Texas Equine Veterinary Association

require topical anesthesia as they measure the force required to flatten the corneal surface 11 . Furthermore, applanation tonometers require a latex cover to protect the tip of the device 11 . These tips should be changed between each patient and sometimes between eyes to prevent contamination. The mean intraocular pressure with Tono-Pen is 21 ± 5.9 mmHg (range 9-33 mmHg) 11 . Digital palpation of the globe may provide a qualitative assessment of eye pressure; however, this method is insufficient for accurate diagnosis and monitoring of glaucoma. Treatment: The goal of glaucoma therapy is to maintain IOP under a threshold that damages the optic nerve and retina. The ideal intraocular pressure is unknown; however, most clinicians agree that < 25 mmHg is optimal 4 . All glaucoma treatments attempt to reduce aqueous humor production and/or increase aqueous drainage. The underlying cause of glaucoma, if known should also be addressed and treated. For patients with equine recurrent uveitis this may include topical and/or oral anti-inflammatory treatments 1,4 . The use of atropine in horses with glaucoma secondary to ERU is controversial 13-14 . Atropine may increase intraocular pressure; therefore, atropine should be used with caution and in conjunction with close monitoring 13–14 . Medical therapy for glaucoma is considered the first line of therapy. Drug classes that reduce aqueous humor production include beta- adrenergic antagonists (beta-blockers) and carbonic anhydrase inhibitors (CAIs). Beta-blockers inhibit cAMP activity in the ciliary body to decrease aqueous production. Timolol maleate 0.5% is the most commonly used topical beta-blocker 15 . Timolol 0.5% is able to reduce IOP in normal horses and topical treatment every 8–12 hours is recommended 15 . CAIs inhibit carbonic anhydrase, an enzyme in the ciliary body epithelium needed for aqueous humor production 16 . Commercially available products include brinzolamide 1% and dorzolamide 2% 16 . Both appear to be effective in reducing IOP in normal horses. Dorzolamide is used more frequently in the United States because it is more cost effective. A combination product of dorzolamide 2% and timolol 0.5% is also available 16 . Topical CAIs should be given every 8–12 hours 16 . Prostaglandin analogues are capable of increasing aqueous outflow in many species 17–18 . Topical prostaglandin analogues include latanoprost 0.005% and travaprost 0.004% 17 . In healthy horses, topical latanoprost 0.005% decreased IOP 18 . The IOP lowering effects of latanoprost in normal horses, however, was less than other hypotensive medications and common side effects included squinting, tearing, conjunctival hyperemia, and miosis 18 . Due to the relatively minor hypotensive effect and risk of adverse effects, the author suggests prostaglandin analogues not be used as a first line of therapy for horses with glaucoma 18 . Surgical treatments to maintain vision: Surgical options for increasing aqueous humor outflow utilize implants such as valved (Ahmed) or non-valved (Baerveldt) shunts 19–20 . These procedures require general anesthesia and Photo credit to Dr. Ellison Bentley, DVM, DACVO Figure 2: 5-year-old Quarter Horse gelding with glaucoma.

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