Corneal dystrophy, Cogan: A disorder in which the cornea shows grayish fingerprint lines, geographic map-like lines, and dots (or microcysts). These lines and dots can be seen on examination with a slit-lamp, which focuses a high-intensity light beam through a slit while the examiner uses a magnifying scope to look at the front of the eye where the epithelial basement membrane is seen as abnormal. The disorder is usually without symptoms. However, about 1 patient in 10 has recurrent erosion of the cornea that generally begins after age 30. Also known as epithelial basement corneal dystrophy and map-dot-fingerprint type corneal dystrophy and microcystic corneal dystrophy.