Short-term effects of caffeine intake on binocular accommodative facility: a quantitative and qualitative analysis

Background: This placebo-controlled, double-blind, balanced crossover study aimed to assess the acute effects of caffeine ingestion on the frequency and precision of the binocular accommodative facility. Methods: Twenty university students (21.9 +/- 3.4 years) ingested a capsule of caffeine (4 mg/kg) or placebo (300 mg of corn-starch) on two different days and counterbalanced order. The binocular accommodative facility was objectively assessed, using the WAM-5500 binocular open-field autorefractometer, after 60 min of capsule ingestion (caffeine/placebo). Perceived levels of activation was also assessed in each experimental condition. Results: The ingestion of a single administration of caffeine (similar to 4 mg/kg) causes an increase in the number of cycles performed per minute (p = 0.023, Cohen's d = 0.55), whereas no effects were observed for the mean magnitude of accommodative change between the far and near targets (p = 0.794), and the percentage of incorrect cycles of accommodation and dis-accommodation (p = 0.271 and 0.396, respectively). Participants reported a perceived level of activation of 6.8 +/- 1.5 and 7.6 +/- 1.8 in the placebo and caffeine conditions, respectively (p = 0.059). Conclusion: Caffeine intake improves quantitative, but not qualitative, measures of accommodative facility. These results corroborate the impact of caffeine on visual function and suggest that this ergogenic effect of caffeine may be used to enhance visual performance in applied situations.

Automated summary

The study showed that caffeine intake can increase the number of cycles performed in binocular accommodative facility, but does not affect the magnitude of accommodative change between targets or the percentage of incorrect cycles. Participants reported slightly higher levels of perceived activation after taking caffeine compared to taking a placebo.