Laser refractive surgery patients may experience starbursts and streaks, especially under mesopic conditions. This makes the influence of pupil width in comparison with that of the optical zone a key issue. At night, when the ablation zone is smaller than the pupil diameter, photic phenomena is more likely to occur.

My colleagues and I recently evaluated the influence of topically applied brimonidine (Alphagan; Allergan, Irvine, California) and dapiprazole (Remydrial; Winzer Pharm GmbH, Olching, Germany) on pupil size under various levels of illumination. We found that the two agents similarly reduced pupil mydriasis at scoptopic illumination levels. Brimonidine had a slightly stronger effect, however, and should be applied 20 minutes prior to night activities or in dimly lit areas in patients who experience photic phenomena after refractive surgery.

Brimonidine, an alpha-2 agonist, reduces aqueous humor production and increases uveoscleral outflow in the treatment of glaucoma. Dapiprazole blocks the effect of phenylephrine as an alpha-1 antagonist. The latter agent prevents accommodation spasm and has no effect on the ciliary muscle or the scleral spur. No patients in our study experienced side effects associated with either treatment.

METHODS
We prospectively evaluated brimonidine tartrate 2 mg/mL and dapiprazole HCl 5 mg/mL in a randomized trial. We included 19 healthy patients with no ocular pathologies. Each patient was given both solutions, one in each eye, for intraindividual comparison. Pupil size was measured with a pupillometer (Procyon, UK) before and after topical administration of the drugs. The change in pupil size was noted. Pupillometer measurements were taken under scotopic conditions (0.03 lux), low mesopic conditions (0.82 lux) and high mesopic conditions (6.4 lux). Each eye was measured at 20, 40, 60 and 180 minutes after drug application.

The baseline changes in pupil diameter were compared intraindividually by computing the intraindividual difference between the diameter change under brimonidine subtracted from the diameter change under dapiprazole. The clinical endpoints of the study were the intraindividual differences of the pupillary diameter changes between the two agents. A P value of <.05 indicated local statistical significance because of the exploratory nature of this study.

Pupil dilation was only slightly under scotopic conditions following the application of both agents. After 20 minutes, the median reduction in pupil width was 1.4 mm for brimonidine and 0.9 mm for dapiprazole, a statistically significant effect for both drugs (P<.001). After 40 minutes, the maximum effect was reached and remained stable through the next measurement at 180 minutes. We found that under mesopic lighting conditions, there was only a slight effect of <1 mm. Brimonidine was more effective than dapiprazole at all time points, a difference that was statistically and clinically significant (Figure 1).

Knowledge of preoperative pupil size is important for guiding surgical planning toward the avoidance of nighttime photic phenomena. The difference between the functional optical zone and the size of the pupil at night and in low-light conditions is critical. If the pupil size is larger than the functional optical zone, starbursts and streaks may occur.

Based on our results, it may be prudent to recommend brimonidine to patients who report photic phenomena following refractive surgery. A single installation, 20 minutes before activities in dimly lit conditions, should be sufficient. We should note that independent proof of efficacy for brimonidine versus a placebo control that considers pupil size reduction and clinical benefit for patients with photic phenomena after refractive procedures is warranted.

H. Burkhard Dick, MD, is director of the department of ophthalmology, University Eye Hospital, Knappschaftskrankenhaus-Bochum-Langendreer, in Germany. Professor Dick is a member of the CRSToday Europe Editorial Board. He states that he holds no financial interest in the products or companies mentioned. Professor Dick may be reached at burkhard.dick@kk-bochum.de or +49 234 299 3101.

1. Marx-Gross S, Krummenauer Frank, Dick HB, Pfeiffer N. Brimonidine versus dapiprazole: influence on pupil size at various illumination levels. J Cataract Refract Surg. 2005;31:1372-1376.