Large sample study of the effects of phenylephrine 2.5% eyedrops on the amplitude of accommodation in man.

A single drop of phenylephrine 2.5% (MYDFRIN) was instilled into the eyes of 160 volunteers (aged 20 to 30 years) and their amplitude of accommodation assessed under standard illumination using a push-up technique without an artificial pupil. The amplitude was assessed every 5 or 10 min over a period of 90 min. Within 30 min, nearly 75% of the subjects showed a measurable change in amplitude. Overall, the amplitude declined slowly with time to realize an average 11% reduction from an average starting amplitude of 10.7 D. A large range of responses from a 30% increase to a 60% decrease in amplitude was, however, observed. Subjects with large amplitudes of accommodation were more likely to show significant decreases while some subjects with smaller amplitudes showed an apparent increase in accommodation (r2 = 0.176). The phenomenon was observed in both blue- and brown-eyed subjects and in non-contact lens wearers and soft contact lens wearers (r2 values of 0.144 to 0.265).