The central cornea is usually of normal thickness, and the epithelium overlying the area of thinning is intact. Both eyes usually are affected, but the degree of involvement may be asymmetric. The area of thinning typically is epithelialized, clear, avascular, and without lipid deposits. On careful slit lamp evaluation, prominent lymphatics often are detected at the inferior limbus parallel to the area of thinning. Computerized videokeratography is extremely useful in detecting and diagnosing early disease, which may not be readily detectable on slit lamp evaluation.
Histological examination shows an area of thinning that is epithelialized, clear, and avascular.
Stroma is thinned, and the Bowman layer may have breaks or may be completely absent in the affected area. Typically, lipid deposits are absent, and normal appearing endothelium and the Descemet membrane are present. In acute hydrops, breaks in the Descemet membrane with swelling of the stroma and inflammatory cell infiltrate may be seen. Spectacle correction usually fails early in the course of this disease as the degree of irregular astigmatism increases. Rigid gas permeable contact lenses provide excellent oxygen transmission to the cornea but are harder to fit.