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Meesmann corneal dystrophy
Meesmann corneal dystrophy (MECD) is a rare form of superficial corneal dystrophy characterized by distinct tiny bubble-like, round-to-oval punctate bilateral opacities in the central corneal epithelium, and to a lesser extent in the peripheral cornea, with little impact on vision.
Prevalence of this form of corneal dystrophy is not known as a registry of affected cases does not exist. Numerous cases have been reported from Denmark, Germany, Japan, USA, Saudi Arabia and Poland.
Lesions develop during infancy. MECD often remains asymptomatic until middle age, when intermittent, mild ocular irritation, photophobia, transient blurred vision, and irregular astigmatism develop. The condition persists throughout life. In severe cases, subepithelial scarring produces a slight grayish central corneal opacification. Corneal sensitivity is normal.
Meesmann corneal dystrophy is caused by a mutation in one of a pair of genes, KRT3 (12q13.13) or KRT12 (17q11-q1) that encode the two units of cytokeratin in the corneal epithelium. Stocker-Holt corneal dystrophy is a variant of MECD caused by a p. Arg19Leu amino acid change in cytokeratin 12.
Light microscopy reveals intraepithelial cysts and the epithelium may be thickened and disorganized. Histopathologically, MECD is characterized by intraepithelial cysts at different levels in the corneal epithelium, which is irregular in thickness.
Suspected cases of MECD should be differentiated from other disorders of the corneal epithelium, such as vapor spray keratitis, mild epithelial edema and the bleb pattern of epithelial basement membrane dystrophy. MECD and Lisch epithelial corneal dystrophy (LECD, see this term) have clinical similarities but are easily distinguished from one another by the different modes of inheritance, i.e. autosomal dominant versus X-linked recessive.
MECD has an autosomal dominant pattern of inheritance.
Management and treatment
Removal of the abnormal corneal epithelium has been used to treat MECD, but this approach is not curative as the dystrophy recurs in the regenerated epithelium.