Day Blindness: History and Update

By: Julie Edwards

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What is day blindness?

Degeneration of the “cones” in the retina of the eye as a result of a mutation of gene CNGB3 causes Cone Degeneration Disease (CD) or hemeralopia or day blindness. Cones enable an animal’s ability to see in bright light.

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Anatomy of a canine Eye

What are the signs and symptoms?

Once retinal development is completed, usually around 7 weeks of age, signs will first appear. Affected pups become almost blind in daylight and afraid of light because exposure to bright light appears irritating and possibly even painful, and as a result will shy away from brightly-lit areas. Affected puppies may bump into objects that unaffected puppies easily avoid. Other signs and symptoms include reluctance to come out of shadows and dark dog houses during the daytime, aggressiveness and fearfulness in unfamiliar settings. As dog gets older, symptoms will not increase and vision in the dark remains normal. How long has it affected the breed? Day blindness was discovered in the early to mid-1960s. Earlier anecdotal references to “night dogs” in the north exist, which are suspected cases of Cone Degeneration Disease. Dr. Kenneth Bourns, of Boru Kennels, first discovered CD in his kennel in 1960 when 3 out of 10 pups in a litter exhibited difficulty trouble seeing during the daytime but not at night. When he came forward, many people suggested he spay and neuter the sire and dam and the entire litter and move on. But, he wanted answers. He and Dr. Lord, at the Ontario Veterinary College, conducted test breedings and they identified the condition as an autosomal recessive disease, which means both parents must at least carry the gene to produce affected offspring (see chart below).

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Although relatively rare, cases still appear from time to time, indicating the gene continues in the current population, and why we have to remain vigilant.

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Can you test for it? A Veterinary Ophthalmologist that is experienced with CD can perform an ERG’s (ElectroRetinoGrams) to look for the distinct characteristic cone to confirm a suspected case of day blindness. This may require the dog to go under general anesthesia or light sedation to keep the dog still during the exam. OptiGen Labs in New Yorknow offers a DNA test for CD. Developed by Dr. Acland and Dr. Aguirre, this proved a breakthrough for Alaskan Malamutes and German Shorthaired Pointers (also affected by the disorder). It can determine non-carrier, carrier, or affected DNA status of tested animals.   OptiGen offers the test for the regular price of $160.  They also hold discount periods once a year and a 25% discount for 20/20 clinics, if through a scheduled event and if 20 or more samples are submitted at one time. Please contact OptiGen to schedule an event to take advantage of this discount. OptiGen also extends Free DNA testing for any CD affected pedigreed dogs that have been diagnosed by a veterinary ophthalmologist.

 

How should the DNA test be used? Due to the relative rarity of the disorder, most pedigrees should be tested, and especially those with known or suspected relatives with day blindness. If an animal is found to be a carrier, it can be bred to a confirmed non-carrier, and then testing the offspring. This will help keep the pool more diverse by not excluding as many animals.

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Is treatment available? In the beginning, some people actually tried sunglasses, with mixed results. But, obviously having any malamute wear sunglasses may not make for a realistic solution; although the dogs pictured below seem to realize how cool they look (these dogs do NOT have day blindness, they’re just “cool.”). Tinted contact lenses may also be an option. Currently, Dr. Andras Komaromy at the University of Pennsylvania is conducting successful pre-clinical trials of gene therapy.  The lab administers a correct copy of the CNGB3 gene directly into the retina of CD affected dogs and so far, treated dogs show signs of improvement.  If the success of the trials continues, the treatment should soon be available to the public. Another victory in the ongoing quest for the health of the Alaskan Malamute, this DNA test roved very promising for future DNA tests.  If your Alaskan Malamute may be at risk of being a carrier for Cone Degeneration, please consider testing your dog. Sources:

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1. OptiGen website- http://www.optigen.com/opt9_test_cd.html

2. Minnesota Malamute Club website- https://www.minnesotamalamuteclub.com/

3. Malamute Health website- http://www.malamutehealth.org/articles/eye_dayblindness.htm

4. Correspondence with OptiGen Labs