Texas Equine Veterinary Association

www.texasequineva.com • 10 the long-term success is limited due to fibrosis occlusion of the shunt 19–20 . Both trans-scleral cyclophotocoagulation (TSCP) and endocyclophotocoagulation (ECP) reduce aqueous humor production using diode laser energy to ablate the ciliary processes 21–23 . TSCP can be performed in heavily sedated horses. A recent study reported that 59% of horses with a mean follow-up of 49 months remained visual following TSCP 22 . ECP is not routinely performed in horses due to the cost, side effects (cataracts and uveitis), and need for general anesthesia 23 . Medical management is typically required for all patients even after surgery 19–23 . Surgical Procedures for Comfort In Blind Eyes: Surgeries of comfort are indicated for horses that are blind and refractory to medical and/or vision-sparing surgeries. Chemical ciliary body ablation via intravitreal injection of gentamicin can be used to decrease aqueous humor production 1,4 . Intravitreal injection can be performed in sedated horses following topical and local anesthesia 1,4 . Paracentesis is performed prior to injection to reduce IOP 1,4 . Typically, a 22–25 gauge needle is used to injected 50–75 mg of gentamicin sulfate into the posterior segment 1,4 . The needle is positioned 10–12 mm posterior to the dorsolateral limbus and directed toward the optic nerve to avoid lacerating the lens capsule 1,4 . Chronic uveitis, hyphema, and phthisis bulbi are possible sequelae of chemical ablation. Chemical ablation should never be performed in a visual eye. Enucleation is arguably the best option for blind, glaucomatous eyes 4 . Enucleation prevents the risk of future ocular injury and quickly relieves discomfort. Enucleation can be performed either standing or with general anesthesia. Orbital implants may improve the cosmetic outcome after surgery; however, implant rejection and orbital infection has been reported 1,4 . Euqine glaucoma can be a difficult disease to identify and manage. Once identified, prompt treatment of increased intraocular pressure and the underlying cause are critical. Topical therapy is initially the best treatment for glaucoma. Referral to a veterinary ophthalmologist is recommended in all cases of equine glaucoma. WORKS CITED 1. Wilkie DA, Gemensky-Metzler AJ, Lassaline M, Brooks DE. Glaucoma. In: Gilger BC, editor. Equine Ophthalmology. 3 rd edition. Ames, Iowa: Blackwell Publishing; 2017:453-468. 2. Samuelson DA. Ophthalmic anatomy. In: Gelatt KN, editor. Veterinary Ophthalmology. 4 th edition. Ames, Iowa: Blackwell Publishing; 2007:37–148. 3. Samuelson D, Smith P, Brooks D. Morphologic features of the aqueous humor drainage pathways in horses. Am J Vet Res 1989;50:720–727. 4. Tolar EL, Labelle AL. How to Diagnose and Manage Horses with Glaucoma. AAEP Proceedings 2013;59:174-180. 5. Brooks DE, Blocker TL, Samuelson DA, et al. Histomorphometry of the optic nerves of normal horses and horses with glaucoma. Vet Comp Ophthalmol 1995;5:193–210. 6. Cullen CL, Grahn BH. Equine glaucoma: a retrospective study of 13 cases presented at the Western College of Veterinary Medicine from 1992 to 1999. Can Vet J 2000;41:470–480. 7. Latimer CA, Wyman M. Neonatal ophthalmology. Vet Clin North Am Equine Pract 1985;1:235–259 8. Davidson HJ, Blanchard GL, Wheeler CA, et al. Anterior uveal melanoma, with secondary keratitis, cataract, and glaucoma, in a horse. J Am Vet Med Assoc 1991;199:1049–1050. 9. van der Woerdt A, Gilger BC, Wilkie DA, et al. Effect of auriculopalpebral nerve block and intravenous administration of xylazine on intraocular pressure and corneal thickness in horses. Am J Vet Res 1995;56:155–158. 10. Knollinger AM, La Croix NC, Barrett PM, et al. Evaluation of a rebound tonometer for measuring intraocular pressure in dogs and horses. J Am Vet Med Assoc 2005;227:244–248 11. Dziezyc J, Millichamp NJ, Smith WB. Comparison of applanation tonometers in dogs and horses. J Am Vet Med Assoc 1992;201:430–433 12. Komaromy AM, Garg CD, Ying GS, et al. Effect of head position on intraocular pressure in horses. Am J Vet Res 2006;67:1232–1235. 13. Herring IP, Pickett JP, Champagne ES, et al. Effect of topical 1% atropine sulfate on intraocular pressure in normal horses. Vet Ophthalmol 2000;3:139–143. 14. Mughannam AJ, Buyukmihci NC, Kass PH. Effect of topical atropine on intraocular pressure and pupil diameter in the normal horse eye. Vet Ophthalmol 1999;2:213–215. 15. Van Der Woerdt A, Wilkie DA, Gilger BC, et al. Effect of single- and multiple-dose 0.5% timolol maleate on intraocular pressure and pupil size in female horses. Vet Ophthalmol 2000;3:165–168. 16. Willis AM, Robbin TE, Hoshaw-Woodard S, et al. Effect of topical administration of 2% dorzlamide hydrochloride or 2% dorzlamide hydrochloride-0.5% timolol maleate on intraocular pressure in clinically normal horses. Am J Vet Res 2001; 62:709– 713. 17. Willis AM, Diehl KA, Hoshaw-Woodard S, et al. Effects of topical administration of 0.005% latanoprost solution on eyes of clinically normal horses. Am J Vet Res 2001;62:1945– 1951. 18. Tofflemire K, Whitley EM, Allbaugh R, et al. Effect of topical ophthalmic latanoprost 0.005% solution alone and in combination with diclofenac 0.1% solution in healthy horses: a pilot study. Veterinary Ophthalmology 2017;20,398-404. 19. Townsend WM, Langohr IM, Mouney MC. Feasibility of aqueous shunts as therapy for equine glaucoma. International Equine Ophthalmology Consortium. Sterling, Scotland. 2012. 20. Wilson R, Dees DD, Wagner L et al. Use of a Baerveldt gonioimplant for secondary glaucoma in a horse. Equine Veterinary Education 2015; 27: 346-351. 21. Miller TL, Willis AM, Wilkie DA, et al. Description of ciliary body anatomy and identification of sites for transscleral cyclophotocoagulation in the equine eye. Vet Ophthalmology 2001;4:183–190 22. Annear MJ, Wilkie DA, Gemensky-Metzler AJ. Semiconductor diode laser transscleral cyclophotocoagulation for the treatment of glaucoma in horses: a retrospective study of 42 eyes. Vet Ophthalmology 2010;13:204–209. 23. Harrington JT, McMullen RJ Jr, Cullen JM, et al. Clinical and histopathologic effects of diode laser endoscopic cyclophotocoagulation in the normal equine eye. American College of Veterinary Ophthalmologists, 42nd Annual Conference. Hilton Head, SC. 2011:100.

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