Eye Anomalies in Australian Shepherds

 

PRA / PRCD

 

Progressive Retinal Atrophy is a group of genetic diseases that that cause the retina of the eye to degenerate slowly over time. Prcd (progressive rod-cone degeneration) is one form of this disease. Prcd-PRA is a recessive inherited trait—like blue eyes in humans. The offspring can only become affected by the disease if they are passed two recessive genes—one from each parent. The genetic disorder, prcd-PRA , causes cells in the retina at the back of the eye to degenerate and die, even though the cells seem to  develop normally early in life. The “rod” cells operate in low light levels and are the first to lose normal function. Night blindness results. Then the “cone” cells gradually lose their normal function in full light situations. Most affected dogs will eventually be blind.  It’s important to remember that not all retinal disease is PRA and not all PRA is the prcd form of PRA.

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HC ~ Hereditary Cataracts

 

Hereditary Cataracts are a clouding of the lens of the eye caused by a breakdown of tissue in the eye.  This condition generally results in an inability to see clearly and can cause total blindness. A mutation in the HSF4 gene causes this type of cataracts in several breeds of dogs. In this case, the dog is typically affected bilaterally, in that both eyes are affected by the cataracts.  They usually start by being small and grow progressively, though the speed of growth is highly variable. Some cataracts will grow so slowly that the dog's vision remains relatively clear, while others will grow such a way that the dog will quickly go blind. Corrective surgery is possible, though it is costly and is not always effective.  It should also be noted that not all cataracts are hereditary. Cataracts can also be caused by old age or injury. Also, cataracts that occur in different regions of the lens can also be familial, however, are not attributed to this gene mutation.  

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CD ~ CONE DEGENERATION

 

Cone Degeneration disease causes day-blindness caused by a lack of cone function in the retina of the eye.
CD disease causes degeneration of the retinal "cones" that respond primarily to bright daylight, resulting in what is referred to as "day blindness."  Symptoms of CD are present only in bright light and the dog's vision is not affected in dim light.  Cone Degeneration is inherited as a recessive disorder, so carrier dogs typically do not show any symptoms of the disease. These dogs can still pass on a copy of the mutation to any offspring, and any dog that inherits one copy of the mutation from each parent will be affected by cone degeneration.

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CEA / CH ~ COLLIE EYE ANOMALY

 

Collies share Collie Eye Anomaly (CEA) with several other breeds – it’s not just a problem for collies. CEA is more technically known as Choroidal Hypoplasia (CH). It is a recessively inherited eye disorder that causes abnormal development of the choroid - an important layer of tissue under the retina of the eye.  Based on research done jointly by scientists at Cornell University and at The Fred Hutchinson Cancer Research Center, BOTH the mild and severe forms of CEA/CH disease now are proven to result from the exact same gene and mutation in ALL of the affected breeds.  The mutation acts like a RECESSIVE mutation. That means, both parents of an affected dog must have at least one copy of the mutation and both parents must have passed a copy of the mutation to the offspring. A dog with one mutant copy and one normal copy of the CEA/CH gene is a carrier  while a dog with two copies of the mutation are affected. 

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