moon blindness

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Recurrent inflammation of a horse's eyes, often resulting in eventual blindness. Also called mooneye.

Century Dictionary and Cyclopedia

1. n. Same as moon-blink.
2. n. An eye-disease of the horse, scientifically known as periodic ophthalmia, the cause of which is unknown. One attack is followed at regular intervals by others which finally produce total blindness in one or both eyes.

Wiktionary

1. n. A chronic equine inflammatory eye disease.
2. n. The optic condition night blindess: reduced eyesight in faint light.

GNU Webster's 1913

1. n. (Far.), (Med.) Hemeralopia.

WordNet 3.0

1. n. recurrent eye inflammation in horses; sometimes resulting in blindness
2. n. inability to see clearly in dim light; due to a deficiency of vitamin A or to a retinal disorder