Anterior uveitis in dogs: symptoms, causes and treatment

Overview

The iris forms the coloured ring around the pupil. It controls the amount of light entering the eye by changing pupil size. The ciliary body behind the iris produces most of the clear fluid in the front of the eye, called aqueous humour. This fluid carries nutrients to tissues at the front of the eye. It also helps remove their metabolic waste. Aqueous humour returns to the circulation through the drainage angle between the cornea and iris.

Inflammation allows more protein and cells than usual to enter the aqueous humour. This makes the normally clear fluid look hazy under the examination light. Inflammation can extend to the choroid at the back of the eye.

Causes

Inflammation starting within the eye

A blunt impact can cause anterior uveitis even without a penetrating wound. A corneal ulcer can also trigger inflammation inside the eye through a nerve-mediated response. An intraocular tumour can cause local inflammation. A displaced or unstable lens can also inflame the front of the eye.

As a cataract progresses, proteins may leak from the lens and trigger inflammation. Rupture of the lens capsule can suddenly expose the eye to a large amount of lens material. The resulting inflammation can be difficult to control with medication.

Disease starting elsewhere in the body

Inflammation in both eyes can be associated with a wider disease, such as infection or an autoimmune disorder. Lymphoma can cause intraocular inflammation as part of cancer elsewhere in the body. Tick-borne ehrlichiosis is one possible infectious cause. Inflammation is called idiopathic when investigations leave the underlying cause unknown.

A hospital series investigated uveitis causes in 102 dogs whose inflammation was unrelated to trauma or hypermature cataracts. Of these cases, 58% were classified as idiopathic or immune-mediated. A tumour was identified in 25 dogs, or 24.5% of the group. Lymphoma was the most common associated tumour in this series, identified in 17 dogs. Infectious inflammation was diagnosed in 18 dogs, or 17.6%.

Risk factors

A rapidly progressing cataract can cause a stronger inflammatory response than a slower change. Lens-induced uveitis also occurs with diabetic cataracts. Among 151 dogs with lens-induced uveitis, the average interval between noticing the cataract and onset of inflammation was 17 months. In the same hospital series, the average interval was 25 months in Poodles and 11 months in American Cocker Spaniels.

A slowly progressing pigmentary uveitis is recognised in Golden Retrievers. Iris and ciliary body cysts in this breed may be associated with pigment release and chronic uveitis. Eye examinations of 630 Golden Retrievers in western Canada identified pigmentary uveitis in 37 dogs, or 5.9%. Among dogs over 4 years old, 32 of 251 were affected, or 12.7%. A United States study found pigmentary uveitis in 9 of 164 Golden Retrievers, or 5.5%. Of 23 dogs with a thin-walled, attached cyst, 13 had pigmentary uveitis or associated glaucoma on re-examination. In uveodermatological syndrome, which involves loss of skin pigment, inflammation can affect the entire uveal tract. In a hospital series of 50 dogs with this syndrome, 37 were Akitas.

Typical symptoms

• Your dog squints because of involuntary eyelid spasm.
• Bright light bothers your dog more than usual.
• Much of the white of the eye may look red.
• The pupil in the painful eye may be smaller than usual.
• Corneal swelling can make the eye look cloudy.
• The iris can swell during inflammation.
• Blood may be visible in the front of the eye, in front of the pupil.
• Irritation may make the eye water more than usual.
• Fibrin sometimes accumulates in the front chamber and can be seen during slit-lamp examination.

With prolonged inflammation, the pupil may become irregularly shaped. Early signs can resemble conjunctivitis or corneal inflammation. In chronic uveitis, new blood vessels may grow onto the corneal surface from its edges.

Complications and consequences

Raised eye pressure and sight damage

Inflammatory material can obstruct the drainage angle through which aqueous humour leaves the eye. Reduced drainage can raise pressure and lead to secondary glaucoma. Glaucoma can persist after inflammation settles if the drainage pathway is permanently scarred. In a study of hospital eye patients, glaucoma was diagnosed in 17% of dogs whose primary diagnosis was anterior uveitis.

Prolonged inflammation can create adhesions between the iris and lens. The lens may become cloudy as a result of inflammation, forming a cataract. Following severe or recurrent inflammation, the eyeball may shrink.

A follow-up study of Golden Retrievers with pigmentary uveitis included 29 dogs. At an examination at least 6 months later, 48 of 57 examined eyes retained sight. Of the 9 eyes that lost sight, 7 became blind because of glaucoma. Adhesions between the lens and iris were associated with an increased glaucoma risk in this group.

Among 50 dogs with uveodermatological syndrome, 18 already had glaucoma at their first visit (36%). Of the dogs whose sight was assessed initially, 26 of 46 were blind in both eyes.

Diagnosis at the vet

Examining both eyes

Your vet asks when symptoms began and whether an eye injury could have occurred. Both eyes are assessed even if you noticed changes in only one. Pupil responses and reflexes are part of the basic examination. The narrow beam of a slit lamp helps reveal cloudiness in the aqueous humour. In the 102-dog uveitis series, 88 dogs had aqueous humour cloudiness. Your vet also examines the back of the eye because inflammation may extend there. Fluorescein staining checks for a concurrent corneal ulcer. However, a narrow penetrating corneal wound caused by a cat's claw may initially fail to take up dye.

Eye pressure is usually low in acute anterior uveitis. Pressure below 10 mmHg supports suspected uveitis alongside other eye findings. A pressure difference of 5–10 mmHg between the eyes can also indicate inflammation. However, pressure may be normal or raised if inflammation obstructs drainage.

Ultrasound helps assess the back of the eye when cloudiness at the front obscures the view. In one eye injury case, ultrasound identified a penetrating injury to the front lens capsule when corneal cloudiness prevented examination of the internal structures. In pigmentary uveitis, your vet looks for radial or band-like pigment deposits on the front lens capsule.

Investigating the underlying cause

Blood tests may reveal evidence of disease elsewhere if the eye examination does not establish the cause. Your vet can choose targeted infection tests according to the eye findings. A fine-needle sample from an enlarged lymph node can help investigate lymphoma. Chest X-rays or abdominal ultrasound may help establish the extent of a suspected systemic disease.

Treatment

Treating inflammation and pain

Treatment aims to relieve pain while controlling inflammation inside the eye. Your vet chooses an anti-inflammatory eye medicine according to corneal condition and the cause of inflammation. Corticosteroid drops can worsen a corneal ulcer and delay its healing.

A pupil-dilating medicine can relieve eye pain and keep the pupil mobile. Raised pressure influences this choice because medicines such as atropine can worsen glaucoma. When the infection causing inflammation is identified, treatment targets that organism. Systemic corticosteroids are considered once infection and tumours requiring chemotherapy have been ruled out. Immune-mediated inflammation may require medication affecting the whole body's immune response.

Surgery and follow-up

If a penetrating injury damages both the cornea and lens, lens removal surgery may help preserve sight. In one study, 85.2% of 27 dogs undergoing this surgery retained sight at their last check. Median follow-up was 8 months. In all dogs that lost sight, the change was identified within 14 weeks of surgery.

Eye pressure is measured during treatment because glaucoma can develop after inflammation. Re-examinations also assess whether inflammation is settling and look for other complications. Recurrent uveitis may require long-term topical or oral medication. If an eye is blind and remains painful because of severe complications, it can be removed to relieve pain. In an owner survey after eye removal for glaucoma, owners noticed the greatest improvement in their dogs' behaviour at 2 months.

Prevention

Combination vaccines including protection against infectious canine hepatitis are available for dogs; product availability differs between countries. Infectious canine hepatitis is one infection that can cause uveitis. Protecting a dog travelling abroad against ticks reduces the risk of infections they transmit, such as ehrlichiosis. Check your dog's coat after returning from travel, particularly for brown dog ticks.

Monitoring cataracts helps detect lens-induced inflammation, to which advanced cataracts particularly predispose dogs. The European College of Veterinary Ophthalmologists recommends annual official eye examinations for breeding dogs to detect inherited eye diseases. A thin-walled cyst attached to the iris or ciliary body in a Golden Retriever warrants follow-up eye examinations.

Important for dog owners

Do not put old corticosteroid drops into a painful eye because a corneal ulcer may be present. If a stick or another object is lodged in the eye, prevent rubbing and seek emergency care. Leave an embedded object for the vet to remove.

Wash your hands before and after giving eye medication. Keep the bottle tip away from your dog's eye and eyelids. Let your dog blink after a drop so the medicine spreads over the surface. If the eye becomes redder or looks more irritated after drops, contact the vet treating your dog.

Frequently asked questions

How does anterior uveitis differ from conjunctivitis?

Anterior uveitis affects the iris and ciliary body inside the eye. Redness can resemble superficial conjunctivitis, particularly early in the inflammation. Your vet uses a slit lamp to look for haze in the normally clear fluid of the front chamber. A corneal ulcer can cause similar symptoms and is checked with fluorescein dye.

Can anterior uveitis spread to another dog?

Inflammation inside the eye triggered by injury or cataracts does not spread between dogs. However, some infections causing uveitis can spread to other animals. Ehrlichiosis is transmitted by ticks, so tick protection is important in preventing that infection.

Can eye pressure be high despite anterior uveitis?

Yes. Inflammation can obstruct aqueous humour drainage and raise pressure. High pressure may become permanent if inflammation damages the drainage pathway. Measuring pressure during treatment helps detect glaucoma that may develop as a consequence.

Can cataracts both cause uveitis and result from it?

As a cataract progresses, proteins leaking from the lens can trigger intraocular inflammation. Conversely, longstanding anterior uveitis can itself cause cataracts and adhesions between the iris and lens. Slit-lamp examination helps establish which part of the eye is cloudy.

When should an inflamed eye be re-examined?

Your vet arranges a re-examination to assess response and possible complications. If the eye suddenly becomes cloudy or your dog keeps it closed, contact an emergency vet immediately. Sudden deterioration in sight also requires urgent assessment.