Ординатура / Офтальмология / Английские материалы / Small Animal Ophthalmology Secrets_Riis_2002
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Figure 18. Cat with retinal and optic disc degeneration. Generalized hyperreflective tapetum and a darker than normal optic disc. The retinal vessels are just about absent.
somal dominant. Mixed breed domestic shorthair cats with a rod-cone dysplasia with possible autosomal dominance are also reported. These retinal lesions are diagnostic ophthalmoscopically at an early age.
21. What is known about retinal atrophy as an inherited disease?
The Abyssinian cats have an autosomal recessive rod-cone degeneration that is progressive. Mixed breed domestic shorthair cats with gyrate atrophy have been diagnosed to have an ornithine aminotransferase deficiency that is inherited as autosomal recessive.
22.What are the infectious causes of retinal lesions in cats?
Kittens infected with panleukopenia virus 7 days before birth through 7 days postbirth are
known to develop retinal dysplasia or cerebellar hypoplasia. Those kittens are neurologically ataxic and hypermetric. They are usually presented for these signs between the ages of 3 and 4 weeks of age. Funduscopic lesions are not always present but are pathognomonic when found (Fig. 19).
Figure 19. Young kitten with retinal degenerative areas throughout secondary to panleukopenia virus infection.
23.What are the nutritional causes of retinal atrophy in cats?
Any cat breed is likely to develop a degenerative retinopathy if its diet is deficient in tau-
rine. The early stages are classical as the degeneration is zonal within the area centralis progressing horizontally from the central retina toward the periphery. Advanced degenerations look like any other end-stage retinal atrophy. These lesions are known as feline central retinal degeneration (FCRD). Since taurine was discovered as a required amino acid in cat diets, the pet food industry has dramatically reduced the incidence of this retinopathy by taurine supplementation (Fig. 20).
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Figure 20. Feline central retinal degeneration secondary to nutritional causes (i.e., taurine deficiency). The well-demarcated zones of hyperreflectivity on either side of the optic disc are areas of degeneration (»), At this stage, the cat is still visual.
24. What are some of the causes of retinal toxic degenerations?
Liver disease and gallbladder stones have an ocular manifestation of retinal degeneration. Recently, Baytril, given at the recommended systemic dose, has been reported to cause retinal degeneration in cats (Fig. 21).
Figure 21. Retinal degeneration thought to be secondary to enrofloxacin (Baytril) administration. (To prevent retinal complications, do not exceed 5 mg/kg/day.)
25. Are there blood tests available for cat retinal degeneration?
No. DNA-based tests are not currently available to identify cats that are affected, are carriers, or are genetically normal for PRA or other inherited retinal diseases.
BIBLIOGRAPHY
I. Acland GM, Aguirre G, Chader GJ, et al. Canine early-onset hereditary retinal degeneration: genetic and biochemical distinction of 3 diseases (abstract). Invest Ophthalmol Vis Sci 119:250,1980.
2.Acland GM, Blanton SH, Hershfie1d B, et al: XL-PRA: A canine retinal degeneration inherited as an X- linked trait. Am J Med Genet 52:27-33,1994.
3.Aguirre GD: Inherited retinal degenerations in the dog. Trans Am Acad Ophthalmol Otolaryngol 81:667-676,1976.
4.Aguirre GD: Retinal degenerations in the dog. 1. Rod dysplasia. Exp Eye Res 26:233-253, 1978.
5.Curtis R, Barnett KC: Progressive retinal atrophy in miniature longhaired dachshund dogs. Br Vet J 149:71-85, 1993.
6.Gelatt KN, Van der Woerdt A, Ketring KL, et al: Enrofloxacin-associated retinal degeneration in cats. Vet OphthalmoI4:99-106, 2001.
7.Hakansson N, Narfstrom K: Progressive retinal atrophy in papillon dogs in Sweden. A clinical survey. Vet Comp OphthalmoI5:83-87, 1995.
8.Narfstrorn K, Ehinger B, Brunn A: Immunohistochemical studies of core photoreceptors and cells of the inner retina in feline rod-cone degeneration. Vet OphthalmoI4:141-145, 2001.
9.Parshall C, Wyman M, Nitray S, et al: Photoreceptor dysplasia: An inherited progressive retinal atrophy
in miniature schnauzer dogs. Prog Vet Comp Ophthalmoll: 187-203, 1991.
10. Ray K, Baldwin V, Acland G, et al: Molecular diagnostic tests for ascertainment of genotype at the rodcone dysplasia I (rcdl) locus in Irish setters. Curr Eye Res 14:243-247, 1995.
II. Sandberg MA, Pawlyk BS, Berson EL: Full-field electroretinograms in miniature poodles with progressive rod-cone degeneration. Invest Ophthalmol Sci. 27:1179-1184,1986.
40. RETINAL DYSPLASIA
Ronald C. Riis, D.V.M., M.S.
1.What is the definition of retinal dysplasia (RD)?
RD is an abnormal development of the retina.
2.What causes the abnormal development?
RD lesions in puppies have been caused by adenovirus and herpesvirus infections and in kit-
tens by panleukopenia virus. Some RD lesions are associated with genetic traits such as a simple recessive in Bedlington terriers, golden retrievers, and Labrador retrievers and as recessive in American cocker spaniels, beagles, collies, corgis, English springer spaniels, and Sealyham terriers.
In addition to RD, other ocular lesions have been diagnosed, such as cataracts, colobomas, persistent pupillary membranes, retinal detachments, hemorrhage, and microphthalmia.
The most noted breeds with RD and other anomalies include (* = most common):
Akita* |
American cocker spaniel* |
Australian shepherd* |
Beagle |
Basset griffon Veudeen (petite) |
Bedlington terrier |
Belgian Malinois |
Border collie |
Bull mastiff |
Collie* |
Cavalier King Charles spaniel |
Chow chow |
Clumber spaniel |
Doberman pinscher |
English springer spaniel* |
Field spaniel |
German shepherd |
Golden retriever |
Gordon setter |
Labrador retriever" |
Mastiff |
Norwegian elkhound |
Old English sheepdog |
Pembroke Welsh corgi |
Rottweiler |
Samoyed* |
Sealyham terrier |
Yorkshire terrier |
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3.Has RD been referred to by other names?
RD was once called "vermiform streaks" because ophthalmoscopically the lesions looked
like worms imbedded in the retina. Because the pathology of RD may take on the appearance of retinal rosettes or uplifting folds away from the retinal pigment epithelium, "retinal folds" became a popular term, especially if the dysplasia was linear, with and without branching.
4.Are there degrees of RD?
Yes, the linear dysplastic lesions (folds) are usually the least serious. When the linear lesions
become numerous and fuse together, a larger area of retina is scarred. These areas take on various shapes with some appearing like states or countries on a map, thus the name "geographic RD" (Figs. 1-8).
Figure I. Yellow Labrador puppy with multiple linear retinal folds in the nontapetum and focal scars in the developing tapetum.
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Figure 2. Young American cocker spaniel with retinal folds.
Figure 3. Nontapetal retinal folds. Note venules crossing retinal folds.
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Figure 4. Six-month-old beagle with many nontapetal retinal folds that are fading with pigment from the retinal pigment epithelium.
Figure 5. A 6-week-old Australian shepherd puppy with elongated retinal folds.
Figure 6. A 4-month-old Akita puppy with focal and linear retinal dysplasia.
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Figure 7. A 6-month-old bull mastiff puppy with multifocal retinal dysplasia.
Figure 8. An adult springer spaniel with multiple tapetal scars dorsal to the disc. Pigmentation has proliferated among the hyperreflective areas.
5. Can RD lesions heal
Yes and no. The first answer is yes because the retina will compensate in various ways. The small linear lesions (folds) take on a gray or hyperreflective appearance within the tapetal fundus, whereas the same type of RD lesion may pigment with melanocytes in the nontapetal fundus. These areas never heal to become functional, but do scar to form pathologic thin areas of the retina. Very large geographic RD lesions may also scar, but the larger lesions might be complicated with detachment.
Some of the infectious RD lesions take on punctuate or circular appearances in both the cat and dog. They may become ophthalmoscopically healed or less numerous over the years. Even though the RD may have been severe and only a few scars remain, the owner may comment about some visual impairment.
6. When should the retinas be examined for RD?
Most conscientious breeders present their puppies for evaluation before they are placed in homes. Between 6 and 9 weeks of age which is a good time to rule out RD in the "fold" category.
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However, examination at this age does not guarantee the puppies will be free of all types of RD. Puppies that are free of linear fold RD at 6-9 weeks have later been found to have geographic RD. Therefore, it is recommended to have examinations performed between the ages of 6 and 9 weeks and again at 6-9 months.
7. If an animal is diagnosed with RD, should it be bred?
It depends on the type of RD and breed. The minor linear fold RD lesions are thought to be nonprogressive and not visually impairing. Usually, these lesions are left to the breeder's discretion when rating animals for show and breeding quality.
The larger geographic RD lesions are serious enough that animals with them should not be bred. RD is often associated with infectious or anomalous development and not genetic causes, so these animals could be bred. However, it is difficult to judge etiology in older, scarred retinas, so caution should be taken (Figs. 9-14).
Figure 9. An adult springer spaniel with nontapetal retinal dysplasia and focal detachment.
Figure 10. A springer spaniel puppy with retinal detachment and generalized retinal folds over the entire fundus.
Figure 11. Retinal dysplasia adjacent to the optic disc with associated retinal detachment.
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Figure 12. An adult beagle with multifocal coalescent retinal folds causing retinal detachment dorsal to the optic disc.
Figure 13. A geographic retinal dysplastic lesion in an American cocker spaniel.
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Figure 14. A very large geographic retinal dysplastic lesion.
8.What is the most severe RD presentation?
Blind puppies with retinal detachment secondary to the dysplasia. These puppies usually
have a rotary nystagmus. The leukocoria present is the retina dislocated just behind the lens. Some of these puppies also have microphthalmia or intraocular hemorrhage. Ironically, the severe presentation does not always happen bilaterally.
9.What is the least severe RD presentation?
Those eyes that are entirely normal with the exception of a few small linear or dot retinal
scars.
10.If the minor RD lesions were reevaluated at an older age, couldn't they be potentially normal?
The RD areas may fill in with pigment, especially if they were noted only in the nontapetal fundus. Evaluation records have documented that animals do go from phenotypic affected to phenotypic normal. However, the earlier evaluation determines whether the animal is geneotypically affected, and the inherited traits will be passed on.
11.Is it difficult to examine eyes for RD lesions?
The early examination (6-9 weeks of age) is the most difficult. This age normally requires
good restraint, maximally dilated pupils, expertise with ophthalmoscopic techniques, and persistence for a good view of the fundus periphery.
12. Should all puppies be referred to a diplomate of the American College of Veterinary Ophthalmologists (DACVO) for the early evaluation?
Not necessarily. If a veterinarian feels comfortable evaluating the puppies, referral may not be required unless a lesion is questionable or a second opinion is recommended. If the breeder or owner desires certification by the Canine Eye Registration Foundation (CERF), it is necessary to refer to a DACVO member because CERF only accepts their evaluations.
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13.Is there a DNA test for RD? Not yet.
14.Has RD been classified any other way?
RD has been classified histopathologically by the rosette architecture. Three layer rosettes indicate a mature retina that has detached and in which folds have developed. Two layer rosettes and one layer rosettes arise from either the outer or inner retinal layers. These are examples of true dysgenesis (Figs. 15 and 16).
Figure 15. Histopathology of a retinal fold (formalin fixed). Note photoreceptor and outer nuclear layer fold. 10X.
Figure 16. Histopathology of a large retinal fold (formalin fixed). Note rosette of outer nuclear layer.40X.
CONTROVERSY
15.Should animals with RD fold scars be bred?
For: Many breed organizations have taken a stand on this question. Because RD fold scars
are a minor flaw and all other characteristics about the animal may be highly desirable, it is irrational to cull the animal for this trait alone.