Effect of Oral Caffeine on Eyelid Muscle Activity and Myokymia in Healthy Adults

Abstract

Background: Caffeine is a widely consumed methylxanthine stimulant that can influence central nervous system activity, neuromuscular excitability, and motor responsiveness. Eyelid myokymia is usually benign but may cause discomfort, anxiety, and reduced concentration, particularly in healthy adults exposed to stimulants, fatigue, stress, or prolonged screen use. Objective: To assess the acute effect of oral caffeine on eyelid muscle activity and eyelid myokymia frequency and severity in healthy adults. Methods: This quasi-experimental pre-test/post-test study included 50 healthy adults aged 18–40 years. Baseline eyelid muscle activity was measured using surface electromyography, and myokymia frequency and severity were recorded before caffeine intake. Participants then received a standardized 200 mg oral caffeine dose, and post-caffeine measurements were obtained after 30–60 minutes. Pre- and post-caffeine outcomes were compared using paired sample t-tests, and the relationship between eyelid muscle activity and myokymia frequency was assessed using Pearson correlation analysis. Results: Mean eyelid muscle activity increased from 2.5 µV before caffeine to 3.1 µV after caffeine, with a mean difference of 0.6 µV (p = 0.002). Mean myokymia frequency increased from 1.2 to 1.7 episodes/min, with a mean difference of 0.5 episodes/min (p = 0.0001). Myokymia severity remained predominantly mild, and eyelid muscle activity showed a moderate positive correlation with myokymia frequency (r = 0.45, p < 0.05). Conclusion: A single 200 mg oral caffeine dose was associated with significantly increased eyelid muscle activity and myokymia frequency in healthy adults, while severity remained mild