Acute Effects of Caffeine on Ocular Functions in Young Adults

To assess the short-term effects of a standardized dose of caffeine on selected ocular parameters in young adults and to examine its possible influence on visual performance during screen-based activities.

This prospective experimental study included 52 healthy university students aged 18-30 years. Participants consumed a standardized dose of 240 mg of caffeine in the form of black coffee. Ocular parameters including intraocular pressure (IOP), pupil diameter, contrast sensitivity, near point of accommodation, accommodative facility, vergence facility, visual reaction time, stereopsis, and ocular motility were assessed before and 30 minutes after caffeine intake. Pre- and post-intervention measurements were compared using paired t-tests, with p<0.05 considered statistically significant.

Significant improvements were observed in accommodative facility (right eye [OD]: p=0.04; left eye [OS]: p<0.001; both eyes [OU]: p=0.0003), vergence facility (p=0.01), and contrast sensitivity in OU (OD and OS: p<0.001). The near point of accommodation decreased significantly, indicating improved accommodative ability (OD: p=0.02; OS: p=0.009; OU: p<0.001). Visual reaction time improved in most participants, although the change was not statistically significant (p=0.08). Pupil diameter increased significantly (p<0.001). IOP showed a small but statistically significant increase (p<0.001), remaining within normal physiological limits. Changes in stereopsis were not statistically significant (p=0.06). Minor changes were also observed in saccadic and pursuit eye movements.

A single dose of caffeine led to measurable short-term improvements in visual performance, particularly in accommodation and contrast sensitivity, along with a modest improvement in reaction time. Small increases in pupil diameter and IOP were also observed. These findings suggest that moderate caffeine intake may offer some benefit during visually demanding tasks. However, caution may be needed for individuals at risk of ocular hypertension. Larger, placebo-controlled, and multicenter studies are recommended to confirm these findings and to evaluate long-term effects.