Summary

Corneal dystrophies are a group of progressive disorders involving abnormal, usually bilateral deposition of substances in the cornea, which can eventually opacify the cornea and obstruct vision. Underlying genetic abnormalities have been identified for most corneal dystrophies, and most are hereditary.

Background

Over 20 corneal dystrophies exist, which affect all parts of the cornea and are categorised by anatomical location.

The many corneal dystrophies share several traits:

• They are usually hereditary
• They can occur in otherwise healthy people
• Disease is bilateral
• Most progress gradually
• They usually begin in one of the five layers of the cornea (epithelium, Bowman’s layer, stromal, Descemet’s membrane, endothelium), and may later spread to nearby layers

Some corneal dystrophies cause severe visual impairment, whilst others cause mild or no visual problems, and are diagnosed incidentally during an eye examination. Common features of disease that has progressed are recurrent corneal erosions, blurring of vision and reduced corneal sensation.

Epithelial dystrophies

Cogan (epithelial basement membrane) dystrophy

• The commonest corneal epithelial dystrophy
• Inheritance: usually sporadic, occurring without a family history. Rarely, it can be inherited (autosomal dominant, AD) and involve the TGFB1 gene

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Mutations in the TGFB1 gene, which encodes ‘transforming growth factor beta induced’, causes several forms of corneal dystrophies. Other than Reis-Buckler’s dystrophy, TGFB1 mutations are found in: epithelial basement membrane dystrophy; Thiel-Behnke dystrophy; granular corneal dystrophy; and lattice corneal dystrophy.

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• Histology: thickening of the basement membrane, deposition of fibrillary protein between the basement membrane and Bowman layer
• Presentation: onset typically during teenage years; 〜1/10 patients develop corneal erosions in their 20s; the remainder remain asymptomatic
• Lesions are best visualised by retroillumination on slit-lamp or scleral scatter. The following signs are characteristic: “fingerprint-like” subepithelial ridges; “map-like” subepithelial opacities; and “dot-like” intraepithelial cysts.