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Neuroophthalmology

Bradford J. Holmberg, DVM, MS, PhD, DACVO

Animal Eye Center, Little Falls, NJ, USA

Neuroophthalmology is a complex discipline involving Optic Neuritis
the intricate relationship between the eye and the central
nervous system (CNS). A thorough understanding of Inflammation of the optic nerve is usually bilateral and
afferent and efferent pathways is crucial in the loca­ results in complete vision loss with the absence of pupil­
lization and diagnosis of neuroophthalmic disorders. lary light reflexes. On ophthalmic exam, the optic disc is
A review of normal anatomy and physiology is beyond enlarged and hyperemic with focal hemorrhages and
the scope of this chapter and can be found elsewhere. peripapillary retinal detachment (Figure 77.1). If only the
Abnormalities in the afferent or efferent arm may pre­ retrobulbar optic nerve is affected, the ophthalmic exam
sent as changes in vision, eye position, tear production, will be normal and diagnosis is confirmed through a
eyelid carriage, function, sensation, and pupil shape, size normal ERG and abnormal MRI. T2‐weighted MRI may
or response. This chapter will focus on common neu­ reveal an enlarged, moderately hyperintense optic nerve.
roophthalmic diseases. CSF analysis in dogs with optic neuritis is variable and
may reveal a marginal to marked increase in protein or
cellularity.
Amaurosis Optic neuritis can be secondary to infectious, inflam­
matory, and neoplastic disease. In dogs, infectious causes
Amaurosis is defined as partial or complete vision loss include viral (distemper and tick‐borne encephalitis
without observable ophthalmic pathology. Clinical signs virus), fungal (cryptococcosis, blastomycosis, histoplas­
of vision loss include a reduced or absent menace mosis), protozoal (toxoplasmosis), and bacterial (ehrli­
response, inability to track a cotton ball, failure to navi­ chiosis). Granulomatous meningoencephalitis is the
gate around stationary objects, and possibly an absent most common inflammatory disorder, although idio­
dazzle reflex or pupillary light reflex (PLR). Amaurosis pathic and necrotizing meningoencephalitides have also
may be caused by primary retinal disease, such as sudden been reported. Primary optic nerve tumors and space‐
acquired retinal degeneration syndrome (SARDS), ret­ occupying retrobulbar masses may trigger secondary
robulbar optic nerve disease, or any lesion along the nerve inflammation. In cats, optic neuritis is often sec­
optic chiasm, optic tract, lateral geniculate nucleus, ondary to feline infectious peritonitis, but may be due to
optic radiation, or visual cortex. Electroretinography other infectious diseases, including cryptococcosis and
(ERG) is essential in differentiating retinal disease from toxoplasmosis. Most cases of optic neuritis are consid­
CNS disease as ERG will identify a retina that appears ered idiopathic due to lack of an apparent cause even
normal on examination but fails to function properly. with a thorough systemic medical work‐up.
Frequently, magnetic resonance imaging (MRI) and cer­ Treatment of optic neuritis is directed at the underlying
ebrospinal fluid (CSF) analysis are instrumental in diag­ cause when feasible. If no underlying cause is identified,
nosing a primary CNS cause of vision loss. Neoplasia is immunosuppressive doses of corticosteroids are used to
the most common CNS cause of vision loss in dogs and reduce inflammation. Even with appropriate therapy,
cats. Prognosis for return of vision is grave with SARDS prognosis for return of vision is poor and optic nerve
and poor with CNS disease, depending on the underlying atrophy is an unfortunate common end‐result.
etiology.

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical