Page 1227 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1202 CHAPTER 11

VetBooks.ir help decrease optic nerve swelling and inflammation. Table 11.11 Causes of optic neuritis
There is no treatment available for chronic cases.

Prognosis • Idiopathic/immune-mediated
• Fungal
The prognosis for restoration of vision is guarded to • Systemic aspergillosis, Cryptococcus neoformans
poor, as it is often a permanent condition. • Toxoplasma gondii
• Onchocerca cervicalis
EXUDATIVE OPTIC NEURITIS/ • Leptospira spp.
NEUROPATHY • Neoplasia
• Toxins
• Lead, arsenic, thallium, ethyl/methyl alcohol, chlorinated
Definition/overview hydrocarbon?
Exudative optic neuropathy is seen as a sudden onset • Sepsis
of unilateral or bilateral blindness in middle-aged or • Other bacterial
older horses. The most prominent finding is marked • Streptococcus equi, Actinomyces spp., Actinobacillus
exudation with/without haemorrhages present over equuli, Rhodococcus equi
the surface of the ONH, accompanied by blindness • Vitamin A deficiency?
• Orbital inflammation
in affected eyes. • Trauma
• Vascular compromise/ischaemia
Aetiology/pathophysiology • Borna disease
The cause is unknown, and the pathophysiology is • Parasite migration
unclear. The exudate contains proliferating astro- • Brain abscess/meningitis caused by Pseudomonas mallei
cytes and lipid-laden phagocytic cells. (glanders), Streptococcus equi, cryptococcosis
• Equine protozoal encephalomyelitis
• Hepatoencephalopathy, leucoencephalomalacia,
Clinical presentation hydrocephalus, idiopathic epilepsy
Acute blindness is seen in affected animals. The retinal • Verminous migration
lesions seen on fundoscopy may vary but are typically • Profound blood loss
seen as white to grey exudates that radiate from the • Rabies
ONH and are raised into the vitreous. The exudate may
obscure the ONH completely. If the ONH is visible,
oedema and multiple small haemorrhages are often pres- Management
ent. With chronicity the ONH will appear atrophied. Treatment is not successful.

Differential diagnosis Prognosis
Sepsis and other causes of optic neuritis (Table 11.11), The prognosis is generally poor because the ONH
traumatic optic neuropathy, benign exudative/ lesions will typically progress to atrophy.
proliferative optic neuropathy and ONH tumours
should be included in the list of differentials for BENIGN PROLIFERATIVE
exudative optic neuritis. OPTIC NEUROPATHY

Diagnosis Definition/overview
Diagnosis is based on history and clinical findings Benign proliferative optic neuropathy describes
(Fig. 11.112). Exclusion of optic neuritis as a dif- white or grey material protruding anterior to the
ferential requires a neurological examination and optic disc and into the vitreous in an otherwise nor-
additional investigations that may include serology mal fundus. The exudate may slowly enlarge over
and toxicological testing, ERG, cerebrospinal fluid months or years; however, there is no or minimal
sampling and CT/MRI. effect on vision (unless it becomes large enough to