Short-term effects of caffeine intake on anterior chamber angle and intraocular pressure in low caffeine consumers

Background Acute caffeine consumption causes a transient increase in IOP; however, the mechanisms underlying this phenomenon remain unknown. This study aims to determine the structural changes in cornea and anterior chamber associated with caffeine ingestion. Methods Seventeen healthy low caffeine consumers ingested a capsule of caffeine ( 4 mg/kg) or placebo (300 mg of corn-starch) in a counterbalanced manner. We measured IOP by rebound tonometry and the anterior chamber depth (ACD), anterior chamber volume (ACV), anterior chamber angle (ACA) and central corneal thickness (CCT) with the Pentacam rotating Scheimpflug camera. Subjective feelings of arousal were also obtained. All the dependent variables were obtained before and 30, 60 and 90 min after caffeine/placebo intake. Results Caffeine intake caused an acute IOP rise (p = 0.005, eta(2) = 0.403) and a narrowing ACA (p = 0.028, eta(2) = 0.266). However, our data did not reveal any effect on CCT, ACD and ACV after caffeine ingestion (p = 0.798, p = 0.346, p = 0.175, respectively). Participants reported greater levels of activation after ingesting caffeine in comparison to placebo (p = 0.037, eta(2) = 0.245). Conclusion The IOP rise associated with caffeine intake may be caused by an ACA reduction, which may add resistance to the outflow of aqueous humour. The current results may be of special relevance for subjects at high risk for glaucoma onset or progression and may help to understand the mechanisms underlying caffeine-induced ocular hypertension.