the canal. The handpiece is turned 180 degrees, completing the clockwise removal. The superior and inferior angle structures can be seen, and almost 180 degrees of meshwork are removed by tilting the goniolens toward the patient's brow and then toward their cheek. This can be done in reverse, depending on which eye is operated on.


Once complete, the trabectome is carefully removed from the eye. Viscoelastic is injected into the eye for pressurization, and to tamponade the reflux heme. If cataract surgery is to follow, the microscope and patient's head are returned to their initial positions. The existing access point is used, and a larger keratome is employed to create a larger incision, with a self-sealing biplanar wound [2].


Microincisional glaucoma surgery [3, 4] is conducted in a space that is approximately 200 times smaller than the space used to implant epibulbar glaucoma drainage devices [5] As such, this type of surgery is particularly challenging to learn. The deep venous plexus distal to the outer wall of Schlemm's canal, the iris root, the ciliary body band and the suprachoroidal space all risk being damaged during surgery. This damage can cause variable sequelae [6, 7].


To master this surgery, it is important to be able to visualize the angle, identify the correct target, avoid trauma and maximize meshwork removal. Microincisional glaucoma surgery does not yet have dedicated simulators or synthetic models such as those used in cataract surgery wet labs. Therefore, most aspiring surgeons in this field practice on glaucoma patients. This is despite reported complications being almost ten times as common toward the end of training [8].


A safe and low-cost training environment has recently been created, using pig eyes mounted on a model head. This allows trainee surgeons to track their progress objectively. The pig eyes are infused with diluted fluorescein to trace outflow. Fluorescein can diffuse through the trabecular meshwork, which allows flow speeds to be estimated in non-treated parts of the eye. A disadvantage of this method is that over time, diffusion also takes place through intact vascular endothelium, staining the extravascular space. Fluorescent beads can be used as an alternative, and are suitable in less time-sensitive, more beginner-friendly studies of ablation. However, unlike fluorescein, this method does not account for flow speeds or volume estimates.


There are several surgical steps that can be simulated and practiced for cataract procedures. These include positioning the patient's head, setting up the microscope, gonioscopic visualization of the angle and identification of Schlemm's canal. For the surgery to be performed correctly, the patient's headrest must be close enough to the microscope stand to accommodate the tilted view, and greater distance from it. Trainees can tell their patient that they would like to take a brief look at the angle of the eye. The surgeon should be seated temporally, and the patient's head tilted away by 30 degrees. The microscope should be set up by centering its head, confirming that the tilt knob is covered with a handle. The equipment is then tilted toward the surgeon by 30 degrees. The microscope should be manually lowered, bringing the limbus into focus.


To practice gonioscopic visualization of the angle, the correct handedness of the modified Swan Jacob gonioprism should be confirmed. This is done by placing it on the eye and moving the microscope focus down, toward the nasal angle. The iris root, ciliary body band and trabecular meshwork can be seen through the microscope. They should all be distinguished from Schwalbe's line and the Sampaolesi line. Schlemm's canal should be identified by using a 0.12 forceps to tap lightly on the posterior lip of the primary cataract incision, creating blood reflux. After several seconds, the goniolens should be replaced onto the cornea, to visualize a partially venous, blood-filled Schlemm's canal.


By removing the primary resistance (the trabecular meshwork), aqueous humor can pass more freely into collector channels and aqueous veins. The Goldmann equation states that Intraocular Pressure = [Aqueous Humor Formation/Outflow] + Episcleral Venous Pressure. This equation states that free-flowing aqueous humor should cause intraocular pressure to drop to the same level as in the episcleral veins [26]. However, this is rare, and the average postoperative intraocular pressure is around 16 mmHg [27]. Spectral domain optical coherence tomography can be used to view collector channel diameter change, collapse or patency.


Like human eyes, pig eyes have more outflow along the nasal drainage system than the temporal angle. Trabecular meshwork removal from the nasal can enhance outflow beyond physiological levels. It can also cause fluorescein to flow circumferentially, through small connections between Schlemm's canal-like segments, typical of a pig's angular aqueous plexus [3-5]. Reconstruction of outflow tracts via spectral domain optical coherence tomography have confirmed a correlation between aqueous spaces and collectors where flow was seen. However, these studies have also confirmed the existence of non-perfused vascular structures that could be part of the arterial or venous vascular system, or poorly perfused collector channels.


Recent discoveries have shown valve-like structures that appear to guard collector channel orifices and collapsible aqueous veins  9, 10 . These findings contradict the view that collector channel openings are round and unobstructed. Structural data has shown that flaps are suspended by string-like attachments. This research suggests that these attachments should be maintained during surgery, or that the flaps at the opening of collector channels should be removed. Electron microscopic images of the outer wall suggest that most are removed during trabectome procedures, together with their attachments and the trabecular meshwork [30].


As many patients have both cataract and glaucoma, phacoemulsification is often combined with trabectome surgery, for the cost-effective treatment of both conditions [11]. Combined phaco-trabectome surgery can result in an intraocular pressure reduction of approximately 18% [12]. A recent study of phaco-trabectome surgery patients found the most significant reduction in cases of severe glaucoma, steroid-induced glaucoma [33,34] and pseudoexfoliative glaucoma [13, 14].


Trabectome surgery alone provides an alternative to more invasive procedures. It is suitable for patients who have previously undergone cataract surgery, as well as those who have no visually significant cataract. Studies have shown that lens status or performance of phacoemulsification in the same session has no significant impact on intraocular pressure reduction [38,39].


When comparing patients undergoing trabectome-only with those undergoing phaco-trabectome procedures, research has shown greater benefit in phakic or pseudophakic eyes after phaco-trabectome procedures [40]. However, phakic patients undergoing trabectome showed a greater reduction in intraocular pressure, compared to patients undergoing phacoemulsification combined with trabectome. These results suggest that phacoemulsification may not have a significant impact on intraocular pressure reduction [39].


Historically, angle-based glaucoma surgery in patients with narrow angles was thought more likely to result in synechiae and fibrosis. This was considered a contraindication to trabectome surgery. However, studies of trabectome and phaco-trabectome patients have proven that trabectome surgery can be successful even in these cases. Patients with an angle at Shaffer grade 2 or less (narrow) showed an average intraocular pressure reduction of 42% one year after trabectome surgery, and of 24% one year after phaco-trabectome. Patients with an angle at Shaffer grade 3 or above (open) showed an average intraocular pressure reduction of 37% reduction one year after trabectome surgery, and of 25% reduction one year after phaco-trabectome. These results suggest that trabectome surgery is a viable option for patients with narrow angles [15]


Reoperation after failed trabeculectomy or tube shunt is very challenging. Trabectome surgery is a minimally invasive alternative to a repeat filter or shunt. Studies of patients undergoing trabectome surgery after a failed tube shunt have shown a statistically significant reduction in intraocular pressure after one year [42].


When comparing patients undergoing trabectome surgery after failed trabeculectomy with those undergoing phaco-trabectome, research has shown a greater reduction in intraocular pressure after trabectome than after phaco-trabectome [43]. Further research has shown trabectome surgery after failed trabeculectomy to result in an intraocular pressure reduction of 36%, and a 14% decrease in the number of pressure-lowering medications. 25% of patients were seen to require further surgery [44].


Trabectome surgery has also proven to be a valuable adjuvant at the point of both valved and non-valved tube shunt implantation. When comparing patients undergoing Baerveldt tube implantation alone with those undergoing the same procedure combined with trabectome surgery, both groups showed similar intraocular pressure and visual acuities after the procedures. The combined patients required fewer pressure-lowering drops. These results show that trabectome surgery could improve post-operative quality of life by reducing necessary medication [16]. Results from Ahmed tube implantations showed a similar trend [46].


When trabectome surgery results are correlated with glaucoma severity, patients with more medication, higher intraocular pressure and worse visual field experience a larger reduction in intraocular pressure than those with less aggressive glaucoma [33,37]. Studies have shown patients with the most advanced glaucoma to have a pressure reduction three times greater than those with mild glaucoma. Individuals with advanced glaucoma have been shown to have a lower success rate than those with mild glaucoma. This risk of failure is important when trabectome surgery is considered as a less risky alternative to traditional procedures. Other factors which have been linked to intraocular pressure reduction are age, Hispanic ethnicity, steroid-induced glaucoma and cup disk ratio [37]. Contradictory results have, however, been presented in the cases of ethnicity and the cup disk ratio [17].


The trabectome is very safe, particularly when compared to incisional glaucoma surgery. Recent research has shown the most common complications to include hyphema, peripheral anterior synechiae, corneal injury and temporary spikes in intraocular pressure. Less common complications include transient hypotony lasting less than 3 months, iris injury, cystoid macular edema and cataract progression. There are case reports of a few, rare complications, including cyclodialysis cleft, aqueous misdirection, choroidal hemorrhage and endophthalmitis [18].


1. van der Merwe EL, Kidson SH (2010) Advances in imaging the blood and aqueous vessels of the ocular limbus. Exp Eye Res 91:118–126
2. Polat JK, Loewen NA (2016) Combined phacoemulsification and trabectome for treatment of glaucoma. Surv Ophthalmol.  https://doi.org/10.1016/j.survophthal.2016.03.012
3. Kaplowitz K, Schuman JS, Loewen NA (2014) Techniques and outcomes of minimally invasive trabecular ablation and bypass surgery. Br J Ophthalmol 98:579–585
4. Kaplowitz K, Loewen NA (2013) Minimally Invasive and Nonpenetrating Glaucoma Surgery. In: Yanoff M, S. DJ (eds) Ophthalmology: Expert Consult. Elsevier, pp 1133–1146
5. Christakis PG, Tsai JC, Kalenak JW, et al. (2013) The Ahmed versus Baerveldt study: three-year treatment outcomes. Ophthalmology 120:2232–2240
6. Kaplowitz K, Bussel II, Honkanen R, et al. (2016) Review and meta-analysis of ab-interno trabeculectomy outcomes. Br J Ophthalmol.  Review and meta-analysis of ab-interno trabeculectomy outcomes
7. Kaplowitz K, Abazari A, Honkanen R, Loewen N (2014) iStent surgery as an option for mild to moderate glaucoma. Expert Rev Ophthalmol 9:11–16
8. Martin KR, Burton RL (2000) The phacoemulsification learning curve: per-operative complications in the first 3000 cases of an experienced surgeon. Eye 14 ( Pt 2):190–195
9. Xin C, Wang RK, Song S, et al. (2016) Aqueous outflow regulation: Optical coherence tomography implicates pressure-dependent tissue motion. Exp Eye Res.  https://doi.org/10.1016/j.exer.2016.06.007
10. Johnstone M (2016) 3. Intraocular pressure control through linked trabecular meshwork and collector channel motion. In: Knepper PA, Samples JR (eds) Glaucoma Research and Clinical Advances 2016 to 2018. Kugler Publications, p 41
11. Iordanous Y, Kent JS, Hutnik CM, Malvankar-Mehta MS (2013) Projected Cost Comparison of Trabectome, iStent, and Endoscopic Cyclophotocoagulation Versus Glaucoma Medication in the Ontario Health Insurance Plan. J Glaucoma.  Projected Cost Comparison of Trabectome, iStent, and Endoscopic Cyclophotocoagulation Versus Glaucoma Medication in the Ontario Health Insurance Plan
12. Minckler D, Mosaed S, Dustin L, et al. (2008) Trabectome (trabeculectomy-internal approach): additional experience and extended follow-up. Trans Am Ophthalmol Soc 106:149–59; discussion 159–60
13. Widder RA, Dinslage S, Rosentreter A, et al. (2014) A new surgical triple procedure in pseudoexfoliation glaucoma using cataract surgery, Trabectome, and trabecular aspiration. Graefes Arch Clin Exp Ophthalmol 252:1971–1975
14. Ting JLM, Damji KF, Stiles MC, Trabectome Study Group (2012) Ab interno trabeculectomy: outcomes in exfoliation versus primary open-angle glaucoma. J Cataract Refract Surg 38:315–323
15. Bussel II, Kaplowitz K, Schuman JS, et al. (2015) Outcomes of ab interno trabeculectomy with the trabectome by degree of angle opening. Br J Ophthalmol 99:914–919
16. Knowlton P, Bilonick R, Loewen N (2016) Baerveldt tube shunts with trabectome surgery in a matched comparison to Baerveldt tube shunts
17. Roy P, Loewen RT, Dang Y, et al. (2016) Stratification of phaco-trabectome surgery results using a glaucoma severity index
18. Kaplowitz K, Bussel II, Honkanen R, et al. (2016) Review and meta-analysis of ab-interno trabeculectomy outcomes. Br J Ophthalmol 100:594–600


Trabeculectomy  is a surgical procedure used in the treatment of  glaucoma  to relieve  intraocular pressure  by removing part of the  eye 's  trabecular meshwork  and adjacent structures. It is the most common  glaucoma surgery  performed and allows drainage of  aqueous humor  from within the eye to underneath the conjunctiva where it is absorbed. This outpatient procedure was most commonly performed under monitored anesthesia care using a  retrobulbar block  or  peribulbar block  or a combination of topical and subtenon ( Tenon's capsule ) anesthesia. Due to the higher risks associated with bulbar blocks, topical analgesia with mild sedation is becoming more common. Rarely general anesthesia will be used, in patients with an inability to cooperate during surgery.


An initial pocket is created under the conjunctiva and Tenon's capsule and the wound bed is treated for several seconds to minutes with  mitomycin C  (MMC, 0.5–0.2 mg/ml) or  5-fluorouracil  (5-FU, 50 mg/ml) soaked sponges. These chemotherapeutics help to prevent failure of the filter bleb from scarring by inhibiting fibroblast proliferation. Alternatively, non-chemotherapeutic adjuvants can be implemented to prevent super scarring by wound modulation, such as the ologen collagen matrix implant. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ]  Some surgeons prefer "fornix-based" conjunctival  incisions while others use "limbus-based" construction at the corneoscleral junction which may allow easier access in eyes with deep sulci.
A partial thickness flap with its base at the corneoscleral junction is then made in the sclera after careful cauterization of the flap area, and a window opening is created under the flap with a Kelly-punch to remove a portion of the  sclera ,  Schlemm's canal  and the  trabecular meshwork  to enter the  anterior chamber .
Because of the fluid egress the iris will partially prolapse through the sclerostomy and is usually therefore grasped to perform an excision called  iridectomy . This iridectomy will prevent future blockage of the sclerostomy. The scleral flap is then sutured loosely back in place with several sutures. The conjunctiva is closed in a watertight fashion at the end of the procedure. [ citation needed ]


Intraocular pressure  may be lowered by allowing drainage of aqueous humor from within the eye to the following routes: (1) filtration through the sclerotomy around the margins of the scleral flap into the filtering bleb that forms underneath the conjunctiva, (2) filtration through outlet channels in the scleral flap to underneath the conjunctiva,(3) Filtration through the connective tissue of the scleral flap to underneath the conjunctiva. Into cut ends of Schlemm's canal. (4) aqueous flow into cut ends of Schlemm's canal into collector channels and episcleral veins  (5) into a cyclodialysis cleft between the  ciliary body  and the sclera if tissue is dissected posterior to the scleral spur. [ citation needed ]


Glaucoma medications are usually discontinued to improve aqueous humor flow to the bleb. Topical medications consist typically of antibiotic drops four times per day and anti-inflammatory therapy e.g. with prednisolone drops every two hours. A shield is applied to cover the eye until anesthesia has worn off (that also anesthetizes the optic nerve) and vision resumes.


Patients are instructed to call immediately for pain that cannot be controlled with over the counter pain medication or if vision decreases, to not rub the eye and to wear the shield at night for several days after surgery.


If 5-FU was used during surgery or if no anti-fibrotic agent was applied, 5 mg 5-FU daily can be injected in the 7–14 postoperative days. In the following days to weeks sutures that hold the scleral flap down can be cut by laser suture lysis to titrate the intraocular pressure down by improving outflow. In laser suture lysis a red light laser and a contact lens are used to penetrate noninvasively the overlying conjunctiva and cut the black nylon suture. Some surgeons prefer adjustable flap sutures during the trabeculectomy that can be loosened later on with forceps in a slit lamp office procedure.


Trabeculectomy is the most common invasive  glaucoma surgery . It is highly effective in the treatment of advanced glaucoma as demonstrated in major  glaucoma  studies. [ citation needed ]  Even if a prior trabeculectomy has failed a second trabeculectomy can be performed at a different site. If scarring is the main reason, anti-fibrotic and anti-inflammatory therapy has to be intensified in the second procedure. Alternatively, insertion of a  glaucoma valve  device can be used.


Trabeculectomy has undergone numerous modifications, e.g. filtering trepanotrabeculectomy (TTE), a modification of the operation after J. Fronimopoulos. A triangular scleral flap is created which is approximately one-half as thick as the sclera. Trepanation is performed with a 2 mm trephine. The scleral edge of the trepanation opening is heat-cauterized. [ 8 ]


Additional deep scleral dissection can also be performed in the scleral bed with trabeculectomy, first introduced by T. Dada et al.; [ 9 ]  deep scleral excision is performed in non-penetrating filtering surgeries but not traditionally in trabeculectomy. The space created from the deep scleral dissection is proposed to accommodate certain biocompatible spacer or devices in order to prevent subscleral fibrosis and to maintain good filtering results in this modified operation.


Various devices have been used with trabeculectomy techniques with the goal of improving safety of the procedure, maintaining drainage of aqueous humor, and to maintain the patency of bleb. [ 10 ]  Examples of Trabeculectomy-modifying devices are Ex-PRESS, Gelfilm, XEN Gel stent,  antifibrotic  materials (e.g Ologen), ePTFE (expanded  polytetrafluoroethylene ) membrane and PreserFlo MicroShunt. Comparing each of these devices for effectiveness and safety is required. [ 10 ]  There is some low-quality evidence that usage of Ex-PRESS implant, a miniature stainless steel shunt, and human amniotic membrane as adjuncts with trabeculectomy have been associated with reduced intraocular pressure in patients after a one-year follow-up, compared to standard trabeculectomy. [ 10 ]  In addition, the PreserFlo MicroShunt may help prevent complications such as postoperative hypotony or bleb leakage; however, this technique may have a lower effectiveness at reducing  intraoculur pressure  compared to a standard trabeculectomy procedures. [ 10 ]


Further research is needed to compare the effectiveness of trabeculectomy techniques. It is not clear if a fornix-based surgical approach has a different safety rating, complication rate, surgical failure rate, or effectiveness compared to a limbal-based conjunctival flaps technique. [ 11 ]


Currently, there are no published trials which compare the efficacy and safety of  ab interno trabeculectomy with Trabectome  with other procedures for treating glaucoma. [ 12 ]  The first trial to do so is the TAGS randomised controlled trial which investigated if eye drops or trabeculectomy is more effective in treating advanced primary open-angle glaucoma. After two years researchers found that vision and quality of life are similar in both treatments. At the same time eye pressure was lower in people who underwent surgery and in the long-run surgery is more cost-effective. [ 13 ] [ 14 ]


Peter Gordon Watson  and John Cairns developed the trabeculectomy procedure in the 1970s. [ 15 ]


Trabeculoplasty  is a laser treatment for glaucoma. It is done on an argon laser equipped slit lamp, using a Goldmann gonioscope lens mirror. Specifically, an argon laser is used to improve drainage through the eye's  trabecular meshwork , from which the  aqueous humour  drains. This helps reduce  intraocular pressure  caused by  open-angle glaucoma . [ 1 ]


The LiGHT trial compared the effectiveness of eye drops and selective laser trabeculoplasty for open angle glaucoma. Both contributed to a similar quality of life but most people undergoing laser treatment were able to stop using eye drops. Laser trabeculoplasty was also shown to be more cost-effective. [ 2 ]


Vitrectomy  is a surgery to remove some or all of the  vitreous humor  from the  eye .


Anterior vitrectomy  entails removing small portions of the vitreous humor from the front structures of the eye—often because these are tangled in an intraocular lens or other structures.


Pars plana  vitrectomy  is a general term for a group of operations accomplished in the deeper part of the eye, all of which involve removing some or all of the vitreous humor—the eye's clear internal jelly.


Even before the modern era, some surgeons performed crude vitrectomies. For instance, Dutch surgeon Anton Nuck (1650–1692) claimed to have removed vitreous by suction in a young man with an inflamed eye. [ 1 ]  In Boston,  John Collins Warren  (1778–1856) performed a crude limited vitrectomy for angle closure  glaucoma . [ 2 ]


Options for  anesthesia  for vitrectomy are  general anaesthesia ,  local anesthesia ,  topical anesthesia  and  intracameral   lidocaine  irrigation. [ medical citation needed ]