Description

The cornea is the transparent surface of the front of the eyeball and is prone to injury in the daily activities of most horses. Corneal ulcers are usually caused either by injury or by fungi. Corneal injuries can quickly become severe turning into corneal ulcers which may threaten the vision of the horse.

The outer layer of the cornea is known as the epithelial layer. Next is the stroma, and beneath the stroma is the descemel's membrane. Injuries that involve only the outer layer are considered to be abrasions. Injuries that involve the stroma are ulcers.

Many ulcers can be seen by the naked eye, but if a corneal ulcer is suspected but can't be seen, staining the area with fluorescein, an orange dye that becomes fluorescent green and binds to the surface where the epithelial layer has been damaged, will help determine whether or not there is an ulcer and the extent of the damage.

Once a cornea is injured, it is susceptible to infection from both bacteria and fungi. Some of these bacteria produce enzymes that destroy the substance of the stroma, leading to large, rapidly deteriorating ulcers. If not treated promptly, they may lead to a rupture of the eyeball. .

In the case of fungi, chronic inflammation of the cornea known as keratitis can severely affect vision and abscesses may develop in the stroma, sealing in bacteria, fungi, or foreign matter as the epithelial cells divide and migrate over the ulcer.

Symptoms

• Tight squinting, as if in pain
• Reddened conjunctiva around the eye
• Avoidance of bright light
• Excess tear production and discharge

Causes

A swishing tail, branches of vegetation, and debris kicked up on a dusty trail or racetrack and many other situations may result in scratchs or injuries to the cornea of the horse's eye.

Foreign particles of dirt, grit, sand, hay, or wood that enter the eye may cause injury to the cornea by becoming imbedded or scratching the transparent surface of the front of the eyeball. Both bacteria and fungi in the environment may enter the smallest scratch or cut in the cornea, leading to ulcers that can threaten vision and, in some cases, cause the loss of the eye if aggressive treatment is not undertaken quickly and effectively.

At the first symptoms, a veterinarian with a background in ophthalmology should be brought in to diagnose and treat the problem.

Prevention

While it is essentially impossible to remove all risk of corneal injury, regular observation of the eyes will allow a horse owner to prevent particles from causing extensive damage. Uncomplicated superficial abrasions will heal quickly with minimal treatment. If the cornea develops ulcer-like symptoms, a prompt diagnosis by a veterinarian and appropriate treatment will ensure minimum damage to the eye.

Treatment

If a corneal ulcer is suspected, examination and treatment should begin within 24 hours to prevent further injury and infection and to ensure healing within a few days. The horse should be kept in a darkened stable or wear a pacifier with the affected eye taped over, since bright light is extremely painful.

Treatment should be aimed at preventing infection, reducing inflammation, and keeping the pupil of the eye dilated. One of the first steps is to make sure that all foreign material, such as dirt, sand, grit, and pieces of hay or wood are removed from the eye. If the eye is inflamed, use of a systemic anti-inflammatory, such as flunixin, is important to provide pain relief and decrease or prevent inflammation.

Broad-spectrum, topical antibiotics should be used to prevent bacteria from infecting the ulcers and preventing healing. Atropine will dilate the pupil, allow normal drainage, and will help to prevent and control uveitis. In severe cases when the ulcers are deep, it may be necessary to cut and scrape away unhealthy tissue under local or general anesthesia.

Because many horses resist repeated treatments, it is sometimes necessary to use a lavage system through the nasolacrimal duct or the upper eyelid that allows drops of medication to be applied regularly without having to handle the eye.

If the corneal ulcer is the result of a fungal infection, a corneal graft may be required. Any ulcer that is not responsive to antibiotic therapy or that exhibits a white plaque appearance should be checked for fungi by a competent veterinarian with a background in ophthalmology.

Deep ulcers may take weeks to heal since there is no direct blood supply to provide nutrition to the cells. Sometimes it becomes necessary to take a section of the fleshy conjunctiva from around the eyeball and suture it over the ulcer, providing for circulation of blood and protection during the healing process.