Ocular response to energy drink consumption: A pre-post analysis of visual fatigue in young adults in Trinidad and Tobago

Background: Energy drink consumption is highly prevalent among university students, yet its acute effects on near visual function and ocular physiology is limited. This study determined the effects of caffeinated energy drink on near visual acuity (VA), pupil size, and amplitude of accommodation (AOA) among a sample of university students. 

Materials and Methods: A prospective clinical experiment was conducted at the University of the West Indies Optometry Clinic among regular consumers of caffeinated products. Participants underwent baseline assessments of near VA, AOA, pupil size, and Body Mass Index (BMI). VA, AOA, and pupil size measures were repeated thirty minutes and one hour after consumption of energy drink containing 125 mg of caffeine. 

Results: Fifty-seven participants (56.1% female and 43.9% male) were assessed. No significant sex differences were found between BMI, and any visual outcome at any point (p > 0.05). Paired samples t-tests revealed a significant increase in pupil size at 30 minutes (mean increase =0.29 mm) and one hour (mean increase =0.60 mm) post-consumption (p <0.001). AOA increased significantly at 30 minutes (mean increase= 0.77D, p = 0.024), but declined significantly between 30 to 60 minutes time point (mean decrease = 0.68D, p = 0.015). Near VA showed a minor but statistically significant decrease at 30 minutes (p = 0.020), and not at1 hour post consumption. There were strong correlations between the pre-test and post-test measurements for near visual acuity and pupil size (r = 0.844–0.928), whereas the correlation between the pre-test and post-test accommodation measurements was moderate (r = 0.46–0.66). 

Conclusions: Caffeinated energy drinks momentarily increased pupil size and accommodation, with minimal impact on near VA. These transient changes may offer short-term visual benefits but are unlikely to sustain visual performance during prolonged near tasks.