Corneal ulcers in horses

Corneal ulcers account for the majority of ophthalmological consultations in horses. Generally of traumatic origin, they usually have a good prognosis, but require appropriate treatment and rigorous follow-up.

1. What is an ulcer and how is it diagnosed?

The eyeball is made up of two parts: the sclera (white part of the eye) and the visual part. The visual part is protected by an envelope called the cornea.

In horses, the sclera is barely visible, so the cornea covers almost the entire accessible part of the eye, even when the eyelids are wide open.

An ulcer is an erosion of the cornea, in the same way as a wound on the skin. The wound analogy makes it clear that an ulcer, like any wound :

- is mostly traumatic, although some viral keratitis can cause ulcers.

- can be more or less deep

Symptoms are fairly uncharacteristic: the eye is generally closed, painful and has a more or less thick discharge.

Diagnosis, however, is not as straightforward as for a cutaneous wound. As the cornea is transparent, superficial lesions are not always easy to identify. In this case, the veterinarian uses a dye, fluorescein, which only binds to superficial lesions on the cornea. The ulcer then appears fluorescent green on the eye.

2. What treatments are available?

As we've seen, an ulcer is the equivalent of a wound, so the veterinarian will seek to improve and accelerate healing.

The main problems encountered are frequent infection of the cornea, associated with intense pain and itching that can aggravate the ulcer.

The most common treatment consists in administering antibiotic and healing eye drops to the horse. Atropine is also prescribed to dilate the pupil and limit pain and after-effects. Frequency of administration is generally the key to success, but this can prove difficult depending on the horse's cooperation and the owners' availability.

For horses that really don't respond to local treatment, the vet may fit a sub-palpebral catheter. This small, flexible tube, attached to the horse's mane, ends up under the eyelid, allowing frequent injection of eye drops without having to approach or open the eye.

Local treatment is usually combined with systemic anti-inflammatory drugs to manage pain.

In some cases, medical treatment can fail, if the bacteria escape antibiotics or if the cornea is atonic, i.e. it doesn't heal.

In this case, the first step may be to intervene under tranquilization and local anesthetic to debride the ulcer. The vet will remove the cornea from the edges of the ulcer if they are detached, which limits the diffusion of eye drops. He may also scarify the cornea to stimulate healing.

When the ulcer is too deep or does not respond to previous treatments, the best option is surgery.

The cornea doesn't sew as well as the skin, because it's fragile and tears more easily. Surgery therefore involves what is known as conjunctival grafting. The surgeon uses a small flap of connective tissue (inside the eyelid), which is attached to the cornea to completely cover the ulcer. This helps to protect the cornea and improve its vascularization for proper healing. Once the eye has healed, the part attaching the flap to the eyelid can be cut away, allowing the connective tissue to regress and disappear.

In the case of perforating ulcers, i.e. when the entire thickness of the cornea is affected, known as "punctured eye", only very early surgery can save the eye, provided the lesion is small.

3. What happens next? After-effects and consequences

Most ulcers have a good prognosis and leave no after-effects.

However, especially in the case of deep lesions, the horse may retain a scar. This takes the form of a white trace on the cornea. It doesn't bother the horse unless it's very large. The discomfort caused can be compared to that of dirt on a spectacle lens.

A relatively frequent complication is uveitis secondary to the ulcer. Even if the attack is managed while the ulcer heals, the eye may subsequently become sensitive and prone to recurrent uveitis.

To avoid ulcers, a semi-rigid protective mask is highly recommended. This prevents trauma caused by a branch or spikelet under the eyelid, for example.

Pauline Cantet, equine veterinarian.