Glaucoma is a disease associated with elevated pressure within the eye. Symptoms include cloudy cornea, dilated pupils, enlarged eyeball and inflammation of the iris. If left untreated, glaucoma leads to retina and optic nerve damage and blindness. The equine eye gets its nutrition from fluids that run through special pathways in and out. Obstruction of this outflow of fluid can be the result of an abnormally developed drain (i.e., primary glaucoma) or through damage to the drain from scarring, or accumulation of debris (i.e., secondary glaucoma). The result of this obstruction is retention of fluids and increase in the pressure within the eye. The most common cause of glaucoma in horses is chronic or recurrent uveitis. Primary glaucoma usually affects both eyes, therefore the unaffected eye usually requires preventive therapy. Secondary glaucoma may not affect both eyes unless the horse has recurrent uveitis in both eyes.
Signs include inflammation of the iris, tumors, cataracts, cornea swollen with an excessive accumulation of fluid. At the advanced stages of the disease, the size of the eyeball may increase and eye lenses may dislocate. Equine practitioners usually consider glaucoma as the cause of any unexplained corneal edema or ocular cloudiness and in cases of severe unrelenting ocular inflammation. Accurate measurement with a portable tonometer is essential to make the definitive diagnosis and to monitor the response to therapy. Treatment consists in reducing the inflammation using anti-inflammatory medications, decreasing the production of fluids or laser therapy.