Blurred vision after instillation of topical carbonic anhydrase inhibitor

PURPOSE: The aim of this study was to compare brinzolamide with dorzolamide in regard to blurred vision after instillation. We also compared saline with two topical carbonic anhydrase inhibitor drugs. SUBJECTS AND METHODS: The study population comprised 21 healthy volunteers whose best corrected visual acuity was 1.0 or better. Brinzolamide 1% or dorzolamide 1% was applied to one eye the contralateral eye was exposed to the other drug. At 30 sec after instillation, visual acuity was measured every 30 sec until best visual acuity was recovered. Because visual acuity can fluctuate widely with blinking, subjects blinked for 5 sec before visual acuity measurement. As control, we applied saline alone to both eyes of 14 subjects and measured the change in visual acuity in the same way. Subjective sensations in each eye were recorded after measurement. RESULTS: Average visual acuity every 30 sec for 5 min was 0.41, 0.56, 0.68, 0.86, 0.87, 0.96, 1.04, 1.08, 1.11, and 1.12 after dorzolamide instillation, and 0.28, 0.42, 0.60, 0.69, 0.81, 0.91, 0.93, 0.99, 1.06, and 1.10 after brinzolamide instillation. In contrast, the average visual acuity after saline instillation for 2 min was 1.09, 1.13, 1.16 and 1.16. Of the 21 subjects, 15 (71.4%) felt moderate or severe irritation when dorzolamide was instilled; 2 (9.5%) felt moderate or severe irritation when brinzolamide was instilled. CONCLUSIONS: Both brinzolamide and dorzolamide caused significantly prolonged blurring of vision, from 30 sec to 2 or 3 min after instillation, as compared with saline only. The average visual acuity after brinzolamide instillation was lower than after dorzolamide for 5 min after instillation, although there was no significant difference. Judging from the subjects' sensations, it is suggested that with dorzolamide the prolonged blurred vision was due to reflex tearing from irritation, as explained above, whereas with brinzolamide it was due to opaque tears on the ocular surface.