Caffeine is known to penetrate many bodily fluids, including the vitreous. In this prospective study, investigators measured caffeine levels in vitreous samples from patients undergoing vitrectomy and epiretinal membrane peel. Patients were divided into habitual and non-habitual coffee drinkers. One hour prior to vitrectomy, 10 of 25 habitual coffee drinkers ingested three espressos containing a total of 180mg of caffeine. The remaining patients received no caffeine before surgery. Vitreous samples were taken with the vitreous cutter just prior to vitrectomy. Caffeine levels were significantly higher in samples taken from habitual coffee drinkers compared to non-habitual drinkers. Between habitual coffee drinkers, there was no significant difference in vitreous caffeine levels, even if they had consumed coffee preoperatively. This study, while intriguing, should be considered preliminary in nature. It does, however, allow for further research into clinically relevant effects of caffeine on the retina and vitreous. The authors cite the antioxidant and UV-A absorbing properties of caffeine as possible future areas of study.