Achromatopsia, also called rod monochromacy, is an inherited condition characterized by decreased visual acuity, absent color vision, photophobia, and nystagmus. Achromatopsic humans report that colored objects appear in shades of gray. Two forms of this condition have been described in humans. Complete achromatopsia is a congenital vision disorder in which all cone function is absent or severely diminished. The incomplete (atypical) form is defined as dyschromatopsia, in which the symptoms are similar to those of the complete achromatopsia (typical) form but with less visual dysfunction3. In dogs, the condition is referred to as canine cone degeneration. Cones are light-sensitive retinal photoreceptors in the vertebrate eye. Although cone cells account for only 5% of photoreceptors, they are essential for high-acuity daylight-vision and discrimination of color.
Canine cone degeneration is caused by mutation in the canine GNGB3 gene. In the Alaskan Malamute, the complete gene is deleted, while in the German Shorthaired Pointer, the gene has substituted amino acids4. The disorder has also been described in the Miniature Poodle and other breeds of dogs. Affected dogs do not lose eyesight and remain normal throughout life.2 Puppies develop day-blindness and photophobia between 8 and 12 weeks. You will know that a dog has day-blindness when you notice him colliding with obstacles in daylight. Symptoms are present only in bright light, while vision in dim light is normal.
Achromatopsia has been reported in Australian shepherds
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- Joseph Besharse, Dean Bok. The Retina and Its Disorders
- Evaluation of a behavioral method for objective vision testing and identification of achromatopsia in dogs
- Photoreceptor Structure and Function in Patients with Congenital Achromatopsia
- Elias I. Traboulsi. Genetic Diseases of the Eye