Even modest intraocular pressure (IOP) elevations are thought to increase optic nerve damage. Many previous studies on the IOP-modifying effect of caffeine consumption have observed modest acute post-ingestion IOP increases over a one to four-hour period, ranging from 0-4 mmHg. There is also evidence of beneficial IOP reduction from low-intensity physical activity. The authors hypothesize that the consumption of caffeine prior to exercise counteracts the IOP reduction from low-intensity endurance exercise, and thus caffeine intake prior to exercise should be discouraged in patients performing low-intensity exercise. This double-masked, placebo controlled cross-over study is the first to assess whether caffeine consumption modified the effect of low-intensity endurance exercise on IOP.
The authors measured IOPs of eighteen subjects after ingesting either a caffeine pill (~4mg /kg) or placebo at various time points before, during, and after low-intensity endurance exercise. After 30 minutes of cycling, baseline caffeine dosing was associated with a 1.8 mmHg higher IOP compared to placebo. The authors found that the caffeine-related increase in IOP during low-intensity aerobic exercise was independent of heart rate response.
Although the data seems to confirm the author's hypothesis that caffeine consumption adversely modifies the IOP-reducing effect of low-intensity endurance exercise, there are factors that limit the generalizability and clinical significance of the results. Specifically, it is important to address the presence or absence of family history of glaucoma in the subjects, as well as their habitual caffeine consumption. Prior studies suggest these attributes could confound the study results.1,2 Furthermore, study participants were young and healthy, which limits study results applicability to glaucoma patients. Despite study limitations, which the authors give due consideration, this work raises awareness about the need to understand environment X environment interactions impacting IOP.