Sub-Tenon's anesthesia in equine cataract surgery and vitrectomy: a retrospective case series (2018-2022)

A retrospective data analysis was performed on 17 eyes from 13 horses which underwent a sub-Tenon's injection to facilitate phacoemulsification or pars plana vitrectomy under general anesthesia between 2018 and 2022. All procedures were performed by the same veterinary ophthalmologist. Seven eyes received a sub-Tenon's dose of 7 ml lidocaine (XylocainÒ, 2 % lidocaine hydrochloride, Germany, Aspen Germany GmbH), and 10 eyes received 7 ml mepivacaine (MepinaestÒ purum 2 %, mepivacaine hydrochloride, Switzerland, Gebro Pharma GmbH). Statistical analysis compared onset and duration of globe centralization and pupil mydriasis between the two groups. Intraoperative and postoperative complications were also assessed. Mepivacaine had a significantly later onset of action regarding globe centration and mydriasis (8,9 minutes vs. 6 minutes), but also a significantly longer duration of globe centration than lidocaine (31,5 minutes vs. 15,6 minutes). There were no statistically relevant differences between solutions regarding duration of pupil dilation (40,4 minutes for 2 % lidocaine vs. 69,2 minutes for 2 % mepivacaine). Chemosis occurred in all 17 eyes. Surgical complications included corneal epithelial defects (5), retinal detachment (5), lens opacification (5), temporary blindness during recovery (3) and glaucoma (2). Sub-Tenon's anesthesia is a feasible alternative to systemic neuromuscular blockade and retrobulbar block anesthesia for surgical procedures on the equine globe. A controlled prospective in vivo study is needed to further evaluate effects and risks.