Crystalline Dystrophy

Author: Jayne S Weiss, MD; Chief Editor: Hampton Roy Sr, MD more...

Updated: Nov 28, 2011

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Background
Pathophysiology
Epidemiology
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Background

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.

Please refer to the image below depicting the natural history of schnyder crystalline corneal dystrophy (SCCD) specific to age.

The 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.

Van 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]}

While the incidence in the general population is unknown, the world's largest pedigree (>200 patients with SCCD) 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.

Pathophysiology

The 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 SCCD.

The recent discovery of the causative gene, UBIAD1, 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.

Frequency

United States

The dystrophy has been reported in the United States, although the incidence in the general population is unknown.

International

While the incidence is unknown, the dystrophy has been reported in eastern and western Europe, Taiwan, Japan, and Turkey.

Mortality/Morbidity

A long-term study of 33 families over a period of 18 years reveals that most morbidity derives from progressive corneal clouding, leading to glare and decreased vision in daylight.

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. Nevertheless, while scotopic vision remained relatively good, increasing corneal opacification with age resulted in decreased scotopic vision.

Studies 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 SCCD. 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.

Race

SCCD can occur in whites, Asians, and African Americans.

Sex

Although rare sporadic cases have been reported, SCCD is primarily an autosomal dominant disease, affecting both sexes with equal probability.

Age

The 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.

Proceed to Clinical Presentation

Contributor Information and Disclosures

Author

Jayne S Weiss, MD Professor of Ophthalmology, Director of Refractive Surgery, Kresge Eye Institute, Wayne State University

Jayne 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, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Coauthor(s)

Brad Spagnolo, MD Ophthalmology, Baltimore-Washington Eye Center

Brad Spagnolo, MD is a member of the following medical societies: American Academy of Ophthalmology and American Society of Cataract and Refractive Surgery

Disclosure: Nothing to disclose.

Specialty Editor Board

Fernando H Murillo-Lopez, MD Senior Surgeon, Unidad Privada de Oftalmologia CEMES

Fernando H Murillo-Lopez, MD is a member of the following medical societies: American Academy of Ophthalmology

Disclosure: Nothing to disclose.

Simon K Law, MD, PharmD Associate Professor of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, David Geffen School of Medicine

Simon K Law, MD, PharmD is a member of the following medical societies: American Academy of Ophthalmology, American Glaucoma Society, and Association for Research in Vision and Ophthalmology

Disclosure: Nothing to disclose.

Christopher J Rapuano, MD Professor, Department of Ophthalmology, Jefferson Medical College of Thomas Jefferson University; Director of the Cornea Service, Co-Director of Refractive Surgery Department, Wills Eye Institute

Christopher J Rapuano, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery, Contact Lens Association of Ophthalmologists, Cornea Society, Eye Bank Association of America, International Society of Refractive Surgery, and Pan-American Association of Ophthalmology

Disclosure: Allergan Honoraria Speaking and teaching; Allergan Consulting fee Consulting; Alcon Honoraria Speaking and teaching; Inspire Honoraria Speaking and teaching; RPS Ownership interest Other; Vistakon Honoraria Speaking and teaching; EyeGate Pharma Consulting; Inspire Consulting fee Consulting; Bausch & Lomb Honoraria Speaking and teaching; Bausch & Lomb Consulting fee Consulting

Lance L Brown, OD, MD Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri

Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy Sr, MD Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences

Hampton Roy Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, and Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.

References

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A 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.

A 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.

A 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.

A 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.