Purpose. To objectively measure changes in the human ciliary muscle dimensions in vivo after instillation of topical phenylephrine, a mydriatic and vasodilating agent.
Methods. A cross-sectional study of 25 healthy young adults was conducted. Measurements of pupil size, accommodation, and ciliary muscle thickness were made both before and 30 min after instillation of 1% proparacaine and 2.5% phenylephrine. Accommodation was measured in three ways: subjectively using a push-up technique and Royal Air Force (RAF) rule, and objectively using both the Grand Seiko autorefractor and PowerRefractor. Images of the temporal ciliary muscle were acquired using the Visante Anterior Segment Optical Coherence Tomographer (OCT). Ciliary muscle images were objectively analyzed using a computer-based segmentation technique.
Results. Amplitude of accommodation using the push-up test was reduced by about 1 D with phenylephrine (p < 0.001). Phenylephrine did not change the accommodative response to a 4 D Badal target as measured by either autorefraction or photorefraction (p > 0.30). There was statistically significant thickening of the anterior region and thinning of the posterior region of the ciliary muscle with accommodation (p < 0.001, all locations). Phenylephrine did not affect either baseline ciliary muscle thickness or the accommodative contraction of the muscle (p > 0.09).
Conclusions. Low-dose phenylephrine does not affect ciliary muscle dimensions, ciliary muscle contractility, or accommodative response to a 4 D near target.
*OD, PhD, FAAO
‡MCOptom, PhD, FAAO
College of Optometry, The State University of New York, New York, New York (KR), College of Optometry, The Ohio State University, Columbus, Ohio (MDB, LTS, KZ), Department of Mathematics, The Ohio State University, Columbus, Ohio (C-YK), Department of Mathematics and Computer Science, Claremont McKenna College, Claremont, California (C-YK), and College of Optometry, University of Houston, Houston, Texas (MAB).
Received December 21, 2011; accepted June 11, 2012.
Kathryn Richdale SUNY College of Optometry 33 West 42nd St New York, NY 10036 e-mail: KRichdale@SUNYopt.edu