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Blindness 123

• Bandages contaminated with exudates should • Yeast form found in animal tissues is not AUTHORS: Andrea Dedeaux, DVM; Joseph Taboada,
be disposed of as infectious waste (inciner- • Can be transmitted by penetrating wounds DVM, DACVIM
directly transmissible.
EDITOR: Joseph Taboada, DVM, DACVIM
VetBooks.ir low because of the specific conditions SUGGESTED READING Diseases and Disorders
ated), but the likelihood of aerosolization is
Blastomyces organisms require to grow.
Client Education Dedeaux, AM, et al: Blastomycosis and histoplas-
mosis. In Ettinger SJ, et al, editors: The textbook
• Long-term treatment is necessary. of veterinary internal medicine, ed 8, St. Louis,
• Can be fatal despite treatment 2017, Saunders, pp 1027-1035.

Blindness Client Education
Sheet

BASIC INFORMATION • In cases of sudden blindness, some or all of ❏ Menace response is usually present
the following may be reported: in the ipsilateral eye.
Definition ○ Disorientation ○ Menace response may be absent
Loss of vision ○ Suddenly starts bumping into objects in the nasal visual field due to loss
○ Inability to find food bowl, toys of the small percentage of lateral
Synonyms ○ Lethargy, anxiety undecussated fibers.
Blindness due to central nervous system dis- • In cases of progressive blindness, some or ■ Menace response absent in both eyes
orders is also called amaurosis or central all of the following may be reported: in bilateral/diffuse optic tract, lateral
blindness. ○ Occasionally bumping into objects in own geniculate nucleus, optic radiation, or
environment visual cortical lesions
Epidemiology ○ Frequently bumping into objects in ■ Pupil size and PLRs are normal with
SPECIES, AGE, SEX unfamiliar environments central disease because PLR fibers
Dogs and cats, any age, either sex ○ Vision deficits in dim light and/or darkness separate from the vision pathway just
(e.g., progressive retinal atrophy [PRA]) before the LGN.
GENETICS, BREED PREDISPOSITION ○ Patients may be lethargic and/or anxious ❏ Exceptions: a concurrent iris disorder
Depends on causative disorder but generally adjust and compensate better exists
with more slowly progressive vision loss. ■ Subtle anisocoria may occur with optic
RISK FACTORS tract lesions before the LGN (i.e.,
• Age: older animals may be predisposed to PHYSICAL EXAM FINDINGS contralateral pupil more dilated).
blindness associated with optic chiasmal • See Neurologic Examination (p. 1136) and ■ Dazzle reflex(es) normal (dazzle reflex
neoplasia (p. 559), cataracts (p. 147), and Ophthalmologic Examination (p. 1137). does not involve the visual cortex)
retinal detachment (p. 885). • Red eye blindness (p. 870)
• Outdoor access may predispose to infectious • Non–red eye blindness Etiology and Pathophysiology
diseases and/or toxins associated with ○ Prechiasmal/chiasmal lesion Red eye blindness: the lesion is ocular or
blindness. ■ Menace response (blink in response to intraocular:
hand motion toward the eye) absent • Opacity of the ocular media (e.g., cornea,
Clinical Presentation
■ Dazzle reflex (blink in response to a aqueous humor, lens, vitreous) in cases of
DISEASE FORMS/SUBTYPES bright light) decreased (i.e., sluggish) corneal edema/ulceration/pigmentation, uveitis,
• Unilateral or bilateral or absent cataract and vitreal debris or hemorrhage
• Sudden or progressive ■ Pupil(s) dilated +/− fixed/unresponsive • Retinal degeneration with or without detach-
• Red eye blindness: associated with visible ■ Pupillary light response (PLR) decreased ment and optic nerve atrophy in glaucoma
conjunctival redness on physical exam (i.e., sluggish and incomplete) or • Retinal detachment in cases of chorioretinitis
○ Glaucoma (p. 387), severe uveitis (p. absent. Consensual PLR refers to reac- Non–red eye blindness:
1023), cataracts (p. 147), lens luxation tion of contralateral eye when ipsilateral • Prechiasmal/chiasmal lesion: lies along the
(p. 581), complex corneal ulceration (p. eye is illuminated (e.g., absent consen- retina–optic nerve–optic chiasm pathway
209), orbital disease (p. 716) sual PLR of the right pupil in response ○ Retinal diseases (pp. 883 and 885)
• Non–red, non–inflamed eye blindness: no to light shone into the left eye). ○ Optic nerve lesions (e.g., congenital optic
conjunctival or scleral redness is observed ■ ± Anisocoria (asymmetry between the nerve hypoplasia, inflammation), neoplasia
in the blind eye(s) size of the pupils) (e.g., meningioma), or atrophy (e.g.,
○ Prechiasmal/chiasmal blindness; lesion ○ Postchiasmal/cortical lesion glaucoma, trauma)
affecting retina, optic nerve, optic chiasm ■ Menace response variable depending ○ Optic chiasmal lesions (e.g., neoplasia,
○ Postchiasmal/cortical blindness; lesion on localization and severity of lesion abscess)
affecting optic tracts, lateral geniculate ■ If a unilateral lesion is present • Postchiasmal/cortical lesion: affects the optic
nucleus (LGN), optic radiations, or visual ❏ Menace response is absent or tract and/or radiations to and including the
cortex of the cerebrum decreased in the contralateral eye visual (occipital) cerebral cortex
○ Small percentage of contralateral ○ Encephalitis (extension to bilateral optic
HISTORY, CHIEF COMPLAINT nasal/medial visual field may be tracts through cerebrospinal fluid)
• Depends on the cause, whether the blindness preserved due to undecussated ○ Cerebral edema
is unilateral or bilateral, and sudden or (those not crossed over) lateral ○ Cerebral infectious, inflammatory, neo-
progressive in onset optic nerve fibers plastic, or traumatic disease

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