It is due to an excess of eyelid tissue, or a small eye, or both, the result being that a varying amount of hair-covered eyelid can turn in to rub directly against the cornea or conjunctiva, or both. It is usually extremely painful, and the damage caused to the cornea can render the eye blind. Occasionally the condition is self-correcting as the puppy grows, but in the vast majority of affect dogs surgery is necessary to turn the eyelid away from the surface of the eye. Usually such surgery is successful, but it is much better that, as with the other inherited eyelid defects, breeders try to avoid producing this condition in their stock. Exposure of the delicate mucous membrane causes conjunctivitis.
Correction is possible by complicated surgery in which the eyelid is lifted and shortened.
Occasionally further surgery may be necessary to change completely the shape of the eyelids. Cataract is a common secondary feature of the disease. In central PRA night blindness is not a feature and though vision is several affected, the dog may not become totally blind. In both groups of PRA there is degeneration of the photoreceptors, but in the generalized form this degeneration is the inherited defect, whereas in central PRA rod and cone degeneration follows an inherited defect elsewhere in the retina. An inherited condition, a cataract is an opacity of the lens or its capsule.