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Monday, 11 May 2015

Eye Diseases in Sheep

Periorbital eczema
·         Common in the UK often resulting from cramped spacing at feed troughs and trauma to skin allows entry of S. aureus causing severe local infection. Affected sheep have markedly swollen eyelids which block vision in that eye. Ewes with both eyes affected are blind.
·         Treatment, single intramuscular injection of procaine penicillin.

Infectious Keratoconjunctivitis (IKC, contagious opthalmia, “pink eye”)
·         Often associated with adverse weather of high winds and driving snow during the winter months, giving rise to the colloquial term “snow blindness”. Large numbers of sheep can be affected; competition at feed troughs can increase rate of spread of infection. Can affect one of both eyes. Forced closure of the eyelid when sheep are exposed to sunlight. Advanced cases shows keratitis and sometimes corneal ulceration.

·         Treatment: affected sheep should be housed. Single intramuscular injection of oxytetracycline should be used. Immunity following infection is poor, lesions may re-occur.
·         Prevention methods include: providing shelter from storms. Adequate trough space and feed concentrations on the ground may limit spread. New stock (large groups) should be managed separately from the main flock.

Anterior Uveitis (Ovine Iritis)
·         Usually follows conjunctival infection with Listeria monocytogenes and is occasionally seen in sheep of all ages, especially those being fed on big bale silage.
·         Initially, the presenting signs are excessive lachrymation, forced closure of the eyelid and photophobia affecting one or both eyes. Soon after (2 – 3 days), the surface of the eye develops bluish-white opacity. Regression of ocular lesions takes weeks without treatment.
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Treatment: good results are seen when a combined injection of oxytetracycline and dexamethasone is administered by a vet.
·         Prevention/Control: limiting the contamination of silage from L. monocytogenes seems to be the most effective prevention method. Allowing exposure to air and improper fermentation provides ideal environment for the bacteria.

Entropion
·         In-turned eyelid is a common hereditary problem of many sheep breeds and cross-bred progeny. The inversion of the lower eyelid is either present at birth or appears soon after. The ocular discharge becomes purulent (containing pus) quickly. Direct contact between the eyelashes and cornea cause a severe keratitis with ulceration in some advanced cases; blindness is followed. Commonly both eyes are affected.

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Treatment: In simple cases… the lower eyelid can be everted by rolling down the skin immediately below the lower eyelid. Topical antibiotic are then applied to the cornea to control the potential secondary bacterial infection. Also, this oily substance lubricates movement of the lower eyelid and so reduces the chance of re-inversion.
If rolling fails… a subcutaneous injection of 0.5ml of antibiotic (usually procaine penicillin) is injected through the lower eyelid. The lamb should be securely held by an assistant and a 21 gauge 15mm needle introduced through the skin of the lower eyelid, parallel to and approx. 1cm below the lower eyelid. Thin metal clips can also be placed at right angles to the eyelid, to evert the eyelid.



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