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What Do They See & How Do We Know?

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What Do They See & How Do We Know? What Do They See & Cataract4-6 A cataract is any clouding of the normal transparent lens in the eye. Although cataracts can be caused by trauma, How Do We infectious diseases, or nutritional deficiencies, the vast majority of cataracts are inherited and ultimately affect both Know? eyes. Any breed, including mixed breeds can be affected. Some cataracts remain small and may not significantly affect Vision Abnormalities vision. This is true for one particular type of juvenile cataract seen in the Labrador, By Cynthia Cook, DVM, PhD, Dip. ACVO Golden Retrievers and the Belgian Photos by author Tervuren and Shepherd6. However, for a performance dog, even minimal degradation of vision (see Figure 3) may be enough to affect performance. Cataracts are usually progressive, Last month I described what dogs Lens Luxation1-3 ultimately resulting in significant vision normally see. So, what kind of eye impairment (see Figure 4). In these problems do dogs have and how do you This genetic condition is caused by a cases, cataract surgery with implantation know if your dog’s behavior is a result of weakness in the small zonule fibers of a replacement lens can often restore a vision problem? (see Figure 1) that support the lens. All normal vision. I know of many dogs that Dogs have many of the same eye terrier breeds are highly predisposed. have gone on to successfully compete in conditions that people have.The difference As the fibers themselves are not visible agility after cataract surgery. is that our dogs can’t tell us when their on a clinical examination, lens instability vision has changed and, unless there are (lenticulodonesis) is the symptom other eye symptoms, we may not think indicating impending luxation. The lens of vision as a reason for a change in their may remain unstable but not fully luxated behavior. Many of the eye conditions seen (subluxation) for years. Medication may most commonly in dogs are inherited and be used to make the pupil small (miosis) occur with a higher incidence in some and prevent the lens from luxating breeds of dogs. Many breeds commonly forward into the anterior chamber. working in agility have a higher incidence Anterior lens luxation is nearly always of inherited eye disease (see Table 1). associated with acute glaucoma and If your dog is one of these genetically predisposed breeds, annual eye exams treatment involves surgical removal of are indicated. Eye abnormalities may be the lens. A replacement lens may or may present at birth (congenital) or may not not be implanted. Without a replacement occur until 8-10 years of age. Note that lens, vision is blurry and probably not Figure 3: Simulation of vision in an eye with a small, central cataract. congenital abnormalities may or may not adequate for performance work (see be inherited. Figure 2). Figure 2: Simulation of vision in an eye once the lens has been removed Figure 1: Normal ocular anatomy Figure 4: Simulation of vision through a more diffuse cataract. Vision through and not replaced. Near vision is affected more than distance vision. a mature cataract is like looking through a pane of glass painted white. February 09 | Clean Run 47 Glaucoma7 Glaucoma is a condition associated with elevated pressure within the eye. Inside the Although glaucoma is inherited and, often eye, fluid (aqueous humor) is produced by the ciliary body. It circulates around the lens ultimately bilateral, when the first eye is and through the pupil into the anterior chamber, where it exits into the bloodstream affected, behavior may not be noticeably through a meshwork of tissue located in the iridocorneal angle (see Figure 1). Reduced changed. Dogs can accommodate to capacity of the aqueous outflow pathways is the cause of glaucoma. The iridocorneal having vision in only one eye and, although angle can be directly visualized by looking through a special contact lens applied to the their depth perception is reduced, it may eye (gonioscopy). Normal intraocular pressure is in the range of 10-25 mmHg and is be difficult to detect behaviorally. Other measured by a tonometer, a small pen-like object applied to the eye. Both gonioscopy signs of glaucoma include: cloudiness, and tonometry can be performed as part of an examination by an ophthalmologist, redness of the white of the eye, and a without the need for sedation in nearly all cases. dilated pupil. Discomfort is variable. In the Elevated intraocular pressure can rapidly and irreversibly damage the retina. Pressure acute stage, squinting and obvious signs elevation greater than 40 mmHg for 24-48 hours is often associated with blindness. of pain may be seen. As the condition becomes chronic, affected dogs may behave in a more subdued manner; Condition Age of Onset Static or Progressive Prognosis for Vision Breeds Aected* Diagnosis people with glaucoma describe a Lens luxation 1-7 years Usually progressive Guarded to poor Terriers, especially Jack Russell Terriers Examination by headache-like discomfort. Border Collie1 opthalmologist Cataract 0-10 years Usually progressive Good with surgery American Eskimo Examination by Treatment for glaucoma may involve Australian Cattle Dog opthalmologist orally administered medication and Australian Shepherd Bearded Collie topical eye drops, or in some cases, laser Bedlington Terrier Belgian Tervuren surgery. The condition is nearly always Bichon Frise4 Border Collie progressive and becomes more difficult Cavalier King Charles Spaniel to control while still preserving vision. Cocker Spaniels, American and English Collie Even after vision is lost, the elevated Dalmatian Golden Retriever pressure causes discomfort; it is possible to Jack Russell Terrier Labrador Retriever restore comfort using several different Miniature Schnauzer28 surgical procedures. Nova Scotia Duck Tolling Retriever Papillon Poodle Portuguese Water Dog Shetland Sheepdog, Terriers, Welsh Corgi, Cardigan and Pembroke Retinal Dysplasia and Glaucoma Usually Progressive Guarded to poor Australian Cattle Dog Examination by 8-11 5-7 years Beagle29 opthalmologist, Choroidal Hypoplasia Bichon Frise genetic test Boston Terrier These two conditions are present at Cocker Spaniel, American and English Dalmatian birth, completely static, and in most cases Jack Russell Terrier cause minimal impairment of vision. Poodle Choroidal hypoplasia is commonly referred Retinal dysplasia Congenital Static, detectable Mild forms: good English Springer Spaniel30 Examination by at birth Severe forms Cocker Spaniel, American opthalmologist, to as Collie Eye Anomaly although it associated with Golden Retriever8 genetic test is seen in Shelties and Border Collies in 31, 32 retinal detachment: Labrador Retriever 11- 13 poor Samoyed addition to rough and smooth Collies. Because these conditions are detectable Choroidal Congenital Static, detectable Most common Australian Shepherd16 Examination by hypoplasia/ at birth forms are mild: Border Collie33 opthalmologist, in very young puppies, it is possible to “Collie eye anomaly” good Collie11,13,34,37 tonometry, Nova Scotia Duck Tolling Retriever gonioscopy be certain your new performance dog Shetland Sheepdog9 is unaffected. Diagnosis is important Retinal degeneration American Eskimo Examination by to prevent affected or carrier animals Australian Cattle Dog opthalmologist, Australian Shepherd genetic test, from being bred. A more severe form of Border Collie electroretinography retinal dysplasia associated with skeletal Cocker Spaniel, American and English Collie abnormalities is seen in the Labrador English Springer Spaniel Golden Retriever Retriever and Samoyed. The English Labrador Retriever Springer Spaniel also has a form of retinal Poodle Portuguese Water Dogs dysplasia that covers a spectrum from Nova Scotia Duck Tolling Retriever mild retinal folds to retinal detachment Welsh Corgis, Cardigan and Pembroke and blindness. Another congenital Refractive error Static, detectable Correctable All Breeds Retinoscopy Myopia by one year of age malformation, Merle Ocular Dysgenesis, Hyperopia affects all of the pigmented structures in the Anisometropia eye in Australian Shepherds homozygous 14-16 Table 1: *This list is not complete. I have listed those breeds commonly represented in agility competition. A more complete for the merle coat color. This condition is listing of affected breeds can be obtained from The Canine Eye Registration Foundation (www.vmdb.org/cerf.html). CERF also associated with a variety of malformations maintains a registry for individual dogs found to be free of known inherited eye conditions. Optigen (www.optigen.com) has genetic tests for eye conditions (PRA/prcd, retinal dysplasia, choroidal hypoplasia) in some breeds. and can result in severe impairment. 48 Clean Run | February 09 Get Started With Our 4-Jump Kit includes all necessary pipe, fittings and jump cups to build 4 jumps that adjust from 3" to 35" in height Figure 5: Left shows normal dog vision. Right is simulation of vision in a dog with early PRA. Ultimately, affected dogs are completely blind. Retinal Degeneration17-21 an evaluation easily performed by many veterinary ophthalmologists. While There are many forms of retinal All the PVC abnormalities in refraction probably do degeneration; collectively they are not affect the behavior of the companion often referred to as Progressive Retinal dog, they may be a significant factor in Atrophy (PRA). The most common form is You Need the function of the performance dog. Dogs progressive rod-cone degeneration (prcd). with myopia have blurred distance vision This condition affects many breeds and (see Figure 6); those with hyperopia have is caused by an inherited degeneration to Build It blurred near vision (see Figure 7) and those of the retinal photoreceptors (rods and with a different refractive error in each cones). As the dog retina consists of eye (anisometropia) have altered depth primarily rods, a loss of dim light vision Yourself perception. These refractive errors can be is often the first symptom noted (see corrected using contact lenses. However, it Figure 5). The condition is painless and is important to recognize that vision is only usually slowly progressive; companion one of the many reasons our dogs behave dogs adjust to this handicap extremely well.
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