Effect of Caffeine on Retinal Arteriolar Vascular Reactivity in Young, Normal Subjects

Abstract

The purpose was to compare the effect of various caffeine dosages on retinal arteriolar blood flow. Measurements were collected using laser Doppler flowmetry and densitometry, permitting the noninvasive simultaneous measurement of blood velocity and vessel diameter to derive blood flow. A double blind, triple crossover design was used. Measurements were collected from 12 healthy subjects (21-30yr) before and for 2hr after the ingestion of 200 or 400mg of caffeine, or placebo (each in tablet form). Subjects did not ingest caffeine for 24hr prior to data collection. All subjects were tested for all dosages with a period of 1 week between visits. Data analyses were performed using repeated measures ANOVA, with statistical significance set at p<0.05. Caffeine did not significantly affect retinal arteriolar diameter, blood velocity, blood flow or the ratio of maximum to minimum blood velocity. However, over the 2-hour study period, vessel diameter (p<0.0001), flow (p=0.03) and max:min ratio (p=0.00001) decreased significantly for all dosages, including placebo. Baseline blood pressure and pulse rate did not differ across dosages or across test days. Both systolic (p=0.01) and diastolic (p=0.0001) BP increased significantly for all dosages following drug administration, while PR decreased significantly (p<0.0001). Subjects in all treatment conditions experienced decreased arteriolar diameter, blood flow, max:min ratio and PR over the 2-hour study period whereas BP increased in all groups. These effects were independent of caffeine / placebo dosage. This suggests that the common precaution of banning caffeine ingestion for 24 hours prior to study data collection may be unnecessary.