Retinal Degeneration

Home / Retinal Degeneration

Issues

Retinal Degeneration

 

Degeneration of the retina from any cause inherited or acquired.

Inherited—generalized PRA; a group of progressive retinal diseases; may be subdivided into photoreceptor dysplasias (begin before the retina fully develops, < 12 weeks) and photoreceptor degenerations (begin after the retina matures).

 

PATHOPHYSIOLOGY

  • A number of genetic defects in photoreceptor metabolism have been identified.
  • May be secondary to retinal pigment epithelial or choroidal disease; amino acid metabolic disorders, and storage diseases.
  • Central PRA: genetic defect in vitamin E metabolism, can be acquired with vitamin E deficiency.
  • Also may be idiopathic, secondary to diffuse or focal inflammation and scarring (e.g., chorioretinitis), toxin exposure, nutritional deficiency, or previous retinal detachment.

 

SYSTEMS AFFECTED

Nervous system with lysosome storage diseases

Ophthalmic

 

GENETICS

Dogs

  • PRA—autosomal recessive most breeds (see breed predelection).
  • Neuronal ceroid lipofuscinosis—autosomal recessive in most breeds.
  • Hemeralopia—cone degeneration, autosomal recessive.
  • Inheritance in many breeds not determined.

 

Cats

  • Early onset—mixed breed and Abyssinian retinal dysplasia (rod-cone dysplasia), autosomal dominant. Persians (autosomal recessive). Clinical signs at 4 months; may be blind by 2 years.
  • Late onset—Abyssinian autosomal recessive rod cone degeneration: blind by 4 years of age.

 

INCIDENCE/PREVALENCE

  • Hereditary—prevalence greater in dogs than in cats.
  • Taurine deficiency—uncommon now that cat foods are appropriately supplemented.

 

SIGNALMENT

Species

Dog and cat

 

Breed Predilections

  • Hereditary—Dogs
  • Hereditary—Cats

 

Mean Age and Range

Early PRA and dystrophies—3–4 months–2 years

Late PRA—clinical signs > 4–6 years

Cone degeneration disease—3–4 months

Predominant Sex

PRA—X-linked recessive condition in Siberian huskie and Samoyed, therefore more likely to be present in males.

 

SIGNS

Historical Findings

  • PRA (dog)—a gradually progressing nyctalopia that ultimately affects vision in bright light; may note dilated pupils or brighter tapetal reflex; may appear to be acutely blind (when patient becomes totally blind or is moved to unfamiliar surroundings). Dysplasias will have early onset and may be blind by 2 years. Degenerations are later onset and blind in later life.
  • Hemeralopia or cone degeneration disease—rare. Between 8 and 12 weeks of age puppies show photophobia and trouble navigating in bright light. Progresses to total day blindness. Night vision remains normal.
  • Central PRA (dogs)—rare in the United States; central vision lost; may never become completely blind.

 

Physical Examination Findings

  • If severe—direct and consensual pupillary light reflexes impaired or nearly abolished.
  • Tapetal hyperreflectivity and non-tapetal depigmentation or mottled hyperpigmentation; retinal blood vessel attenuation and optic nerve atrophy.
  • PRA (dogs)—cataracts and vitreous degeneration can occur.
  • SARDS (dogs)—obesity; may note slow or absent pupillary light reflexes. Chromatic PLR testing (melan 100), reduce red PLR with escape, normal blue PLR.
  • Borzoi chorioretinopathy—multifocal chorioretinal lesions (hyperpigmented and hyperreflective).
  • Taurine-deficient retinopathy (cats)—begins as a spot in area centralis; then horizontal band forms superior to the optic nerve; finally, diffuse degeneration and hyperreflectivity.
  • Post-inflammatory retinal scars—focal or multifocal lesions manifest as areas of tapetal hyperreflectivity or altered pigmentation.
  • Skeletal dysplasia may be associated with Samoyed and Labrador retriever, i.e., dwarfism.

 

  • Retinal dysplasia may also be associated with multiple other ocular anomalies in Akita, Doberman pinscher, or any breed.
  • Storage diseases—may have cloudy corneas and possibly neurologic signs.
  • Neuronal ceroid lipofuscinosis—mental deterioration, CNS signs, paralysis, and death.

 

CAUSES

Degenerative

  • PRA—affects both eyes symmetrically; most forms of PRA are recessively inherited except for dominant PRA in mastiffs.
  • Chronic or uncontrolled glaucoma—retinal and optic nerve atrophy.
  • Secondary to scarring from previous multifocal or diffuse retinal detachment or inflammation.

Anomalous

  • Rod-cone dysplasias—affect both eyes.
  • Other dysplasias—may be multifocal and non-blinding (e.g., in English springer spaniel and Labrador retriever).
  • Oculoskeletal dysplasia in Labrador and Samoyed.

 

Metabolic

  • Storage disease—mucopolysaccharidosis, gangliosidosis, mannosidosis, fucosidisis (English spriner spaniel).
  • Ornithine aminotransferase deficiency—progressive and totalatrophy of the choroid and retina, manifests in older cats.
  • Neoplastic
  • Neoplastic cell infiltrate may lead to scars from previous retinal detachment if treated.

 

Nutritional

  • Severe deficiency of vitamin E or A (dogs and cats)—dogs fed poor diets (high in polyunsaturated fats) may cause partial or complete degeneration.
  • Taurine deficiency (cats)—causes retinal degeneration and dilated cardiomyopathy.
  • Infectious/Immune
  • Retina will degenerate from inflammation; may be focal, multifocal, or generalized.

 

Idiopathic

  • SARDS—dogs; post-inflammatory—dogs and cats.

 

Toxic

  • Idiosyncratic reaction to griseofulvin or enrofloxacin (cats).
  • Radiation—dogs or cats treated for nasal or CNS neoplasia.
  • Phototoxicity—operating micrscopes, welding light exposure.

 

RISK FACTORS

  • Ocular disease—cataracts; panuveitis; chorioretinitis; retinal detachment; glaucoma.
  • Cats—enrofloxacin dose should not exceed 5 mg/kg/day. Toxicity noted at lower doses especially in compromised animals, i.e., renal disease.

 

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

  • Acute vision loss—pupillary light reflex slow or absent: SARDS, optic neuritis, retinal detachment, unrecognized PRA, or glaucoma; pupillary light reflex normal: rapidly developing diabetic cataracts or visual cortex disease.
  • Slowly progressive visual loss—PRA; cataracts; severe corneal disease (e.g., pigmentation, scarring, or edema); chronic retinitis; chorioretinitis; vitreal inflammation.

 

CBC/BIOCHEMISTRY/URINALYSIS

  • Usually normal, unless systemic disease.
  • SARDS (dogs)—results may be suggestive of hyperadrenocorticism, which patient may have.

 

OTHER LABORATORY TESTS

  • Test for Cushing’s disease,, evaluate sex hormone levels, check blood pressure, evaluate for proteinuria—with SARDS.
  • Taurine concentration (cats)—especially with dilated cardiomyopathy.
  • Serum and urine ornithine concentrations (cats)—elevated with ornithine aminotransferase deficiency.
  • Genetic testing—OptiGen, VetGen or Michigan State University. New tests for a variety of breeds are steadily being developed. Details on tests available, samples needed, and how to interpret test results may be found at testing center websites. Test results often allow identification of affected, non-affected, and probable carriers with good confidence.

 

IMAGING

  • Thoracic radiographs and cardiac ultrasound—may be indicated in cats with suspected taurine-deficient condition.
  • Abdominal radiographs and ultrasound (dogs)—with SARDS if Cushing’s disease is suspected.
  • CT or MRI—used to rule out causes of central blindness (e.g., optic nerve damage, cortical blindness).

 

DIAGNOSTIC PROCEDURES

  • Ophthalmic examination.
  • Electroretinography-localizes cause of blindness (when retina not visible or appears normal).
  • Chromatic PLR (Melan 100)—can help screen for outer retinal layer problems (red reduced) vs. inner retina layers (absent blue). Definitive diagnosis requires electroretinogram as assessment of PLR is subjective and interpretation can be confounded by iris atrophy and stress-induced mydriasis.
  • CSF tap—may be performed for cases of suspected optic neuritis.

 

PATHOLOGIC FINDINGS

  • Thin retina.
  • Edges of focal retinal scars—sharply delineated.
  • Hyperpigmented areas—associated with post-inflammatory scars or central PRA.
  • End-stage degenerations—marked photoreceptor atrophy and reduction in retinal cell density.
  • Lipopigment accumulated in the neuroepithelium—central PRA, ceroid lipofuscinosis, congenital stationary night blindness.
  • Lysosome storage diseases—accumulation in neuronal/retinal layers/cornea.

TREATMENT

DIET

  • Cats—food should contain 500–750 ppm taurine.
  • Dogs—balanced diet, avoid all meat high in polyunsaturated fats.

 

CLIENT EDUCATION

  • Inform client that most blind animals function well in stable environment.
  • Advise client that blind dogs should be supervised if they are outside, not in fenced yards or in an area with a pool.
  • Suggest playing with toys that make sounds.
  • Some old blind animals with other problems such as hearing loss or senility may not adapt well.
  • Some blind animals experience behavioral changes such as increased aggression or reduced activity.
  • Animals with only one blind eye can function normally.
  • Blind cats should be kept indoors.

 

SURGICAL CONSIDERATIONS

Not indicated unless painful eye.

 

MEDICATIONS

DRUG(S)

  • None currently effective.
  • Pyridoxine supplementation (cats)—for ornithine aminotransferase deficiency.
  • Adequate dietary taurine—may halt the progression of the taurine-deficient retinopathy.

GENE THERAPY

Experimental—RPE dystrophy in the Briard.

 

PRECAUTIONS

Cataract surgery—not recommended if retinal degeneration is severe; perform preoperative electroretinogram.

 

FOLLOW-UP

PATIENT MONITORING

Serial fundic examinations—will note signs of degeneration over weeks with SARDS; months PRA.

Cataract formation—with PRA or SARDS.

 

PREVENTION/AVOIDANCE

  • Do not breed animals suspected of having PRA.
  • Do not breed known carriers (e.g., offspring of affected).
  • Do genetic testing on breeding animals.

 

POSSIBLE COMPLICATIONS

  • Cataracts
  • Glaucoma
  • Uveitis
  • Ocular trauma as a result of visual impairment
  • Obesity—secondary to reduced activity

 

EXPECTED COURSE AND PROGNOSIS

  • Inherited PRA—progresses to blindness; progression often slow enough for patient to adapt to visual loss; non-painful.
  • Degeneration from previous inflammation—usually does not progress unless a systemic disease or autoimmune etiology causes persistent or recurrent inflammation.
  • SARDS—irreversible blindness.
  • Transient taurine deficiency (cats)—degeneration may halt at any stage.

MISCELLANEOUS

ASSOCIATED CONDITIONS

SARDS—hyperadrenocorticism, proteinuria, hypertension, elevated sex hormones

 

ABBREVIATIONS

CNS = central nervous system

CSF = cerebrospinal fluid

CT = computed tomography

MRI = magnetic resonance imaging

PLR = pupillary light reflex

PRA = progressive retinal atrophy

RPE = retinal pigment epithelium

SARDS = sudden acquired retinal degeneration syndrome

 

Visit your veterinarian as early recognition, diagnosis, and treatment are essential.

You may also visit: https://www.facebook.com/angkopparasahayop