Topical carbonic anhydrase inhibitors and visual function in glaucoma and ocular hypertension

Background: Dorzolamide and brinzolamide are topical carbonic anhydrase inhibitors (CAI) indicated for patients with glaucoma and ocular hypertension. Scope: An evidence-based review of clinical trials of dorzolamide and brinzolamide was undertaken to determine an effect of these medications on visual function (primarily visual field) in open-angle glaucoma and ocular hypertension. Using the keywords 'dorzolamide' and 'brinzolamide', all articles describing trials of these medications reporting on visual acuity, contrast sensitivity and visual field from September 1966 to July 2009 were found in MEDLINE and EMBASE databases. No information from other sources was included in this review. Findings: A relatively modest number of trials was identified, where impact of therapy on one or more of the visual function modes was reported. In the studies of less than 1 year duration (3 days to 1 year, 23 studies) in all but three studies treatment with topical CAIs did not influence visual function, in two studies with dorzolamide some improvement in the contrast sensitivity was observed and in one open-label retrospective no-control-group study with dorzolamide visual field indices improved significantly. A different picture was seen in long-term studies, which were designed and powered to detect changes in visual field. One large study (European Glaucoma Prevention Study) with dorzolamide versus placebo failed to detect significant protective effect of the drug on glaucoma occurrence in ocular hypertensives. Several interesting aspects of this study are discussed in detail. The other two long-term studies reported on the superiority of adding dorzolamide over timolol therapy alone, and the superiority of the combination of dorzolamide and timolol over brinzolamide and timolol in terms of improving ocular blood flow (retrobulbar Color Doppler Imaging - CDI parameters) as well as in terms of visual field preservation in glaucoma patients over 4 to 5 years. Conclusion: For the first time one study could demonstrate that an improvement in ocular blood flow in the long run results in preservation of visual field in glaucoma patients. Dorzolamide, combined with the beta-blocker timolol, seems to be superior in this regard to brinzolamide plus timolol.