Of all the domestic species, it seems to me that the horse is the most sensitive to diseases of the outer layer of the eyeball called the cornea. Dogs and cats commonly get severe injuries to the cornea from scratches, and in general these lesions seem to heal well. Cattle have major infections with pink eye and although some vision may be lost, they rarely lose the eye. However, a tiny scratch that causes a corneal ulcer on a horse's eye can lead to blindness and possibly require removal of the eye. For this reason, it is imperative that anytime a horse is squinting an eye, call a veterinarian immediately.

You should not use any mediation in the horse's eye until it is examined by a vet. Many of the opthalmic medications commonly used in small animals contain cortisone and cortisone can make the horse's eye susceptible to infection, especially a fungal infection. Also, the incorrect use of antibiotics in a horse's eye can increase the risk of fungal infections; fungal infections are common in horses and can lead to loss of the eye.

Scrapings and cultures of the corneal ulcer are required to make a diagnosis. Any infection of the equine cornea is potentially serious and usually requires treatment every 4 to 6 hours, which can be a difficult problem. The eye must be dilated to prevent internal damage and relieve pain. Treatment with topical antifungal and antibiotics is required until the ulcer is healed. Sometimes, a tube system must be inserted in the eye to allow frequent treatment as many horses greatly object to treatment. If a horse's corneal ulcer does not heal in a week, it should be considered infected and different treatment may be required.