IntroductionGlaucoma is an irreversible chronic eye disease in which intraocular pressure (IOP) control is important. This study aimed to assess the IOP-lowering effects and adherence scores between fixed combination dorzolamide/timolol maleate (FCDT) and non-fixed combination dorzolamide and timolol XE (NFDT) in open-angle glaucoma (OAG) patients.MethodsA randomised controlled trial in a parallel, single-blinded study involving 60 OAG patients was conducted. The patients were randomised into FCDT or NFDT based on a block randomisation technique. A pre-study run-in with Gutt timolol was administered for two weeks. IOP was assessed at baseline, month 1 and month 3, with a bottle weight measurement at month 3.ResultsOnly 55 OAG patients were analysed, with 8.4% dropping out. A statistically significant mean IOP reduction was observed in each group from baseline to month 1 (FCDT: mean difference [MD] = 4.93, 95% confidence interval [CI] = 4.00, 5.86); NFDT: MD = 4.92, 95% CI = 4.024, 5.82) and from baseline to month 3 (FCDT: MD 5.17, 95% CI = 4.19, 6.15; NFDT: MD = 4.85, 95% CI = 3.874, 5.82). The overall FCDT mean IOP was significantly lower by 1.02 mmHg (95% CI = −2.01, −0.02) than NFDT (F(1, 53) = 4.19;P= 0.046). A significant interaction was observed between time and treatment at month 3, with the mean IOP for FCDT being lower by 1.22 mg than for NFDT (P= 0.037). The mean adherence score was significantly higher in the FCDT group than in the NFDT group (tstat (df) = 3.88 (53);P< 0.001). The reduction in IOP between the groups became non-significant after adherence was adjusted (F(1, 52) = 2.45;P= 0.124).ConclusionBoth drugs showed a decrease in IOP but more so in FCDT. However, no difference was found in terms of medication adherence. An emphasis on treatment compliance is needed.