"Glaucoma (increased fluid pressure within the eye to a level incompatible with eye health) in horses is not well recognized, but look for it in cases of cloudy cornea, corneal edema, or severe unrelenting ocular inflammation," said Brian Gilger, DVM, MS, Dipl. ACVO, of North Carolina State University, during his presentation on diagnosing and treating glaucoma at the 2003 American Association of Equine Practitioners convention.

Aqueous humor, or the fluid that fills the eye, is constantly produced. Glaucoma is caused by decreased outflow of this fluid from the equine eye, he said. This could be due to an abnormally developed, damaged, or obstructed drain.

Gilger said because of differences in glaucoma signs between horses, dogs, or humans, and the different type of tonometer required to evaluate intraocular pressure in the horse, "Glaucoma is not commonly recognized and therefore frequently not treated appropriately in many horses."

"The most common cause of glaucoma in horses is chronic or recurrent uveitis (a type of secondary glaucoma)," he said. "These horses have multiple episodes of intraocular (within the eye) inflammation followed by a severe unrelenting bout of ocular cloudiness and discomfort (as a result of the development of glaucoma) that does not respond to traditional uveitis therapy. In general, the horse tends to lose vision much later in the disease process compared with dogs and humans