A cataract is a clouding of the lens of the eye causing a deficit or loss of vision. Cataracts in dogs less than 6 months of age are usually congenital (existing at or before birth) or juvenile (developing from birth until 6 years of age) cataracts. Heredity is the major cause in both cases. Visualization of the cataract can be difficult – it presents as a white, cloudy area or spot deep within the black pupil of the eye. Some cataracts progress (become worse), while others remain the same or even resolve. Dogs that develop cataracts should never be used in a breeding program.