One important strategy for addressing ophthalmic injury from ocular trauma or corneal ulcers is to control pain and inflammation. Commonly used medications for this purpose include NSAIDs such as flunixin meglumine and phenylbutazone. Besides the use of NSAIDs, previous studies have identified that acupuncture reduces intraocular pressure in addition to providing analgesia in horses with equine recurrent uveitis.
A Hungarian study sought to create an ophthalmic pain scale while also comparing various treatments that provide at least a 48-hour analgesic effect [Makra, Z.; Csereklye, N.; Riera, M.M.; et al. Effects of Flunixin meglumine, Phenylbutazone, and Acupunture on Ocular Pain Scores in the Horse: A Pilot Study. Journal of Equine Veterinary Science 98 (2021) 103375 doi.org/10.1016/j.jevs.2021.103375].
Four horses aged 6-9 years with normal eyes were used in the study. A 6-mm disc of corneal epithelium and its basement membrane were manually removed. This procedure was alternated between the left and right eyes of each horse at four-week intervals for four times. Each session, the horse was treated four hours after wounding with either a) flunixin meglumine (1.1 mg/kg) twice daily; b) phenylbutazone (4.4 mg/kg) once daily; c) 20 minutes of targeted electroacupuncture once daily; or d) served as a control with saline injection IV every 24 hours. Topical hyaluronic acid was applied every eight hours in every situation. Treatments continued until healing; all wounds healed to a point of no flourescein uptake by five days, on average.
Pain scoring was evaluated by heart rate, corneal touch threshold to elicit a blink reflex, six ocular signs and three behaviors (comfort, appetite, head rubbing). Scores were assessed at time 0 before wounding, and then at 4, 6, 8 and 10 hours post-op, then every four hours for the first two days. The ocular signs scored included blepharospasm (abnormal contraction of the eyelid muscles), tearing, eyelid swelling, corneal opacity, conjunctival hyperemia or chemosis. Blepharospasm was the most consistent pain indicator. The peak of ocular pain occurred within 2-3 days following wounding.
The only significant difference between the treatment groups compared to the placebo control was achieved with flunixin meglumine treatment over the initial 46 hours. The researchers concluded that flunixin meglumine is more reliable in managing corneal pain compared to phenylbutazone or electroacupuncture.