Brimonidine and pupillary diameter

Abstract

Drs. Derick and coworkers recently published the interesting article “Brimonidine Tartrate. A One-month Dose Response Study.”1Derick R.J. Robin A.L. Walters T.R. et al.Brimonidine tartrate a one-month dose response study.Ophthalmology. 1997; 104: 131-136Abstract Full Text PDF PubMed Scopus (125) Google Scholar This multicenter study indicates that brimonidine 0.2% is well tolerated, efficacious, and shows potential as an agent in the long-term treatment of elevated intraocular pressure. In the “Method” section they state that at the baseline visit, measurement of pupillary diameter was performed using a millimeter ruler. Pupil size was measured also during follow-up examinations in the morning on days 7, 14, 21, and 28. The patients were instructed not to use the study medication until after the early morning (7:30 am-9:30 am) examination. In the “Results” section, the authors report no clinically significant changes in mean pupil size. It is unclear whether during follow-up examination pupillary diameter measurement was performed only before brimonidine instillation or both before and after the instillation. In the first instance, which is the most likely to have been performed, pupil size evaluation was made at least 8 hours after the last brimonidine instillation, the previous evening. In that case, the acute effect of brimonidine on pupil size was not assessed. In our current study on the acute effect of 0.2% brimonidine on short-wavelength automated perimetry in 60 ocular hypertensive patients (unpublished data), a significant decrease in pupillary diameter was evident in 100% of eyes comparing preinstillation and postinstillation (60 minutes later) diameter, as assessed by auto-pupil measurement by Humphrey Field Analyzer 2 model 750 and by using a millimeter ruler. In their recent clinical study, Schuman et al2Schuman J.S. Horwitz B. Choplin N.T. et al.Chronic Brimonidine Study GroupA 1-year study of brimonidine twice daily in glaucoma and ocular hypertension. A controlled randomized, multicenter clinical trial.Arch Ophthalmol. 1997; 115: 847-852Crossref PubMed Scopus (186) Google Scholar have observed no clinically significant differences in pupil size between the brimonidine and timolol groups throughout the 1-year followup. Mean changes in pupil size ranged from −0.13 to −0.22 mm with brimonidine and from 0.07 to −0.17 mm with timolol. However, also in this study, it is unclear when pupillary diameter measurement was performed. Undoubtedly, evaluation of pupillary diameter changes was not one of the main outcome measures of Dr. Derick et al’s excellent contribution to the knowledge of brimonidine. However, we believe that changes in pupil size should be carefully assessed because of the possible role of miosis (linked to prostaglandins release?) on the mechanism of action of the drug and its implications for perimetric follow-up and visual quality. Brimonidine and pupillary diameter: Authors’ replyOphthalmologyVol. 105Issue 8Preview Full-Text PDF