Influence of the Time Interval Between Instillation of Two Drops of Cyclopentolate 1 % on Refraction and Dilation of the Pupil in Children C. STOLOVITCH, M.D., Y. ALSTER, M.D., A. LOEWENSTEIN, MD., AND M. LAZAR, M.D. • PURPOSE: Because the usual length of time to instill two drops of cyclopentolate 1 % (five to ten minutes) is time-consuming and inconvenient to clinical staff as well as to the child and the child's parents, we investigated the influence of the time interval between the instillation of the two drops on refraction and mydriasis in children. • METHODS: We conducted a crossover study on 48 children at the Tel-Aviv Medical Center. Gen- der, iris color, ethnic origin, and age were record- ed. Two cyclopentolate 1 % eyedrops were instilled at a one- or five-minute time interval. Retinoscopy was performed and the mydriatic effect was record- ed. One week later, the procedure was repeated, this time with a different time interval. • RESULTS: The time interval between the instil- lation of the two drops had no significant influence on retinoscopy results (P = .65 and P = .50 for right and left eyes, respectively) or on pupil dila- tion (P = .377 and P = .113 for right and left eyes, respectively). • CONCLUSIONS: Instilling two drops of cyclo- pentolate 1% one minute apart is as effective as instilling them five minutes apart. Accepted for publication Oct. 26, 1994. From the Department of Ophthalmology, Tel-Aviv Medical Center, Israel. Reprint requests to C. Stolovitch, M.D., Depattment of Ophthal- mology, Tel-Aviv Medical Center, 6 Weizman St., Tel-Aviv 64239, Israel; fax: 972-3-5469580. R EFRACTION UNDER CYCLOPLEGIA IS A ROUTINE pédiatrie examination, especially in esotropic children. Among the medications used to achieve cycloplegia, cyclopentolate is the one most widely used. It is generally agreed that one drop is not sufficient and that at least two drops are needed. However, controversy exists among pédiatrie ophthal- mologists concerning the minimal time interval re- quired between the instillation of the two drops to attain satisfactory cycloplegia. Pharmacokinetic con- siderations determine that instilling any two drops one directly after the other would not be more effective than instilling only one drop, since a large volume of the instilled drug would be washed out and wasted. 1 ' 3 As for cyclopentolate instillation in particu- lar, Rosenbaum and associates 4 recommended a five- minute interval to be optimal between drops, Ingram and Barr 5 favored a ten-minute interval, and Robb and Peterson 6 waited a few minutes between drops. The current common practice of cyclopentolate in- stillation, which requires a five- to ten-minute interval between administering the two drops, is time-con- suming andnnconvenient to the clinical staff as well as to the child and the child's parents. Geyer, Godel, and Lazar 7 previously showed that instilling two different drugs, tropicamide and phenyl- ephrine, one after the other had an effect on pupil dilation equal to that of instilling the drugs ten minutes apart. Loewenstein and associates 8 also dem- onstrated that the effect of instilling two drops of the same drug one after the other is 30% to 35% stronger than the effect attained by a single drop. In the VOL.119, No. 5 © AMERICAN JOURNAL OF OPHTHALMOLOGY 119:637-639 637