Visual side effects of scopolamine/ dextroamphetamine among parabolic fliers

Scopolamine/dextroamphetamine has been used to combat motion sickness generated aboard research aircraft for decades. While it has shown to be effective, previous studies differ as to the presence of visual side effects secondary to scopolamine's anticholinergic properties. This study sought to quantify any such effects in order to determine if they are operationally significant.

Fliers in NASA's Reduced Gravity Program received a weight-based dose of scopolamine/ dextroamphetamine prior to boarding the aircraft. Measurements of pupil size, visual acuity, and accommodation were taken in identical conditions using subjects' dominant eyes prior to medication administration and again after landing. We enrolled 131 subjects ages 18-48. Pre- and postflight measurements of pupil size and acuity were available for 125 subjects.

Average pupil size increased by 1.1 mm (95% CI 0.9-1.2). Only 1.6% of subjects experienced a change in visual acuity of greater than 10 ft. The average near-point accommodation changed from 8.61 to 7.84 diopters, a difference of -0.77 (-1.01 to -0.53) diopters or 1.34 cm (0.87-1.81). Increasing age also correlated significantly with worsening change in accommodation.

This study found statistically significant changes in pupil size and near point accommodation that do not appear to be clinically important. No significant decrement in acuity was noted. While direct effects on in-flight performance could not be assessed, the use of scopolamine/dextroamphetamine among fliers aboard research aircraft does not appear to yield visual side effects sufficient to compromise later ground operations.