Fleischer ring

Fleischer rings are pigmented rings in the peripheral cornea, resulting from iron deposition in basal epithelial cells. They are usually yellowish to dark-brown, and may be complete or broken.

Fleischer rings are indicative of keratoconus, a degenerative corneal condition that causes the cornea to thin and change to a conic shape.

Confusion with Kayser-Fleischer rings
Some confusion exists between Fleischer rings and Kayser-Fleischer rings. Kayser-Fleischer rings are caused by copper deposits, and are indicative of Wilson's disease, whereas Fleischer rings are caused by iron deposits.