A Comparison of Pupillary Dilation Velocity Using Tropicamide 1% and Phenylephrine 2.5%

Abstract

Purpose:: The purpose of this study is to compare the effects of tropicamide 1% and phenylephrine 2.5% on human pupillary dilation. Age, gender, iris color and refractive error were studied to see their effect on the velocity of pupillary dilation.

Methods:: Twenty-eight (28) patients needing a dilated fundoscopic exam were selected from an ophthalmology clinic. One drop of tropicamide 1% was instilled into the right eye. One drop of phenylephrine 2.5% was given to the left eye. Each patient therefore served as their own control. A Colvard pupillometer was used to measure the pupils of each eye at 0 , 2, 4, 6, 8, and10 minutes after the administration of the drops. The eyes were measured in a dark room using infrared light. The age, iris color, gender and refractive error of the patients were recorded. Statistical analyses were conducted using the mixed model analysis with linear regression.

Results:: The average age of the subjects was 65.3 years. The standard deviation was 14.9 years. After adjusted for age in the statistical regression model, pupil size was estimated to enlarge 0.18 and 0.09 millimeters per minute for the tropicamide treated eyes and for the phenylephrine treated eyes, respectively. There was a statistically significant difference between these two groups (p<0.0001). Age, gender, iris color, and refractive error did not have a statistically significant impact upon the velocity of pupillary dilation.

Conclusions:: Tropicamide 1% dilates pupils approximately twice as fast as phenylephrine 2.5%. Pupils dilated with tropicamide 1% also achieved a greater absolute pupillary dilation after ten minutes compared to phenylephrine 2.5%. Clinicians who wish to achieve the fastest and greatest pupillary dilation for their patients should use tropicamide 1% as opposed to phenylephrine 2.5%. Conversely, clinicians may wish to use phenylephrine 2.5% if they do not wish to achieve maximal pupillary dilation which may be beneficial in situations such as driving after a dilated eye exam. Age, gender, iris color, and refractive error did not effect the velocity of pupillary dilation. The medications appeared to dilate the eyes uniformly across our patient population. Human pupil size is a predominantly parasympathetically controlled phenomenon since a parasympatholytic agent (tropicamide) effects pupil size greater than a sympathomimetic agent (phenylephrine).

Keywords: pupil • drug toxicity/drug effects