Day Blindness also known as Achromatopsia , or color blindness, is characterized by cone photoreceptor dysfunction, causing severely reduced or complete vision loss during daylight hours. Dogs may also show signs of avoiding bright light or distress in bright light (photophobia), and total colour-blindness. The disease is present at birth (i.e. it is congenital) and clinical signs show when dogs are approximately 8-10 weeks of age. Achromatopsia is an autosomal recessive disease characterized by the loss of cone photoreceptor function that results in day-blindness, total colorblindness, and decreased central visual acuity.