Keratitis

What is keratitis?

Keratitis is a common disease of the equine eye that involves inflammation of the cornea, the clear, outer layer at the front of the eye. Causes can include injury or foreign bodies.

The cornea is composed of multiple layers, with the outermost layer comprised of cells that keep the cornea dehydrated and transparent. The cornea acts as a barrier to protect the eye from debris and germs and focuses light on the retina at the back of the eye.  A healthy cornea is important for proper vision.

“Keratitis” is often an umbrella term for corneal disease, and is broadly classified as ulcerative or non-ulcerative, each with their own subgroups. Corneal ulcers are erosions in the cornea. Once this protective barrier is compromised, there is not much separating the inner eye from environmental hazards like bacteria, fungi, and viruses. Corneal ulcers appear suddenly, progress rapidly, and are often painful. Cases are further classified based on the depth and position of the ulcer.

The cornea remains intact in cases of non-ulcerative keratitis. Cases are often caused by an immune response to proteins or antigens. This category may be further classified as infectious, including stromal abscesses, or non-infectious, such as immune-mediated keratitis (IMMK). Some types of non-ulcerative keratitis (such as IMMK) are usually less painful, while other (such as stromal abscesses) can be extremely painful.

What are the clinical signs of keratitis?

Clinical signs of keratitis are numerous and can include squinting, watery eyes, constricted pupils, pain, a white or bluish cloudy appearance to the surface of the eye, a swollen, red eye, and ocular discharge.

How is keratitis diagnosed?

Diagnosis of keratitis is usually based on clinical signs and a thorough ocular examination. Dye (fluorescein) staining may be used to determine if there are ulcers on the cornea. Swab for culture, scraping for cytology, or biopsy samples may be obtained and submitted to a laboratory to identify if bacteria or fungi are present.

How is keratitis treated?

Treatment for keratitis varies by type and cause. Medical treatment is common and may include topical and/or oral medications such as antibiotics, antifungals, atropine, anti-inflammatories, and anti-proteinases. A subpalpebral lavage (SPL) system may be utilized to administer drugs on a frequent basis. The horse may need to wear a protective visor while the eye heals. Surgical approaches, including corneal grafts and transplantations or enucleation (removal of the eye), may be needed for severe cases or those that are not responsive to other treatments.

What is the prognosis for keratitis?

The cornea does not have blood vessels or other systems that the body normally uses to aid in the healing process, so recovery can be challenging. The prognosis for horses with keratitis depends on the type, the underlying cause, as well as the time to diagnosis and treatment. Prompt, appropriate treatment results in the best prognosis for full recovery. Some cases heal without complications, whereas others require extensive care and are not curable. Severe cases of keratitis can lead to blindness. If left untreated, enucleation may be required.

It is important to involve a veterinarian as early on in a suspected eye injury as possible.

How can keratitis be prevented?

Due to the large size of equine eyes, prominent placement on the head, environments horses typically live in, and their flighty nature as a prey species, there is no definitive way to prevent keratitis or other eye diseases in horses. To minimize the chance for injury, trim plants in pastures to below eye level, do not allow horses to travel with their heads outside trailer windows, and use a fly mask during turnout. Look over your horse for signs of illness or injury at least once a day. If you recognize any of the clinical signs of eye injury or disease, call your veterinarian immediately.

For more information

UC Davis Equine Ophthalmology Service, https://www.vetmed.ucdavis.edu/hospital/large-animal/equine-ophthalmology

*This article may not be reproduced without the written consent of the UC Davis Center for Equine Health. Please email requests to cehadmin@ucdavis.edu.