Page 288 - Cote clinical veterinary advisor dogs and cats 4th

124 Blindness

DIAGNOSIS ■ Evaluate tapetum for brightness and/ mass or uveitis, chorioretinitis are noted and/
or if optic neuritis is suspected)
or color changes (hyperreflective/ • Serologic titers for infectious diseases if
VetBooks.ir Lesion localization is the cornerstone of accurate or certain forms of retinal detachment; presence in/travel to endemic area: rickettsial
Diagnostic Overview
bright with retinal degeneration and/
hyporeflective/dull gray to pigmented
diseases (particularly if intraocular hemor-
diagnosis and treatment. Complete cranial nerve
and general neurologic exams are an essential
forms of retinal detachment).
if chorioretinal lesions with uveitis and/or
first diagnostic step. If the cause of blindness is with subretinal inflammation, certain rhage is noted), systemic mycoses (particularly
not readily apparent, referral of affected patients ■ Evaluate nontapetal fundus (located optic neuritis are detected), borreliosis (if
to a veterinary ophthalmologist is advised. Early ventrally and typically pigmented) for history of tick exposure + uveitis), bartonel-
diagnosis is key to determining whether return whitish or gray discoloration (e.g., losis (if history of flea exposure + uveitis),
of vision with therapy is possible. edema, inflammatory exudate, depig- and toxoplasmosis (if history of rodent
mentation from active or past inflam- exposure + chorioretinal lesions)
Differential Diagnosis mation or retinal detachment) or • Aspiration of enlarged lymph nodes for
Red eye blindness: hemorrhages. cytologic evaluation
• May be confused with disorientation due to ■ Evaluate vasculature of retina (should • Ocular ultrasonography if opacity of ocular
causes other than blindness (p. 268) and see small arteries and larger veins media precludes fundic exam
concurrent non–vision-threatening causes of coming from the optic disk and cours- • Histopathologic evaluation in cases when
red eye, including conjunctivitis, episcleritis, ing peripherally), and look for changes eye is blind and painful and enucleation is
and corneal disease (p. 870) in vessel direction to indicate detach- advised
Non–red, non–inflamed eye blindness: ment or attenuation (thinning) to • Referral is advisable for all cases of blindness of
• May be confused with disorientation due to indicate degeneration. undetermined cause for additional evaluation,
causes other than blindness • CBC, serum chemistry profile, urinalysis to including one or more of the following:
Unilateral versus bilateral: assess systemic status ○ Electroretinography to assess retinal
• Unilateral: ocular trauma, complex corneal • Blood pressure measurement with retinal function
ulceration, lens luxation, cataract, severe hemorrhage and/or detachment ○ Cerebrospinal fluid tap
uveitis, retinal detachment, subretinal hemor- ○ Advanced imaging (computed tomography
rhage, glaucoma, cerebral lesions (optic Advanced or Confirmatory Testing or magnetic resonance imaging)
radiation/visual occipital cortex) • Thoracic radiographs (screen for neoplasia ○ Vitreous centesis with cytology, culture,
• Bilateral: cataracts, retinal detachment, sub- or systemic infectious disease if intraocular titers
retinal hemorrhage, severe uveitis, glaucoma,
optic neuritis, optic chiasm lesions, sudden
acquired retinal degeneration, progressive
retinal degeneration/atrophy, diffuse cerebral/
visual cortex disease
Initial Database L M M L
The essential first step for lesion localization is Visual Pathway
to perform a complete neurologic exam (p.
1136) and ophthalmic exam (p. 1137).
• Important neuro-ophthalmic findings in a
blind patient
○ Normal PLRs: lesion is usually postchiasmal/
cortical (with a non–red, non–inflamed
eye blindness) or due to opacity of ocular Ciliary
media ganglia
○ Sluggish, incomplete/absent PLR and
dilated pupil: lesion involves retina, optic
nerve, optic chiasm (causes bilateral Optic nerve Optic chiasm
blindness), or optic tract, or a separate,
primary lesion of the pupil is present.
○ Chromatic PLR testing Optic tract
Absent red light/positive blue light PLR:
■
lesion involves photoreceptors (e.g.,
PRA, sudden acquired retinal degenera- Lateral geniculate nucleus
tion [SARD], retinal detachment)
Absent red and blue light PLR: lesion
■
involves optic nerve (e.g., optic neuritis)
• Important elements of the ophthalmic exam Pretectal nucleus
in a blind patient
○ Intraocular pressure assessment
○ Exam of anterior segment Edinger Westphal
Evaluate for opacity of the cornea,
■ nucleus
aqueous humor, lens, or vitreous
○ Posterior segment/fundic exam after phar- Visual cortex
macologic pupil dilation (1% tropicamide)
Pharmacologic pupil dilation is con-
■
traindicated with glaucoma. BLINDNESS Anatomy of visual pathway from the eye to the visual cortex of the cerebrum. Circles adjacent
Evaluate optic nerve (size, shape, color).
■ to the visual pathway title indicate visual fields. L, Lateral; M, medial.
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