Cataracts are clouding of the eye's natural lens. They can affect one or both of the eyes. Since the lens in a healthy eye is clear like a camera lens, light has no problem passing through the lens to the back of the eye to the retina where images are processed. When a cataract is present, the light cannot get through the lens as easily and, as a result, chickens often become blind
There are several different causes of cataracts in chickens:
- Genetics: Chickens of the Light and Dark Brahma breed are predisposed to developing cataracts. In 1991, one study revealed that 69% of the cockerels and 15% of the pullets in an inbred flock of approximately 200 dark and light Brahma chickens had cataracts in one or both of their eyes, and crooked toes; the chickens had been normal until all of a sudden at six months of age they developed cataracts, with or without crooked toes.
- Certain diseases: avian encephalomyelitis or Marek's disease
- Diet: Nutritional deficient diet, especially one that lacks sufficient antioxidants and omega 3 fatty acids.
- Environment: Exposure to continuous lighting or ammonia.