Eric Denion1, Frédérique Charlot, Guillaume Béraud. 1. 1Centre Ophtalmologique du Pays des Olonnes (COPO), Les Sables-d'Olonne, France 2Service d'Ophtalmologie, Polyclinique de la Baie, Saint-Martin-des-Champs, France 3Médecine Interne et Maladies Infectieuses, Poitiers, France 4Université Droit et Santé Lille 2, Lille, France 5Interuniversity Institute for Biostatistics and Statistical Bioinformatics, Hasselt University, Hasselt, Belgium.
Abstract
PURPOSE: Patients are usually advised to wait 5 minutes between eye drops. This delay supposedly allows the first drop not to be washed out by the second one, thereby increasing the combined effect. However, in the only experimental study conducted in humans on the concurrent administration of two different eye drops, the authors concluded that a 10-minute time interval between eye drops did not increase their combined effect. Our study was designed to address this puzzling observation. METHODS: Using digital photographs shot in photopic conditions in 40 eyes of 20 healthy volunteers, we compared relative pupil surface (i.e., pupil to iris surface area ratios) before and after the administration of one drop of 10% phenylephrine and one drop of 0.5% tropicamide either immediately or after a 5-minute time interval. RESULTS: Waiting 5 minutes yielded a 5.6% relative pupil surface gain (observer 1: P = .003, observer 2: P = .005) indicating an additional combined effect with a 5-minute time interval. CONCLUSIONS: These results show a detectable additive effect that is probably the result of methodological refinements including the challenging of the mydriasis by photopic conditions and the use of pupil and iris surface areas, which may show differences that would be undetectable in terms of diameter.
PURPOSE:Patients are usually advised to wait 5 minutes between eye drops. This delay supposedly allows the first drop not to be washed out by the second one, thereby increasing the combined effect. However, in the only experimental study conducted in humans on the concurrent administration of two different eye drops, the authors concluded that a 10-minute time interval between eye drops did not increase their combined effect. Our study was designed to address this puzzling observation. METHODS: Using digital photographs shot in photopic conditions in 40 eyes of 20 healthy volunteers, we compared relative pupil surface (i.e., pupil to iris surface area ratios) before and after the administration of one drop of 10% phenylephrine and one drop of 0.5% tropicamide either immediately or after a 5-minute time interval. RESULTS: Waiting 5 minutes yielded a 5.6% relative pupil surface gain (observer 1: P = .003, observer 2: P = .005) indicating an additional combined effect with a 5-minute time interval. CONCLUSIONS: These results show a detectable additive effect that is probably the result of methodological refinements including the challenging of the mydriasis by photopic conditions and the use of pupil and iris surface areas, which may show differences that would be undetectable in terms of diameter.