Disorders of the lens are a common canine eye problem. The most frequent lens problem is cataracts. A cataract is defined as any opacity of the crystalline lens or its capsules. The opacity can be very small, smaller than a pin head, or it can cover the entire lens resulting in blindness. Cataracts can be acquired or inherited, being caused by many factors including trauma, poor diet, inherited defects in the eye, diabetes and degeneration, and the exact cause of a cataract observed in any individual dog is often difficult to determine.
Posterior Polar Subcapsular Cataract
This is by far the most common form of cataract in the Labrador and is a small (often triangular) area at the back of the lens. It is usually static, has no significant effect on vision and in most cases does not worsen, however, in a small percentage of dogs diagnosed with this condition (less than 5%) it can progress. It is detected by an eye test and can be seen in youngsters from about 12 months of age, although it is more often seen when they are a bit older. It is known to be genetic and believed to be inherited through an autosomal dominant gene, i.e. the progeny of a dog with post polar opacities has a 50/50 chance of inheriting the condition from its affected parent. It is therefore inadvisable to breed from a dog with this form of cataract.
Anterior Subcapsular and Peripheral Cortical Cataracts
These forms of cataract are often detected in much older dogs who can be 7 years of age or more before they are detected. These cataracts do not usually lead to blindness, although there will be some loss of sight. Again dogs displaying these conditions should not be bred from. In many cases cataracts can be surgically removed, restoring sight.
General Progressive Retinal Atrophy (GPRA)
In this condition the entire lens degenerates and it can lead to total blindness. There is no cure for PRA. There are basically two types, firstly, early onset PRA which can occur in puppies as young as 6 weeks. Often the first sign that something is wrong will be failing sight at night (night blindness) which can progress to total blindness within 1-2 years. Late onset PRA (progressive rod-cone degeneration) is where peripheral vision is lost first. In this case dogs can be as old as 6 years before it is detected, and this can cause problems as dogs and bitches may have produced several litters before PRA was detected. There is now a new test that can detect PRA in dogs by looking at their DNA. It is expensive and not 100% accurate, however, young dogs can be tested to see if they are clear (do not possess the gene), affected (have the gene and will go on to develop PRA) or are carriers (have a recessive form of the gene though will never develop the condition). Obviously affected dogs should never be bred from, although a carrier dog if mated to a clear dog will not produce any affected puppies.