Corneal dystrophy, Cogan: A disorder in which the cornea (the normally clear front window of the eye) shows grayish fingerprint lines, geographic map-like lines, and dots (or microcysts) on examination with a slit-lamp that focuses a high intensity light beam as a slit while the examiner looks at the front of the eye through a magnifying scope.

The disorder is usually silent and without symptoms. However, about one patient in ten has recurrent erosion of the cornea that usually begins after the age 30.

Conversely, half of patients with recurrent corneal erosions of idiopathic (unknown) origin have this disorder.

Under the microscope, a structure called the epithelial basement membrane is abnormal. The disorder is therefore sometimes called epithelial basement corneal dystrophy.

The disorder was first described by Cogan and colleagues in 1964. Hence, the name: Cogan corneal dystrophy. It is also known descriptively (to add to the confusion) as map-dot-fingerprint type corneal dystrophy and microcystic corneal dystrophy.