The effect of topically applied dorzolamide on intra-ocular pressure in healthy adult cats
Gee, R. de
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Objective: to investigate if dorzolamide 2% eye drops significantly lower intraocular pressure (IOP) in healthy adult cats. Animals: nine 18-19 and one 12-month-old European shorthair cats (5 castrated males, 5 spayed females). All were healthy but one male cat which, during the study, was diagnosed with a mitral valve insufficiency. Procedure: IOP, pupil diameter and heart rate were assessed with a rebound tonometer, digital callipers and stethoscope, respectively. All measurements were executed at 3-h intervals over 24-h periods spanning 42 days. These periods were divided into an adjustment phase (days 1-6), placebo phase (days 7-13) and treatment phase (days 14-42). Cats were divided into four groups (Random Team Generator). The first five days of the adjustment phase were used to get cats as well as their examiners accustomed to the procedures, and were followed by a day of rest. The placebo phase lasted five days followed by two days of rest. Then, five-day treatment periods were alternated with three-day washout periods. Apart from dorzolamide, three other kinds of medication (brinzolamide, dorzolamide with timolol and brinzolamide with timolol) were administered to the cats. These other kinds of medication are discussed in other papers. Each group of cats was rotated to a different kind of medication every eight days (Latin square). By the end of the study all cats had received all medications. Results: A circadian rhythm in IOP during the adjustment and placebo phases was found as IOP was significantly different at 18:00, 21:00, 0:00, 3:00 and 6:00 in comparison with 9:00. IOP following treatment with dorzolamide was significantly lower than following the placebo at all time points, and the variance between highest and lowest IOP during the day was smaller during the treatment phase. IOP in the untreated eye was not significantly different from the treated eye in the placebo and treatment phases. Pupil diameter and heart rate were not influenced by treatment with dorzolamide. Conclusion: During treatment with dorzolamide, the daily fluctuations in IOP were less pronounced than during treatment with the placebo. Topical 2% dorzolamide significantly lowered IOP in healthy adult cats. Future research into dorzolamide as a possible treatment for glaucoma in cats is warranted.