Ординатура / Офтальмология / Английские материалы / Notes on Veterinary Ophthalmology_Crispin_2005

FARM ANIMAL OPHTHALMOLOGY

Figure 6.13 Severe keratitis in a ram following chronic traumatic damage from the animal’s own misdirected horn. The horn had grown too close to the eye and was removed prior to photography.

UVEAL TRACT

Neonatal uveitis

Neonatal uveitis (Figure 6.14) may be associated with, for example, umbilical infection (navel-ill), pneumonia and septicaemia in all farm animals.

Figure 6.14 Neonatal uveitis associated with navel-ill in a calf. Mild hypopyon is the most obvious feature and the eye is reasonably comfortable. Although topical symptomatic treatment for uveitis is usually given, the systemic treatment of the underlying cause is the most important aspect of management in resolution of the ocular signs.

Acquired uveitis

Uveitis may be associated with trauma, severe keratoconjunctivitis and keratitis, toxins, immune-mediated and generalised disease, including neoplasia (e.g. lymphoma). As in other species, the uveitis is termed idiopathic when a precise aetiology cannot be determined.

Malignant catarrhal fever

•Malignant catarrhal fever is a high mortality, low morbidity, pansystemic vasculopathy of ruminants caused by a herpes virus

•The virus affects all epithelial surfaces as well as vascular endothelium

•Pyrexia, generalised lymphadenopathy, oral erosions, mucopurulent nasal discharge, diarrhoea, lameness and encephalitis are possible systemic features in cattle

(b)

Figure 6.15 (a,b) Uveitis associated with malignant catarrhal fever in a Friesian steer. Note the intense pupillary constriction and loss of iris detail (right [a] and left [b] eyes). Corneal changes include peripheral cellular infiltration and vascularisation as well as mild corneal oedema. When viewed from the side the anterior chamber was relatively shallow because of the swollen, inflamed iris. (c) The left eye is shown after topical treatment with atropine and prednisolone acetate, which produced considerable symptomatic relief.

Listeriosis

•The feeding of silage (especially big bale) has been associated with uveitis (usually unilateral presentation) in cattle and sheep

•Affected animals should be taken off silage

•In neonates, listeriosis is most likely to be associated with encephalitis or septicaemia and infection is acquired from the mother’s milk

•Note that when listeriosis affects the nervous system of ruminants (notably cattle, sheep and goats), the ocular manifestations include nystagmus, blindness, facial paresis or paralysis (upper eyelid ptosis) and strabismus (usually medial and on the same side as involvement of the abducens nucleus)

Thromboembolic meningoencephalitis

•Infectious thromboembolic meningoencephalitis (TEME) is a septicaemia caused by the Gram-ve bacterium Haemophilus somnus in young cattle (commonest at less than one year of age)

FARM ANIMAL OPHTHALMOLOGY

•Of economic significance in the USA and Canada, but is apparently rare in the UK

•Ocular manifestations include conjunctivitis, retinitis (thrombosis of retinal vessels) and chorioretinitis

•Anterior segment involvement is less common

Other infectious causes of uveitis

•Toxoplasmosis can be a cause of uveitis and retinitis in sheep

•Uveitis may be associated with leptospirosis and bovine tuberculosis in cattle

•Uveitis may also be seen as part of the clinical presentation in adult animals with septic foci and septicaemia (e.g. mastitis, metritis, traumatic reticuloperitonitis and reticulopericarditis)

Signs of acute anterior uveitis

•Pain, blepharospasm, lacrimation (anterior segment triad)

•Photophobia

•Hypotony, corneal vascularisation, corneal oedema, anterior chamber infiltration, miosis, loss of iris detail and early synechiae formation

Signs of chronic anterior uveitis

Synechiae, darkening of iris, fixed, irregular pupil, iris rests, cataract, hydrophthalmos, and, sometimes, phthisis bulbi (Figure 6.16).

Figure 6.16 Phthisis bulbi following posttraumatic uveitis in a cow. Note that there is also prolapse of orbital fat.

Symptomatic treatment of anterior uveitis

•Topical corticosteroids, but avoid if corneal ulceration is present

•Topical mydriatics (1–4% atropine sulphate)

•Topical antibiotic (e.g. tetracycline)

•Intravenous or intramuscular long-acting tetracycline is useful as a first-choice antibiotic in silage-associated types, and may be effective in halting the development of uveitis if given early

LENS

Cataract

•Secondary to teratogens (e.g. BVD-MD virus), ill-defined insult (e.g. environmental factors), anterior uveitis and trauma

•Nutritional cataracts have been reported following use of the feed additive hygromycin B in pigs

OCULAR FUNDUS

ANATOMY

The optic nerve head is often myelinated and of variable shape and size in farm animals, and may be heavily pigmented in sheep. It is usually located within the nontapetal fundus.

The retinal blood supply is holangiotic. The 3–4 primary retinal vessels are large and very distinct, and it is not unusual to find that the dorsal arteriole and venule spiral around each other. The small choroidal vessels (mainly capillaries) that perforate the tapetum en route for the choriocapillaris can be viewed ophthalmoscopically as distinct dark dots – the stars of Winslow.

The tapetum of herbivores, yellow, green or blue in colour, is formed from collagen (tapetum fibrosum) and this forms an effective barrier, so that in herbivores generally it is often easier to identify fundus pathology by examining the non-tapetal fundus. Pigs do not have a tapetum, and the fundus is a uniform light grey to redbrown colour in most pigs and of pinker appearance when less pigment is present.

Figure 6.17(a–d) Normal bovine fundus (a), ovine fundus (b), caprine fundus (c) and camelid fundus (d).

FARM ANIMAL OPHTHALMOLOGY

(a)

(c)

(b)

Figure 7.1(a–c) Normal gross equine globe (a); fundus (b); cornea and dorsal iris and granula iridica (c) (with acknowledgements to J. R. B. Mould).

EQUINE OPHTHALMOLOGY