Tackling farm animal ophthalmology

Anterior uveitis

This is mainly a problem in cattle, but it does also occur in sheep. It is always associated with feeding silage – usually in roundbale feeders, where the animals put their heads deep into the silage. The cause is thought to be Listeria monocytogenes. This organism can be isolated from corneal swabs. However, the condition does not progress to the systemic disease of listeriosis. Several animals may be affected. The uvea cannot be examined as the cornea is opaque, and one or both eyes may be affected. There is a profuse ocular discharge from affected eyes.

Treatment is aimed at reducing inflammation, and systemic antibiotics and steroids have been suggested. However, I have had good experience with subconjunctival injections of dexamethasone and atropine (to dilate the pupil) in cattle. I have never used this treatment in sheep. Sadly, farmers should be warned that the condition may occur again long after silage feeding has ceased.

I have not performed any clinical audit, but perhaps long-term systemic oxytetracycline therapy at the time of the subconjunctival injection might give a more lasting cure. I have found 48-hour eye ointment with a variety of antibiotics to be ineffective.

Bovine malignant catarrh

Sheep in the UK spread this systemic viral disease in cattle, but I have also had experience with the virus in Maasailand during the wildebeest migration. Cattle have a raised temperature and show respiratory signs of the disease. However, the most obvious sign is a profuse ocular discharge and corneal opacity.

There is no suitable treatment, and mortality in animals showing symptoms is high. However, in my experience, there is a very low morbidity, unlike rinderpest, which shows similar muscle erosions, but not nearly so marked ocular opacity. I have never seen this condition in the UK. I am sure readers would welcome some first-hand experience from any colleagues.

Bright blindness

This condition is seen in sheep from chronic bracken poisoning. The pupils are dilated and the cornea is clear, but there is no response to light. This is a selflimiting condition if the sheep are moved off the bracken.

Entropion

This condition in sheep is almost certainly hereditary. However, that is difficult to prove in crossbred sheep. It is usually present at birth, but is often not noticed for a couple of days. Normally, the bottom eyelid is rolled inwards. Occasionally, the top eyelid is involved as well. If the condition is seen early enough it is often sufficient to just roll the affected eye outwards and it will remain in the correct position. If the condition is neglected, however, more radical treatment needs to be initiated to prevent the loss of the eye and considerable pain.

There are various treatments advocated. I am proud to say that my partner, Sam Ellis, wrote up a treatment in The Veterinary Record in 1938. This consisted of injecting a bleb of liquid paraffin under the eyelid to keep it away from the cornea. Others have subsequently injected antibiotics. A further treatment is to put in a suture to take a tuck out of the eyelid. As soon as the irritation on the cornea is removed the eye heals very quickly.

Foreign bodies

This is mainly a problem in cattle fed on oat straw from racks, although other foreign bodies can get blown into eyes of all farm animals. It is vital that the entire foreign body is removed to prevent suffering and allow the eye to heal. Firstly, it is better to get a large bovine animal into a crush. If the animal is not easily handled, I would advise a small dose of xylazine (2ml of a two per cent solution) intramuscularly. This dose may need to be increased in a really fractious animal. It could also be given into the tail vein if the product is licensed for that route.

After securing the animal with a stout halter, and perhaps a pair of bulldogs, I would try to apply some local anaesthetic into the eye. In the past I have used a small plastic bottle of Willocaine; however, this is no longer available. I now use Intubeaze (Dechra), which is a spray to aid the intubation of cats. However, it also works well in the eyes of cattle and does not sting the animal like normal injectable solutions. Removing the foreign body is normally straightforward by using a pair of dressing forceps. I have never had to block the eyelids, although sometimes I have had to instil more local anaesthetic into the eye. I usually complete the treatment by installing a subconjunctival injection of antibiotics.

Infectious bovine rhinitis

This widespread viral disease of cattle causes respiratory and genital infections. Ocular lesions are not so marked as they are in bovine malignant catarrh, so often amount to a low-grade conjunctivitis. The eyes directly, therefore, do not need treating – only the whole animal.

Infectious keratoconjunctivitis

I first came across this contagious condition in cattle in 1964 in Wiltshire; it was then called “New Forest eye”. The condition then moved slowly eastward, so that, by the time I returned from Africa in 1975, it was just reaching north Norfolk. In cattle it appears to be spread by flies, and is, therefore, considered a summer condition. On the other hand, the same condition, “pink eye”, occurs in sheep during the winter and is associated with adverse weather conditions.

Koch’s postulates have never been fulfilled in this condition. Chlamydophila psittaci and Mycoplasma conjunctivae have both been found. The condition starts with conjunctivitis in one or both eyes. This can then progress to severe inflammation of the cornea and the sclera. The eye becomes opaque and there is often infection and pus in the anterior chamber. There is conflicting evidence in the literature as to treatment and results. Some authorities consider the condition to be self-limiting in 95 per cent of cases, so many treatments appear to be effective. I believe when there is pus in the anterior chamber, self-resolution is unlikely. Indeed, even with treatment, the eye may be lost.

The farmers’choice for treatment in cattle is long-acting eye ointment containing broadspectrum antibiotics. In sheep, farmers tend to want to use systemic long-acting oxytetracylcine injections. These are also used in cattle, but are rather costly for widespread use. The treatment I use is a subconjunctival injection of oxytetracycline. However, this is rather labour-intensive if the problem is widespread.

Squamous cell carcinoma

This can occur in all farm species. It usually starts on the third eyelid and progresses to the conjunctiva. It is important to try to remove the third eyelid before the tumour has progressed.

This is a simple task when using a pair of curved scissors and a pair of rat-toothed dressing forceps. Naturally, the animal is best sedated in a crush with the eye and conjunctiva anaesthetised with local anaesthetic. It is important to remove as much of the margin around the tumour as possible. These tumours are normally restricted to the third eyelids in all species that are lacking in pigment. The sun increases the incidence of the problem, as does fly worry. Therefore, fly control is beneficial. Genetics play a role in prevention in the tropics.

Trauma

Trauma is usually self-inflicted following an eye infected with infectious keratoconjunctivitis or an eye containing a foreign body. Removing the animal to a place where self-trauma will be difficult should prevent this. Systemic non-steroidal anti-inflammatory drugs (NSAIDs) can be given to help reduce the inflammation.

Vitamin A deficiency

The textbooks describe this condition as rare – indeed, I have only seen two cases. Both were bulls on the same farm being fed a diet of barley straw and rolled barley with no additives. They were immature stock bulls kept in individual pens.

Normal signs are reputed to be an ocular discharge with corneal opacity. However, in these two cases, there was total blindness with retinal degeneration. Neither injections of vitamins A, D and E, nor supplementary food additives containing vitamin A, brought back the sight.

Ocular enucleation

I have left this to last as, sadly, it is an admission of treatment failure. However, in many cases, it is much kinder for the animal. It is unlikely to be performed, except in cows or pet ruminants, because of the cost. The method is fairly standard and is recorded in most textbooks.

The animal should be very heavily sedated. The whole area of the eye and eyelids should be blocked with local anaesthetic and 10ml should be injected into the optic nerve – with a two-inch needle in cows. The eyelids are then stitched together and the whole area cleaned and prepared aseptically. An incision is made through the skin, but not into the conjunctiva, parallel to the eyelid suture line. With blunt dissection, the musculature is separated between the conjunctiva containing the eye and the socket. Eventually, a long pair of curved artery forceps can be inserted to grasp the optic nerve and attached vessels. The eye and sutured eyelids are then removed and the vessels ligated. The skin is then sutured.

I have not found any satisfactory way to fill the dead space left after removal of the eye. I know some surgeons pack the hole with sterile gauze, which is then slowly removed, daily. Obviously, large doses of antibiotics and NSAIDs should be given for a minimum of 10 days.

Usually, you will be rewarded by a very rapid improvement in the demeanour of the animal, even if there is some sepsis and wound breakdown.

Acknowledgement

I would like to thank Sam Ellis and my other two mentors, Alec Dawson and John Gittins, for inviting me into their practice. I have been able to pass on so many of their tips to you through the pages of Veterinary Times.