The current study examined the effects of timolol-dorzolamide fixed combination (TDFC) or latanoprost 0.005% on 24-hour systolic blood pressure (SBP), diastolic blood pressure (DBP) and diastolic ocular perfusion pressure (DOPP) in newly diagnosed primary open-angle glaucoma patients. DOPP is calculated by subtracting IOP from DBP, and levels below 50 mm Hg have been shown to be a risk factor for glaucoma progression. Medications used to treat glaucoma, which also lower blood pressure, may adversely affect DOPP. Therefore glaucoma patients who take anti-hypertensive medication may be at risk for the progression of glaucomatous damage if their DOPP drops below 50 mm Hg.
Subjects in the study were 27 previously untreated glaucoma patients older than 45 years without histories of cardiovascular disease and who had not undergone eye surgery or laser treatment and were not taking anti-hypertensive medication. Twenty-four-hour assessment, which in this study involved IOP measurement every two hours and more frequent blood pressure measurement, was chosen in order to avoid variations in readings that can occur when they are taken only once during the day or night. After 24-hour base line readings, each patient was randomly placed on either once-daily latanoprost or twice-daily TDFC for six weeks. Following a four-week washout period, patients switched medications and underwent a second series of base line measurements. At the end of the six-week period for each medication, 24-hour measurements of SBP, DBP and IOP were taken.
Both TDFC and latanoprost each caused a significant decrease in IOP, although TDFC was more effective. TDFC also decreased SBP and DBP but latanoprost did not. Both treatments significantly increased DOPP, latanoprost by lowering IOP. Although TDFC lowered DBP, this was offset by its greater IOP-lowering effects compared with latanoprost, with the end result being DOPP enhancement.
This study points out that since a low DOPP level is an important risk factor for glaucoma progression, anti-glaucoma medication should attempt to raise DOPP and not lower it. However, drops in DOPP can occur with medications containing antihypertensive components that are unable to lower IOP enough to offset their blood pressure-lowering effects. Lowering blood pressure in glaucoma patients requires adequate lowering of IOP in order to maintain sufficient DOPP levels.
Dr. Freedman is a consultant to Optonol, Ltd., and IOP, Inc.