ETIOLOGYRetinal folds and retinal dysplasia are closely related eye diseases that are primarily inherited, suspected to be autosomal recessive. Other causes include toxicity and infections during pregnancy, including herpesvirus and possibly parvovirus. These diseases are found in bichons, although not frequent among our breed compared to some other breeds. CERF reports for the last 12 years cite 43 cases in bichons, but this does not account for the majority of bichons who do not undergo annual CERF examination. Because these diseases may cause blindness in puppies, bichon breeders need to be aware that we should not be breeding affected bichons, and of course we should all CERF our breeding stock.
PATHOPHYSIOLOGYThe retina is a layer of sensory tissue that is attached to the tissue in the back of the eye. The retina receives light stimuli from the environment and converts it to an electric signal that is sent to the brain via the optic nerve, which lies behind the retina. The brain interprets this signal and vision occurs. Any alterations in the retinal tissue can impair vision. The retinal tissue undergoes changes until the eye is fully developed at the age of one year.
Dysplasia is defined as abnormal growth or development. Retinal dysplasia forms when the 2 developmental layers of the retina do not unite properly. It can involve both eyes or one, but the inherited form is almost always bilateral. It can occur anytime during eye development, from pregnancy to one year of age. There are 3 forms of retinal dysplasia:
Focal retinal folds: These are wrinkles in the retinal tissue in one or more areas. They cause small blind spots, but rarely cause visual impairment for the dog. They primarily occur in young dogs with developing retinas, and usually disappear by the age of one year. Young dogs (<1 year of age) with folds only are not at risk of developing dysplasia at a later age.
Geographic retinal dysplasia: This consists of irregularly shaped areas of the retinal tissue that appear like a rosette upon examination. This may cause some degree of visual impairment and possibly blindness. This can develop at anytime up to one year of age and is usually permanent. In puppies, this can co-exist with folds since folds and dysplasia are difficult to differentiate in the immature retina. As the folds disappear later when the retinas mature, the dysplasia will persist.
Generalized or complete retinal dysplasia: This form exhibits severe retinal disorganization and is associated with detachment of the retina. Detachment occurs when the retinal sensory tissue separates from the tissue in the back of the eye, thereby causing complete blindness. This is detectable at birth and is permanent.
PROGRESSIONRetinal dysplasia is not a progressive disease, but it will continue to develop until the retinas are mature at around one year of age. To allow the retinas time to mature, the earliest age for a CERF screening for this disease is 6 months, yet closer to one year is recommended by Dr. Kirk Gelatt at which time a definite diagnosis can be established. If you suspect one of your puppies has visual impairment, seek an ophthalmology exam immediately. Signs would include frequently bumping into objects, less activity, and possibly timid or fearful.
MANAGEMENTThere is no treatment for this disease. The best we can do is to strive to prevent it. The literature recommends that dogs affected with either of the 2 more serious forms of dysplasia (geographic or complete) should not be bred, as well as their parents and their littermates. The genetic relationship between retinal folds and the other 2 forms of dysplasia is unknown at this time. Some ophthalmologists suggest that a mature dog with persistent retinal folds may produce more severe forms of the disease in their offspring, secondary to the dog being a carrier of the gene for the more severe forms of dysplasia. What appear to be folds on exam can sometimes be dysplasia, so a mature dog with folds or dysplasia should not pass a CERF exam. In addition, one may wonder if retinal dysplasia could play a role in the incidence of retinal detachments that occur after bichon cataract surgery. According to Dr. Kirk Gelatt, post-operative detachments are primarily related to “cataract maturity and the secondary lens-induced inflammation, rather than retinal dysplasia”.
ADVICE FOR BREEDERSAs responsible bichon frise breeders, we need to be aware of retinal dysplasia and stop the progression of this disease in our breed while the incidence is low. We can accomplish this by completing the initial CERF exam near the age of one year and not breeding bichons with persistent retinal folds or retinal dysplasia. In the past, some bichon breeders were advised that there is no reason to CERF until the age of 2 years, since the age of onset of the bichon cataract is 1.5-2years. Dr. Gelatt feels that although this disease is limited in bichons and seldom impairs vision, an affected bichon and its parents should not be used for breeding. He also states “There is no reason to CERF before six months to one year unless you suspect vision problems.” Besides, knowing that your bichon has retinal dysplasia would be beneficial before spending the time and money to complete its championship.
Since the Health and Education Committee feels that this disease deserves vigilance, we will keep you informed on recommendations for screening for retinal folds and dysplasia. We also encourage you to share data with our committee, which will remain confidential, so that we can be aware of current trends in health problems in bichons.
Research for this article includes The Merck Veterinary Manual,
The Dog Owners Veterinary Handbook
plus numerous medical and veterinary sources
Article reviewed for accuracy by Kirk Gelatt, VMD
Professor of Veterinary Ophthalmology
College of Veterinary Medicine
University of Florida
http://www.bichonhealth.org/
