The effect of caffeine on pupil size and accommodation
Reviewed by Kurt Spiteri Cornish

Twenty-two young and healthy participants were recruited in this study. The authors showed that pupil size increased as a result of caffeine consumption. A more stable (lower variability of accommodation) accommodative response (AR) was induced by caffeine intake, whereas the accuracy of accommodation was insensitive to caffeine. It is postulated that the reason for this is the differences in the role of both autonomic nervous system pathways (parasympathetic more involved in the control of accommodation), as the effects of caffeine are manifest through the sympathetic pathway (by binding adenosine receptors). The authors acknowledged that different doses of caffeine and time frame could lead to different behaviour of ocular variables.

Acute effects of caffeine on dynamic accommodative response and pupil size in placebo-controlled double-blind balance crossover study.
Redondo B, Vera J, Carreño-Rodríguez C, et al.
CURRENT EYE RESEARCH
2020;45(9):1074-81.