Conjunctivitis, colloquially known as pinkeye, results from a variety of causes in horses. It occurs when the lining of the eyelids becomes inflamed. One or both eyes may be affected. If it appears in both eyes, suspect a viral or bacterial infection. An allergen also could be the culprit.
If your horse experiences any eye issues, call your veterinarian immediately. Eye problems are always a veterinary emergency, as conditions can deteriorate quickly. While pinkeye usually resolves promptly with treatment, it's important for your vet to make an accurate diagnosis, since conjunctivitis and some more serious eye problems share some of the same symptoms. Conjunctivitis can be a sign of an underlying eye disease, including uveitis, glaucoma or corneal ulcers. These ocular disorders, which can cost your horse his vision, more often occur in one eye.
In addition to a pink eye, symptoms of equine conjunctivitis include a watery or mucousy discharge, swollen or irritated eyelids, light avoidance and eye rubbing. Conjunctivitis is somewhat painful, but not usually severely so.
Diagnosing and Treating Conjunctivitis
Your vet will examine your horse's eye, making sure no foreign items or anatomical eyelid abnormalities are responsible for the redness and swelling. If that's not an issue, and your vet sees no evidence of more serious eye disease, she likely will prescribe topical antibiotics to treat conjunctivitis. Generally, conjunctivitis clears up within a week if the antibiotic ointment is placed in the eye two or more times daily. Your vet might recommend placing a fly mask over your horse's eyes both to keep insects away and to protect the eye from dust and other irritants while healing. If the pinkeye does not clear up, or if your vet suspects that your horse is suffering from more than ordinary conjunctivitis, she may conduct a conjunctival scraping or other tests to determine the cause. More extensive treatment is based on test results.