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Corneal Dystrophy, Epithelial Basement Membrane
The clinical appearance of the cornea in this disorder is non-specific with features found in as many as 75% of older individuals who do not have a corneal dystrophy. Some of the clinical findings are also found in other dystrophies such as Meesmann (122100), Reis-B√ºcklers (608470), Lisch dystrophy (300778), lattice type I (122200), and Thiel-Behnke (602082). The common feature in all these is the formation of microcysts in the epithelium with alterations in the basement membrane. The pattern is sometimes described as a map-dot-fingerprint dystrophy. Corneal erosions occur in all to some degree and vision is minimally impacted. Many patients are asymptomatic unless corneal erosions occur.
Hereditary Cogan microcystic corneal dystrophy is sometimes diagnosed in the first decade of life but more characteristically found in people over the age of 30. The corneal changes wax and wane and are highly variable between patients. The dots consist of pseudocysts filled with intracellular debris while the geographic patterns are generated by multilayered basement membrane extensions into the epithelium. The rupture of these cysts results in corneal erosions. The underlying defect likely consists of defects in hemidesmosomal junctions.
No systemic disease is associated with this corneal dystrophy.
Many individuals with some findings of microcystic dystrophy have no family history of the disease and, as noted above, these are common in older people. However, autosomal dominant pedigrees have been reported with typical corneal lesions among family members of all ages. Several point mutations in the TGFBI gene on chromosome 5 (5q31) have been found but this likely accounts for only a small proportion of cases. Mutations in the same gene have been found in other corneal dystrophies as well (lattice dystrophy I, granular dystrophy, Thiel-Behnke dystrophy, Reis-Bucklers, and combined lattice-granular dystrophy or Avellino type).
Genomic studies will likely clarify the current confusing nosology.
Most patients require no treatment. Persistent epithelial erosions can be treated with hypertonic solutions or bandage lenses.