Page 1759 - Cote clinical veterinary advisor dogs and cats 4th

884 Retinal Degeneration

○ Fluoroquinolone-induced retinal degenera- Etiology and Pathophysiology Advanced or Confirmatory Testing
tion in cats (e.g., enrofloxacin, typically • Inherited: breed-specific genetic abnormality • Electroretinogram
VetBooks.ir feline-specific amino acid changes in ○ PRA: always bilateral; variable rate of signs and suspected causes
• Other diagnostics commensurate with clinical
at high dosages [>5 mg/kg/day]) due to
in photoreceptor metabolism (PRA gene)
progression; leads to blindness when both
ABCG2 causing its dysfunction at the
blood-retinal barrier
Early onset: photoreceptors fail to
○ Griseofulvin in cats rods and cones affected TREATMENT
■
○ Ivermectin in dogs and cats develop normally (i.e., dysplasia) Treatment Overview
• Metabolic (e.g., mucopolysaccharidosis, dogs ■ Late onset: photoreceptors develop No treatment exists to regenerate the retina,
and cats) normally but degenerate and the presentation of these patients for
• Typically, rods affected first, causing vision loss often means the disease process
ASSOCIATED DISORDERS nyctalopia has affected the retina extensively. Treatment
• Cataracts • Eventually, cones also affected, resulting in of retinal degeneration consists of controlling
• Retinal detachment hemeralopia and blindness or reversing an underlying cause when one can
• Systemic diseases causing uveitis ○ RPED is a genetic abnormality affecting be identified.
• Hyperadrenocorticism-like signs (p. 485), the retinal pigment epithelium, with Acute General Treatment
regarding SARDS secondary effects on the neural retina
• Taurine deficiency in cats (p. 960) (nine inner retinal layers); rare. • Treat underlying cause (e.g., glaucoma,
○ Multifocal retinopathy manifests in uveitis) when possible to prevent progression
Clinical Presentation affected puppies at 3-4 months of age as of acquired retinal degeneration.
DISEASE FORMS/SUBTYPES multifocal serous retinal detachments. • Investigational treatments include gene
• Bilateral or unilateral • Acquired therapy and retinal allograft transplantation.
○ SARDS is idiopathic, always bilateral, dogs
• Inherited versus acquired only Possible Complications
• Acute onset versus progressive Sudden blindness within days or 1-2 • Cataracts
• Focal, multifocal (chorioretinal scars), ■ weeks • Corneal/scleral trauma due to vision
generalized
■ Normal fundic exam acutely; when impairment
disease is chronic, generalized retinal
HISTORY, CHIEF COMPLAINT degeneration is indistinguishable from Recommended Monitoring
Varies, depending on underlying cause; owner PRA • Varies, depending on underlying cause
may report any or all of the following: • Secondary • Monitor for secondary cataracts and lens-
• Acute or progressive vision impairment or ○ Occurring after resolution of posterior induced uveitis.
blindness uveitis: distemper, systemic mycoses, • If SARDS is suspected but cannot be con-
• Red eye and/or other signs of glaucoma or toxoplasmosis, hypertension, hemorrhage, firmed with an electroretinogram, repeated
uveitis others fundic exams at 3, 6, and 12 months are
• Greenish reflection to eye (tapetal reflection ○ Occurring after retinal reattachment indicated to assess clinical signs of progressive
in dilated pupil) ○ Chronic glaucoma retinal degeneration.
• Enlarged eye (illusion due to dilated pupil
or caused by buphthalmos)
• Polyuria/polydipsia (SARDS) DIAGNOSIS PROGNOSIS & OUTCOME
Diagnostic Overview • Permanent blindness with SARDS and PRA
PHYSICAL EXAM FINDINGS Exam of the posterior segment of the eye (i.e., • Prognosis is typically good with focal retinal
• Absence of clinical signs possible if focal fundic exam) is the cornerstone of diagnosis degeneration caused by scarring from previous
degeneration but can be difficult, and making a diagnosis posterior uveitis and/or retinal detachment,
• Generalized of retinal degeneration can be challenging. assuming disease process does not recur.
○ Often bilateral Prompt referral to a veterinary ophthalmologist
○ Dilated pupils and sluggish to absent is advisable for all cases of vision impairment PEARLS & CONSIDERATIONS
pupillary light reflexes (PLRs) or blindness of undetermined cause.
○ Vision disturbances: ranging from Comments
impaired night vision (nyctalopia) and/ Differential Diagnosis • There is no available treatment to regenerate
or impaired day vision (hemeralopia; rare) Acute, nonred, quiet-eye blindness (e.g., the retina.
(e.g., PRA) to complete blindness (e.g., SARDS): • Avoid enrofloxacin doses greater than 5 mg/
SARDS; end-stage PRA) • Optic neuritis kg/day in cats.
○ Diffuse tapetal hyperreflectivity • Optic chiasmal lesion • Maze testing can help confirm early PRA.
○ Depigmentation of nontapetum • Postchiasmal/cortical blindness (pupil size Create a maze with chairs or other objects in
○ Retinal vascular attenuation and PLRs usually normal) a small room and observe the dog’s navigation
○ With/without signs of Progressive blindness (e.g., PRA): in semi-dark and light conditions. Dogs with
Active or inactive uveitis • Slowly progressive cataracts early PRA act differently in dark conditions.
■
Glaucoma • Progressive corneal opacification
■
Cataracts Red eye blindness: Prevention
■
Systemic disease (acquired) • Glaucoma • Ophthalmic screening by a veterinary oph-
■
• Focal, multifocal • Uveitis/chorioretinitis (may have resolved) thalmologist of animals used for breeding
○ Areas of tapetal hyperreflectivity ± associ- • Lens luxation and registration through the Orthopedic
ated pigmentation • Complex corneal ulceration Foundation for Animals (www.offa.org/
○ ± Retinal vascular attenuation in affected eye_evaluation.html) can help remove PRA-
areas Initial Database and RPED-affected animals from the breed-
○ ± Signs of active or inactive uveitis Ophthalmic exam (p. 1137) ing population.
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