Uveitis in Sheep: Iritis, Painful Eyes & Causes

Uveitis is inflammation of the uvea, the vascular tissue inside the eye. In sheep, this often shows up as anterior uveitis, meaning the inflammation affects the front part of the eye, especially the iris and nearby structures. When the iris is the main area involved, people may also call it iritis. This condition is painful, can make the pupil stay small, and may lead to cloudiness, adhesions inside the eye, glaucoma, or vision loss if not treated promptly.

In practice, sheep with uveitis often look like they have a very sore eye. They may squint, tear, avoid bright light, or keep the eye partly closed. Sometimes the eye looks red. Other times it looks blue, hazy, or cloudy. Because sheep can also develop infectious keratoconjunctivitis (pinkeye), and pinkeye may occur alongside deeper inflammation, it is important not to assume every red eye is minor.

Uveitis is not one single disease. It is a sign that something is irritating or inflaming the eye. That "something" may be infection, trauma, a corneal ulcer, a foreign body, or a problem elsewhere in the body. Your vet's job is to sort out the cause and match treatment to the sheep, the flock situation, and your management goals.

One of the most common real-world causes of a painful inflamed eye in sheep is infectious keratoconjunctivitis (IKC, or pinkeye). In small ruminants, organisms linked with IKC include Chlamydia pecorum, Mycoplasma conjunctivae, Moraxella ovis, Listeria monocytogenes, Acholeplasma oculi, and Thelazia eye worms. Risk factors include flies, dust, ultraviolet light, plant awns, commingling at shows or sales, and possible trace mineral deficiencies such as copper or selenium deficiency.

Not every case starts with infection. Trauma is also common. Hay stems, foxtail-type awns, bedding, and other foreign material can scratch the cornea and trigger severe pain and secondary inflammation. A corneal ulcer can look similar to uveitis from the outside, and the two may occur together. That is one reason eye drops should never be chosen casually without an exam.

Less commonly, uveitis can be associated with systemic infection or inflammation elsewhere in the body. Chlamydial disease in sheep, for example, can be linked with conjunctivitis and may occur alongside polyarthritis in some animals. In any sheep with eye disease plus fever, lameness, poor appetite, neurologic signs, or flock-wide illness, your vet may widen the workup beyond the eye itself.

Your vet usually starts with a full physical exam and a careful eye exam. That matters because a red, painful eye can be caused by conjunctivitis, corneal ulceration, foreign material, trauma, glaucoma, or deeper inflammation such as uveitis. A presumptive diagnosis in sheep is often based on the pattern of clinical signs plus what your vet sees on examination.

The eye exam may include checking for corneal damage with fluorescein stain, looking for a plant awn or parasite, assessing pupil size and light response, and evaluating whether the cornea is clear or ulcerated. In some cases, your vet may measure eye pressure or recommend referral if the eye is very painful, opaque, or not responding as expected.

If infectious keratoconjunctivitis is suspected, samples from the eye can sometimes be submitted for culture, cytology, or molecular testing to help identify organisms involved. That can be especially helpful during outbreaks, recurrent cases, or when multiple sheep are affected. Diagnosis is not only about naming the disease. It is also about deciding how urgent the case is, whether the eye can be saved, and what level of flock management is needed.

Prevention starts with lowering the risk of eye irritation and infectious spread. Good fly control, reducing dust in pens and handling areas, and limiting exposure to sharp seed heads or awns can all help. Because infectious keratoconjunctivitis in small ruminants is associated with commingling, outbreaks are more likely after transport, sales, fairs, and shows. Quarantine and close observation of new arrivals can make a real difference.

Promptly checking any sheep with tearing or squinting is also prevention. Early cases are often easier to treat and less likely to progress to severe corneal opacity, ulceration, or rupture. If one sheep develops a painful eye, look over flockmates for milder signs and ask your vet whether group-level management changes are needed.

Work with your vet on flock health basics too. Nutrition, trace mineral balance, parasite control, and reducing stress all support eye health indirectly. There is no single prevention plan that fits every flock, so the best approach is the one that matches your region, housing, pasture conditions, and how often your sheep mix with outside animals.