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Disorders of the Conjunctiva in Horses


Kirk N. Gelatt

, VMD, DACVO, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida

Last full review/revision Apr 2019 | Content last modified May 2019

The conjunctiva is a thin membrane that lines the inside of the eyelids and extends to the cornea of the eye. It plays a role in the movement of tears and the eye, providing protection for the eye from foreign invaders, and healing of the cornea after injury. It is important to identify and treat problems of the conjunctiva, because some can indicate generalized disease, while others can lead to blindness if not treated.

Ruptured blood vessels beneath the conjunctiva may be the result of trauma or a blood disorder. This condition, by itself, does not require treatment, but close inspection is necessary to determine whether more serious changes within the eye have occurred. If definite evidence or history of trauma is not present, then your veterinarian will perform a complete examination to determine the cause of the spontaneous bleeding.

Chemosis is swelling of the conjunctival tissue around the cornea. It occurs to some degree with all cases of inflammation, but the most dramatic examples are seen with trauma, a deficiency of proteins in the blood (hypoproteinemia), allergic reactions, and insect bites. Insect bites are treated with topical corticosteroids and usually heal rapidly. In other cases, specific therapy to treat the original cause is required.

Conjunctivitis (Pink Eye)

Conjunctivitis, also known as pink eye, can occur as a result of many different diseases that affect the eye or even the whole body. The causes vary from infections (including those caused by bacteria, viruses, fungi, and parasites) to environmental irritants. The signs are redness of the eye, swelling of the tissue around the cornea (chemosis, see above), discharge from the eye, and mild eye discomfort. The appearance of the conjunctiva usually is not enough, by itself, to allow your veterinarian to diagnose the cause with only a physical examination. A specific diagnosis often requires a medical history, physical examination, tests on conjunctival scrapings, Schirmer tear test, and occasionally biopsy.

Conjunctivitis in only one eye may result from a foreign object, inflammation of the tear sac (dacryocystitis), or dry eye. Conjunctivitis occurring in both eyes is commonly caused by infection with a virus or bacteria. For example, herpesviruses can produce conjunctivitis in horses. Environmental irritants and allergens are other common causes of conjunctivitis. If a mucus and pus-filled discharge is present, your veterinarian may prescribe a topical antibiotic. However, the antibiotic alone may not bring about healing if other factors are involved. Your veterinarian will also check for foreign objects in the eye, environmental irritants, parasites, and defects of eyelid shape, outline, or form, as these factors also contribute to pink eye. Because conjunctivitis can have multiple causes, your veterinarian may prescribe a combination of treatments.

For More Information

Also see professional content regarding disorders of the conjunctiva in animals.

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