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Objective: To investigate the effects of topical dorzolamide 2% q8h and brinzolamide 1% q8h, administered either alone (A and B, respectively) or in combination with topical timolol 0.5% q12h (C and D, respectively), on the circadian pattern of intraocular pressure (IOP), the pupil size, and heart rate in healthy cats. Methods: In this prospective, randomized, double‐blinded study, 10 healthy, adult cats were randomly assigned to one of four groups and the eye to be medicated was randomly assigned. IOP, pupil diameter, and heart rate were measured at 3‐hour intervals. A 5 days' adjustment period was followed by a 5 days' placebo (baseline) period. Then, all groups of cats received all four treatments (A‐D) according to a Latin square‐based rotating schedule. Five days' medication periods were alternated with 3 days' washout periods. Results: Mean baseline IOP was 13.6 ± 2.7 mm Hg. All treatments resulted in a statistically significant decrease in mean IOP in the treated eye: A: −2.33 mm Hg (95% CI: −2.71, −1.94), B: −1.91 mm Hg (95% CI: −2.30, −1.53), C: −2.36 mm Hg (95% CI: −2.74, −1.97), and D: −2.37 mm Hg (95% CI: −2.76, −1.98) and the nontreated eye: A: −0.19 mm Hg (95% CI: −0.28, −0.11), B: −0.18 mm Hg (95% CI: −0.27, −0.10), C −0.31 mm Hg (95% CI: −0.40, −0.23), and D: −0.24 mm Hg (95% CI: −0.32, −0.15). Timolol resulted in an additional, significant decrease in IOP of 4% and 5%, respectively, compared to A and B, and in mild bradycardia and miosis. Conclusions: Topical administration of dorzolamide 2% and brinzolamide 1% q8h significantly decreased IOP in healthy cats. Supplemental timolol 0.5% eye drops q12h resulted in an additional, statistically significant reduction of IOP. [ABSTRACT FROM AUTHOR]