Progressive retinal atrophy (PRA) affects about 7% of Tollers with an estimated 40% being carriers. The type of PRA associated with the breed is known as progressive rod-cone degeneration. The disease causes cells in the retina to degenerate and die. This causes night blindness at first and eventually complete blindness. Collie eye anomaly is estimated to have a carrier rate of 5% and an affected rate of 0.5%. It generally only causes mildly impaired vision, although in more severe cases it can lead to retinal hemorrhaging and detachments resulting in blindness.