Effect of Brimonidine and Brimonidine-Timolol on Intraocular Pressure in Normal Equine Eyes (15-09)


Mary Lassaline, DVM, Ph.D., M.A., DACVO
Sara Thomasy, DVM, Ph.D., DACVO           

Glaucoma is a disease characterized by elevated intraocular pressure (IOP) and is a common cause of blindness in horses. Medications such as brimonidine and brimonidine-timolol have been developed to reduce IOP in people with glaucoma by decreasing the amount of fluid within the eye, thereby preserving functional vision and controlling pain associated with this disease. This study investigated the efficacy and safety of two glaucoma drugs, brimonidine and brimonidine-timolol, at lowering intraocular pressure in horses.


The study showed that there were no adverse effects in normal equine eyes treated with brimonidine or brimonidine-timolol. While both medications are well tolerated in normal horses, treatment with these medications did not result in a significant decrease in IOP in the normal horses tested. It is not known whether these drugs would decrease intraocular pressure in horses with glaucoma. It was noted that horses with glaucoma may respond differently than normal horses.

Now that the safety of these two medications has been established, the next step is to test their efficacy in treating the disease in glaucomatous horses. Identifying new ophthalmic medications that successfully lower IOP in horses with glaucoma may decrease the severity of pain and the incidence of blindness in horses with this devastating disease.

This research was reported in the Equine Veterinary Journal.