Effect of phenylephrine on static and dynamic accommodation

Abstract

Purpose : The effect of phenylephrine on accommodation is unclear: whereas some studies report that phenylephrine reduces accommodative ability of the eye, others report that it has no effect. We tested the hypothesis that changes in accommodation are due to changes in optics and not in the function of the ciliary muscle.

Methods : The effect of phenylephrine on static accommodation was assessed for 8 eyes by computing the stimulus-response curve from the wavefront obtained at different vergences. Measurements were taken with the IRX3 commercial aberrometer for natural pupils before and after instillation of 2 drops of 10% phenylephrine. From these curves, we calculated the objective amplitude of accommodation (AA) and the accommodative response (AR) up to 6 D; the range of accommodative demands in which the pupil size did not decrease substantially after instillation. The effect of phenylephrine on dynamic accommodation was assessed for 6 eyes by measuring the AR at 10 Hz to a sinusoidally moving stimulus seen through a 3-mm pupil. The stimulus moved between 1 D and 3 D from the far point at 0.2 Hz. Measurements were taken with a custom-made optical system. From the results we computed the gain and phase of the responses. AR was calculated taking into account the effects of high-order aberrations (minimum RMS refraction) or without them (paraxial refraction).

Results : For static accommodation with the minimum RMS calculation of AR, the mean AA (and 95% confidence interval) changed after phenylephrine instillation by 0.51 D (0.14 D, 0.88 D). The change of the AR at a 6 D of accommodative demand was 1.00 D (0.64 D, 1.36 D). However, the values obtained for paraxial AR were –0.20 D (–0.55 D, 0.15 D) and 0.22 D (–0.20 D, 0.64 D), respectively. For dynamic accommodation, we found a mean difference in the AR gain of 0.09 D (–0.10 D, 0.19 D) with minimum RMS and -0.08 D (–0.14 D, 0.02 D) for paraxial refraction.

Conclusions : Whereas we found a clear, statistically significant decrease in AR after the instillation of phenylephrine, we did not find any effect on static and dynamic accommodation when high-order aberrations were not taken into account in the calculation of AR. As paraxial refraction depends mainly on the ciliary muscle, its function seems to be unaffected by phenylephrine according to our results. Differences in reported effects of phenylephrine may be due to the methods used to calculate the AR.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.