Effects of caffeine on microcirculation of the human ocular fundus

PURPOSE: To determine the effect of caffeine on microcirculation in the human ocular fundus. METHODS: The microcirculation in the ocular fundus of 10 healthy volunteers (10 eyes) was studied using a laser speckle tissue circulation analyzer. Caffeine or placebo (100 mg) was administered orally in a double-masked manner. Square blur rate (SBR), a quantitative index of blood flow velocity, was measured in a temporal site of the optic nerve head (ONH) free of surface vessels and in a middle site of the choroid-retina between the ONH and macula. Intraocular pressure (IOP), blood pressure (BP), pulse rate (PR), and central critical fusion frequency (CFF) were also measured. These parameters were measured before and for 2 hours after administration. The area under curve (AUC) of SBR was calculated for each area. Ocular perfusion pressure (OPP) was also calculated from BP and IOP. RESULTS: The time-course of change in SBR value showed much individual difference. Caffeine decreased the AUC of SBR in the ONH (P =.0218) as well as in the choroid-retina (P =.0469) significantly. IOP, mean BP, PR, OPP, and central CFF did not change significantly. CONCLUSIONS: These results suggest that caffeine may increase blood vessel resistance and decrease blood flow in the human ONH and choroid-retina.