Double-masked three-period crossover investigation of timolol in control of raised intraocular pressure

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Abstract
Forty patients with an intraocular pressure (IOP) between 30 and 49 mmHg in either eye (57 eyes) were recruited into a trial of timolol 0.25% versus timolol 0.5%. Patients were randomised to receive the two concentrations of drug in the order ABA or BAB. The study period was 12 weeks for each patient, with changes in drug concentration at 4 and 8 weeks. IOPs were measured at the same time every 2 weeks. Mean IOP of both eyes was used, excluding any eyes with initial IOPs of less than 30 mmHg. There was no difference between the 2-week and 4-week pressure readings, which were therefore combined. There was no statistically significant difference in the initial IOPs of the two groups (0.5%, 33.45 mmHg; 0.25%, 32.63 mmHg) nor in the initial fall in IOP with either concentration (0.5%, 12.03 mmHg; 0.25%, 11.31 mmHg). Furthermore, changing from one concentration to the other had no significant effect on IOP. Mean IOPs over the whole study period averaged 21.12 mmHg for timolol 0.25% and 20.75 mmHg for timolol 0.5%. Again these differences were not statistically significant. The statistical power of the study was estimated to exceed 85%. The authors suggest that there is no justification for use of the 0.5% strength, which is more expensive and has no advantages.