Dorzolamide-Timolol Combination and Retinal Vessel Oxygen Saturation in Patients With Glaucoma or Ocular Hypertension

Abstract

Purpose: : 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 the oxygen saturation in retinal arterioles and venules in patients on dorzolamide-timolol combination therapy or timolol monotherapy. A total of 20 patients with open angle glaucoma (11) and ocular hypertension (9) were recruited. In a randomized, double-blind cross-over design, the patients were randomised into receiving timolol monotherapy or dorzolamide-timolol combination for an 8 month test period, followed by a second test period, during which the patients received the other treatment. Oximetry measurements were performed 4 times (2 month intervals) in each period. Of the 20 patients, 13 completed the study to provide two measurements in each test period.

Results: : The oxygen saturation in retinal arterioles and venules was stable within the test periods. 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<0.01) and venular saturation (69±5% to 66±6%, p<0.05) when changing to timolol monotherapy. No significant changes were noted in patients who started on timolol and changed to dorzolamide-timolol combination.

Conclusions: : Adding dorzolamide to timolol monotherapy has minimal effect but going from dorzolamide-timolol combination to timolol alone lowered arteriolar and venular oxygen saturation. The retinal oxygen saturation measurements show high degree of stability over an extended period of time. Previous studies have suggested increased retinal and optic nerve blood flow with dorzolamide. Unchanged oxygen saturation and increased blood flow would indicate increased oxygen delivery to the retina.

Keywords: retina • oxygen • carbonic anhydrase