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Effects of 0.2% brimonidine and 0.2% brimonidine–0.5% timolol on intraocular pressure and pupil size in normal equine eyes
Author(s) -
Von Zup M.,
Lassaline M.,
Kass P. H.,
Miller P. E.,
Thomasy S. M.
Publication year - 2017
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/evj.12695
Subject(s) - brimonidine , timolol , ophthalmology , medicine , intraocular pressure , ocular hypertension , glaucoma , anesthesia
Summary Background Brimonidine is an α 2 ‐adrenergic agonist that decreases aqueous humour production and may increase uveoscleral outflow. It has not been evaluated in normal or glaucomatous equine eyes. Objectives To evaluate the efficacy and safety of brimonidine in lowering intraocular pressure ( IOP ), alone and in conjunction with timolol, as a treatment for equine glaucoma by comparing IOP in normal equine eyes treated with brimonidine and brimonidine–timolol, respectively, with IOP in control eyes. Study design A balanced crossover design with 16 horses receiving one of two treatments, brimonidine and brimonidine–timolol, during each of two 10‐day study phases, was used. Four horses were randomly assigned to each of four combinations of treated eye (right or left) and drug order within the two 10‐day study phases (brimonidine first or brimonidine–timolol first). Methods Pupil size and conjunctival hyperaemia were assessed twice per day and IOP was measured three times per day using rebound tonometry in both eyes of 16 normal horses throughout two 10‐day study periods (brimonidine and brimonidine–timolol) separated by an 18‐day washout period. One eye of each horse was treated with brimonidine or brimonidine–timolol and the opposite eye was treated with balanced salt solution ( BSS ). Results There were no adverse effects and no significant changes in pupil size in normal equine eyes treated with brimonidine or brimonidine–timolol. Average IOP in normal equine eyes treated with brimonidine (25.6 mmHg) was statistically higher than in eyes treated with brimonidine–timolol (24.6 mmHg) or BSS (24.5 mmHg). However, IOP differences were of ≤1 mmHg and thus not clinically important. Main limitations Horses with normal eyes may not be as sensitive to the IOP ‐lowering effects of treatment as horses with glaucoma. Conclusions Brimonidine and brimonidine–timolol are well tolerated in normal horses but do not decrease IOP .