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ERROR: type should be string, got "https://profreg.medscape.com/px/getpracticeprofile.do?method=getProfessionalProfile&urlCache=aHR0cHM6Ly9lbWVkaWNpbmUubWVkc2NhcGUuY29tL2FydGljbGUvMTE5NjIxMi1vdmVydmlldw==\nDrugs & Diseases > Ophthalmology\nSchnyder Corneal Dystrophy\nAuthor: Ahmed Farghaly Abdelhameed Omar, MD, PhD; Chief Editor: Hampton Roy, Sr, MD more...\nSections Schnyder Corneal Dystrophy\nSchnyder corneal dystrophy (SCD), also called Schnyder crystalline corneal dystrophy (SCCD), is a rare autosomal-dominant stromal dystrophy that is characterized by bilateral corneal opacification, resulting from an abnormal accumulation of cholesterol and lipid. The causative gene for this disease is UBIAD1, which is present on 1p36. The gene is involved in cholesterol metabolism.\nPlease refer to the image below depicting the natural history of Schnyder corneal dystrophy specific to age.\nThe natural history of Schnyder dystrophy with age. Weiss JS: Schnyder's dystrophy of the cornea: a Swede-Finn connection. Cornea 1992; 11(2): 93-101.\nView Media Gallery\nVan Went and Wibaut first described crystalline dystrophy in the Dutch literature in 1924, and it was delineated further by Schnyder in the Swiss literature in 1929. [1, 2]\nWhile the incidence in the general population is unknown, the world's largest pedigree (>200 patients with Schnyder corneal dystrophy) has a Swede-Finn heritage and has been traced to the southwest coast of Finland on the Bay of Bothnia. However, the dystrophy has been reported in other ethnicities and in all racial groups.\nThe pathogenesis remains unknown, but it is postulated to result from a localized defect of lipid metabolism. It has been demonstrated in affected corneas versus normal corneas that the cholesterol content increases 10-fold and the phospholipid content increases 5-fold. Immunohistochemical analysis has revealed the preferential deposition of apolipoprotein components of high-density lipoprotein (HDL), that is, apoA I, apoA II, and apoC, but not of low-density lipoprotein (LDL), that is, apoB. This finding suggests an abnormal metabolism of HDL in the cornea with Schnyder corneal dystrophy.\nThe discovery of the causative gene, UBIAD1 (UbiA prenyltransferase domain-containing protein-1), will be the link to further understanding of this disease. The gene produces a protein that contains a prenyltransferase domain that could play a role in cholesterol metabolism. In addition, UBIAD1 interacts with the C-terminal portion of apolipoprotein E (apoE), which is known to help mediate cholesterol removal from the cells. Further research will determine whether the excess cholesterol results from increased cholesterol production or decreased removal.\nThe dystrophy has been reported in the United States, although the incidence in the general population is unknown.\nWhile the incidence is unknown, the dystrophy has been reported in eastern and western Europe, Taiwan, Japan, and Turkey.\nMortality/Morbidity\nA long-term study of 34 families over a period of 18 years revealed that most morbidity derives from progressive corneal clouding, leading to glare and decreased vision in daylight. [3]\nIn this study, mean Snellen uncorrected visual acuity (UCVA) was between 20/25 and 20/30 in patients younger than 40 years and between 20/30 and 20/40 in patients aged 40 years or older. Scotopic vision remained relatively good until later in life, when corneal opacification increased.\nStudies of those affected reveal that 54% of patients aged 50 years and older and 77% of patients aged 70 years and older had corneal transplant surgery. Although study numbers are small, there is no evidence of increased mortality from cardiovascular disease in Schnyder corneal dystrophy. Of note, however, 71% of patients who had corneal transplant surgery reported the use of cholesterol-lowering agents. This was not statistically different from those patients who had not undergone corneal transplant surgery.\nSchnyder corneal dystrophy can occur in whites, Asians, and African Americans.\nAlthough rare sporadic cases have been reported, Schnyder corneal dystrophy is primarily an autosomal dominant disease, affecting both sexes with equal probability.\nThe disease may appear as early as the first decade of life and slowly progresses with age. However, a diagnosis may be delayed until the fourth decade in patients with corneal opacification without crystalline deposits.\nResults of clinical examination have shown that crystalline deposits are present in only 51% of patients with Schnyder corneal dystrophy. [4]\nWhile Schnyder corneal dystrophy may be diagnosed easily during the first decade of life, the diagnosis Schnyder corneal dystrophy sine crystals is more challenging and is reported to be delayed up to the fourth decade of life. Some patients have been documented to have unilateral crystalline deposition. Why the corneal cholesterol forms crystals in some patients, but not in others, remains unclear.\nContrary to prior reports, many patients with Schnyder corneal dystrophy eventually require corneal transplantation because of glare and decreased vision in daylight.\nFor excellent patient education resources, visit eMedicineHealth's Cholesterol Center. Also, see eMedicineHealth's patient education articles High Cholesterol, Cholesterol FAQs, and Atorvastatin (Lipitor).\nVan Went JM, Wibaut F. Een zyeldzame erfelijke hoornvliesaandoening. Ned Tijdschr Geneeskd. 1924. 68(B):2996-2997.\nSchnyder WF. Mitteilung uber einen neuen Typus von familiarer hornhauterkrankung. Schweiz Med Wochenschr. 1929. 59:559-571.\nWeiss JS. Visual morbidity in thirty-four families with Schnyder crystalline corneal dystrophy (an American Ophthalmological Society thesis). Trans Am Ophthalmol Soc. 2007. 105:616-48. [Medline].\nWeiss JS, Møller HU, Aldave AJ, Seitz B, Bredrup C, Kivelä T, et al. IC3D classification of corneal dystrophies--edition 2. Cornea. 2015 Feb. 34 (2):117-59. [Medline].\nWeiss JS, Khemichian AJ. Differential diagnosis of Schnyder corneal dystrophy. Dev Ophthalmol. 2011. 48:67-96. [Medline].\nPaparo LG, Rapuano CJ, Raber IM, Grewal S, Cohen EJ, Laibson PR. Phototherapeutic keratectomy for Schnyder's crystalline corneal dystrophy. Cornea. 2000 May. 19 (3):343-7. [Medline].\nBron AJ. Corneal changes in the dislipoproteinaemias. Cornea. 1989. 8(2):135-40. [Medline].\nBron AJ, Williams HP, Carruthers ME. Hereditary crystalline stromal dystrophy of Schnyder. I. Clinical features of a family with hyperlipoproteinaemia. Br J Ophthalmol. 1972 May. 56(5):383-99. [Medline].\nDelleman JW, Winkelman JE. Degeneratio corneae cristallinea hereditaria. A clinical, genetical and histological study. Ophthalmologica. 1968. 155(5):409-26. [Medline].\nFreddo TF, Polack FM, Leibowitz HM. Ultrastructural changes in the posterior layers of the cornea in Schnyder's crystalline dystrophy. Cornea. 1989 Sep. 8(3):170-7. [Medline].\nGaynor PM, Zhang WY, Weiss JS, et al. Accumulation of HDL apolipoproteins accompanies abnormal cholesterol accumulation in Schnyder's corneal dystrophy. Arterioscler Thromb Vasc Biol. 1996 Aug. 16(8):992-9. [Medline].\nGibbels E, Schaefer HE, Runee U, et al. Severe polyneuropathy in Tangier disease mimicking syringomyelia or leprosy. Clinical, biochemical, electrophysiological, and morphological evaluation, including electron microscopy of nerve, muscle, and skin biopsies. J Neurology. 1985. 232(5):283-294. [Medline].\nGjone E. Familial lecithin cholesterol acyltransferase (LCAT) deficiency. Birth Defects Orig Artic Ser. 1982. 18(6):423-31. [Medline].\nHoang-Xuan T, Pouliquen Y, Gasteau J. [Schnyder's crystalline dystrophy. II. Association with genu valgum]. J Fr Ophtalmol. 1985. 8(11):743-7. [Medline].\nMcCarthy M, Innis S, Dubord P, et al. Panstromal Schnyder corneal dystrophy. A clinical pathologic report with quantitative analysis of corneal lipid composition. Ophthalmology. 1994 May. 101(5):895-901. [Medline].\nOrr A, Dube MP, Marcadier J, et al. Mutations in the UBIAD1 gene, encoding a potential prenyltransferase, are causal for Schnyder crystalline corneal dystrophy. PLoS ONE. 2007 Aug 1. 2(1):e685. [Medline].\nPhilipson BT. Fish eye disease. Birth Defects Orig Artic Ser. 1982. 18(6):441-8. [Medline].\nRodrigues MM, Kruth HS, Krachmer JH, et al. Unesterified cholesterol in Schnyder's corneal crystalline dystrophy. Am J Ophthalmol. 1987 Aug 15. 104(2):157-63. [Medline].\nTheendakara V, Tromp G, Kuivaniemi H, et al. Fine mapping of the Schnyder's crystalline corneal dystrophy locus. Hum Genet. 2004 May. 114(6):594-600. [Medline].\nVesaluoma MH, Linna TU, Sankila EM, et al. In vivo confocal microscopy of a family with Schnyder crystalline corneal dystrophy. Ophthalmology. 1999 May. 106(5):944-51. [Medline].\nWeiss JS. Schnyder crystalline dystrophy sine crystals. Recommendation for a revision of nomenclature. Ophthalmology. 1996 Mar. 103(3):465-73. [Medline].\nWeiss JS. Schnyder's dystrophy of the cornea: a Swede-Finn connection. Cornea. 1992 Mar. 11(2):93-101. [Medline].\nWeiss JS, Kruth HS, Kuivaniemi H, et al. Mutations in the UBIAD1 gene on chromosome short arm 1, region 36, cause Schnyder crystalline corneal dystrophy. Invest Ophthalmol Vis Sci. 2007 Nov. 48(11):5007-12. [Medline].\nWeiss JS, Rodrigues MM, Kruth HS, et al. Panstromal Schnyder's corneal dystrophy. Ultrastructural and histochemical studies. Ophthalmology. 1992 Jul. 99(7):1072-81. [Medline].\nWeller RO, Rodger FC. Crystalline stromal dystrophy: histochemistry and ultrastructure of the cornea. Br J Ophthalmol. 1980 Jan. 64(1):46-52. [Medline].\nWu CW, Lin PY, Liu YF, et al. Central corneal mosaic opacities in Schnyder's crystalline dystrophy. Ophthalmology. 2005 Apr. 112(4):650-3. [Medline].\nWeiss JS. Schnyder corneal dystrophy. Curr Opin Ophthalmol. 2009 Jul. 20 (4):292-8. [Medline].\nA 22-year-old woman with circular corneal opacity best seen in retroillumination. Weiss JS: Schnyder's dystrophy of the cornea: a Swede-Finn connection. Cornea 1992; 11(2): 93-101.\nA 20-year-old woman with ringlike deposition of anterior stromal cholesterol crystals. Weiss JS: Schnyder's dystrophy of the cornea: a Swede-Finn connection. Cornea 1992; 11(2): 93-101.\nA 37-year-old man with central disclike opacity, affecting the entire stromal thickness, anterior stromal cholesterol crystals, and peripheral arcus lipoides. Weiss JS: Schnyder's dystrophy of the cornea: a Swede-Finn connection. Cornea 1992; 11(2): 93-101.\nA 78-year-old woman with dense arcus lipoides in the corneal periphery, sparing the corneal scleral limbus. Weiss JS: Schnyder's dystrophy of the cornea: a Swede-Finn connection. Cornea 1992; 11(2): 93-101.\nAhmed Farghaly Abdelhameed Omar, MD, PhD Assistant Professor of Ophthalmology, Department of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine; Ophthalmologist/Cornea Specialist, University Hospitals Eye Institute, University Hospitals Cleveland Medical Center\nAhmed Farghaly Abdelhameed Omar, MD, PhD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery, Egyptian Medical Syndicate, Egyptian Ophthalmological Society, European Society of Cataract and Refractive Surgery, International Society of Refractive Surgery\nDaniel C Daroszewski, MD Resident Physician, Department of Ophthalmology, University Hospitals Eye Institute, Case Western Reserve University School of Medicine\nSimon K Law, MD, PharmD Clinical Professor of Health Sciences, Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, David Geffen School of Medicine\nSimon K Law, MD, PharmD is a member of the following medical societies: American Academy of Ophthalmology, Association for Research in Vision and Ophthalmology, American Glaucoma Society\nChristopher J Rapuano, MD Professor, Department of Ophthalmology, Sidney Kimmel Medical College of Thomas Jefferson University; Director of the Cornea Service, Wills Eye Hospital\nChristopher J Rapuano, MD is a member of the following medical societies: American Academy of Ophthalmology, American Ophthalmological Society, American Society of Cataract and Refractive Surgery, Contact Lens Association of Ophthalmologists, Cornea Society, Eye Bank Association of America, International Society of Refractive Surgery\nDisclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: AAO; OMIC; Bio-Tissue; Dompe; Glaukos; Novartis; Sun Ophthalmics; TearLab<br/>Serve(d) as a speaker or a member of a speakers bureau for: Glaukos; Dompe; Bio-Tissue; Novartis<br/>Received income in an amount equal to or greater than $250 from: AAO; OMIC; Bio-Tissue; Dompe; Glaukos; Novartis; Sun Ophthalmics; TearLab.\nHampton Roy, Sr, MD Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences\nHampton Roy, Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, Pan-American Association of Ophthalmology\nFernando H Murillo-Lopez, MD Senior Surgeon, Unidad Privada de Oftalmologia CEMES\nFernando H Murillo-Lopez, MD is a member of the following medical societies: American Academy of Ophthalmology\nJayne S Weiss, MD Professor of Ophthalmology, Director of Refractive Surgery, Kresge Eye Institute, Wayne State University School of Medicine\nJayne S Weiss, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Ophthalmology, American Ophthalmological Society, Association for Research in Vision and Ophthalmology, Eye Bank Association of America, Phi Beta Kappa\nBrad Spagnolo, MD\nBrad Spagnolo, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery\nencoded search term (Schnyder Corneal Dystrophy) and Schnyder Corneal Dystrophy\nPrimary Congenital Glaucoma\nAnterior Segment and Fundus Photography\nCaroticocavernous Fistula\nPostoperative Corneal Edema\nCornea and External Disease\nSubconjunctival Microinvasive Glaucoma Surgeries\nPenetrating Keratoplasty Effective for Corneal Complications of Shingles\nOcular Trauma: 8 Potentially Devastating Eye Injuries\nAccording to Ophthalmologists\nKeeping Eyes Safe From COVID-19: What Works?\nDrug-Induced Maculopathy\nNeuro-Ophthalmic Manifestations of Coronavirus Disease 19\nEndophthalmitis After Cataract Surgery: An Update on Recent Advances\nPilocarpine Promising as Presbyopia Treatment\n2001 /viewarticle/944090 News\nNews Secondary Sjogren's Syndrome, Scleritis Linked to Corneal Complications\n2003 /viewarticle/941448 Journal Article\nAssessing Solid Organ Donors and Monitoring Transplant Recipients for Human Immunodeficiency Virus, Hepatitis B Virus, and Hepatitis C Virus Infection — U.S. Public Health Service Guideline, 2020 2.0 CME / CE / ABIM MOC Credits Journal Article\n2.0 CME / CE / ABIM MOC\nAssessing Solid Organ Donors and Monitoring Transplant Recipients for Human Immunodeficiency Virus, Hepatitis B Virus, and Hepatitis C Virus Infection — U.S. Public Health Service Guideline, 2020\nNews Outdoor Intraocular Pressure Screening Clinic Boosts Patient Management During Pandemic\n2001 http://www.medscape.com/resource/cornea-external-disease"