Eye Problems in Retrievers
by Dennis K. Olivero, DVM
Retinal folds are caused by multiple factors and they have a variable clinical significance. The significance largely depends on the breed in which they occur. We will soon be offering a DNA test for a condition called OculoSkeletal Dysplasia (OSD) that occurs in Labrador Retrievers and Siberian Huskies. This condition can cause retinal folds as well as more severe disease (blindness and dwarfism). One of the other DNA tests we offer (CMR) can also be useful in preventing retinal folds.
Retinal dysplasia is the most important retinal disease affecting Labrador Retrievers used for hunting or field trial work. The condition is relatively uncommon in lines of Labradors used for conformation work. Dysplasia is a term which is used by scientists who study development and refers to an abnormal development of any organ in the body, such as the bones of the skeleton (skeletal dysplasia), or the nervous layer of the eye (retinal dysplasia). Retinal dysplasia, in a clinical sense, refers to a group of ocular abnormalities which are genetically programmed in Labrador Retrievers.
Retinal dysplasia involved abnormal development of several structures of the visual system. Dogs may be very mildly affected and demonstrate folds in the retina. These are areas where extra retina develops and instead of forming a thin membrane over the back surface of the eye, the extra retina develops into folds. Because the retina folds over upon itself, light cannot be focused in this area of the retina. This results in a blind spot. Oftentimes, the involved retina is also under nourished and an area of retinal degeneration (death of the nervous cells) will occur. Dogs with mild changes associated with retinal dysplasia (for example, a few retinal folds) usually have no visual compromise which can be detected by the ophthalmologists or the trainer. Behavioral modification on the part of the dog, such as subtle changes in the positioning of the head while marking a bird, helps affected Labradors to make use of normal areas of the retina. Larger blind spots may cause dogs to miss a mark or miss stationary objects, while these dogs appear to be able to perceive moving objects with less difficulty.
Labrador Retrievers with more severe forms of retinal dysplasia may have more severe visual compromise or blindness. This results from several changes including large areas of retinal folds or degeneration. Retinal separation or detachment can also develop in these dogs resulting in complete loss of vision from the involved eyes. Cataracts are noted in association with the more severe forms of retinal dysplasia in Labradors. Lastly, the severe form also may involve the development of eyes which are larger than normal. This results in the lens focusing the light in front of the retina (near sightedness), because enlargement of the eye places the retina further behind the lens than normal. These dogs have a "bug eyed" appearance and see poorly even in the absence of severe retinal changes or cataracts.
There is no question that retinal dysplasia is an inherited condition on [sic] Labradors. The condition is widespread in this country. During CERF clinics in Minnesota the disease is noted in 10-20% of dogs examined. Most dogs have a mild form of the disease and their trainers have not noticed a visual problem. Once diagnosed, however, some trainers do remark on a dog's problem with finding down birds or marking in one particular direction. Although other retriever and pointing dogs have inherited eye problems distinct to their breeds none of them appear to have the retinal dysplasia syndrome as recognized in the Labrador.
Retinal dysplasia in Labradors has been shown recently to be the result of a dominant gene. Dogs with only a single dose of the genetic information for this condition (from either stud or bitch, but not both) usually develop the very mild forms of the conditions, with retinal folds. These folds usually can be seen early in life and the optimal time, (for the ophthalmologist) to evaluate these dogs is about 8-16 weeks of age. In theory, retinal folds can be noted at this time and the affected puppy, then not used in future breeding programs. Most of these dogs are so mildly affected and suffer no known visual compromise they are excellent for hunting dogs or for pets. Some trainers, however, may not wish to invest the time and money into a dog for field trial work if they have genetic information for retinal dysplasia. Because the retina continues to develop until about 6 months of age and because puppies are admittedly difficult to evaluate critically, some subtle retinal changes can be missed at 8 - 12 weeks of age. A very thorough exam, however, is possible in the 6 month (or older) dog.
More severe forms of retinal dysplasia with retinal separation, cataract, and eye enlargement develop in dogs which inherit a gene from both the bitch and the stud dog. These dogs also may suffer from skeletal dysplasia or dwarfism, as the same gene for retinal dysplasia (which works in a dominant fashion for the eyes) causes skeletal dysplasia (in a recessive fashion). These dogs are usually obvious to the breeder and the trainer of Labradors and are not often evaluated by ophthalmologists.
Because retinal dysplasia is a dominant trait for the eyes, it should be one which, with a concerted effort on the part of dog enthusiasts, could be removed from the breed by careful selection of dogs for breeding which do not come from lines with the condition and by using dogs who were examined at an early age and found to be clear. Examining the two year old dog prior to breeding is not as sure a means to prevent the introduction of this condition into your line of dogs because very small retinal folds noted at an early age can "straighten out" with growth, making the condition clinically impossible to diagnose in the older dog, although the dog has genetic information to produce other dogs with mild to severe forms of dysplasia. Examining the older dog, after months to years of expensive training and effort, can also produce disappointment to the trainer when it is found that retinal folds or mild cataracts are present.
Dennis K. Olivero, DVM
Diplomat American College of Veterinary Ophthalmologists
(Reprinted in part from the April 1998 issue of the Retriever Field Trial News)