Dorzolamide–timolol combination and retinal vessel oxygen saturation in patients with glaucoma or ocular hypertension

Aims:To examine whether the addition of dorzolamide to timolol monotherapy influences oxygen saturation in the human retina.Methods:Non-invasive spectrophotometric retinal oximetry was used to measure oxygen saturation in retinal vessels. Twenty patients with open-angle glaucoma (11) and ocular hypertension (9) were recruited. The patients were randomised into receiving timolol monotherapy or dorzolamide–timolol combination for an 8-month test period, followed by a second test period, before which the patients switched treatments. Oximetry measurements were performed at 2-month intervals during each period. Of the 20 patients, 13 followed the study protocol into the second test period, and 10 managed all study visits.Results:The oxygen saturation in retinal vessels was stable within the test periods. The mean arteriolar saturation was 96 (2)% (mean (SD)) during timolol monotherapy and 97 (2)% during dorzolamide–timolol combination therapy (p = 0.17, all patients pooled, n = 13). Corresponding values in venules were 66 (5)% during timolol monotherapy and 65 (6)% during dorzolamide–timolol therapy (p = 0.13). Patients who started on dorzolamide–timolol combination showed a significant reduction in arteriolar (98 (2)% to 95 (2)%, p