Effect of Aging on Nocturnal Blood Flow in the Optic Nerve Head and Macula in Healthy Human Eyes

PURPOSE: To study the effect of aging on 24-hour blood flow in the optic nerve head and macula of healthy human eyes. METHODS: Fifteen older volunteers with healthy eyes (age 50 to 80 y) and 15 healthy younger volunteers (age 20 to 25 y) were housed for 1 day in a sleep laboratory. Every 2 hours, blood pressure and intraocular pressure (IOP) were measured after 5 minutes in the sitting position. Ocular perfusion pressure was calculated. Indices of blood volume, flow, and velocity in the optic nerve head and macula were measured using a scanning laser Doppler flowmeter at the same time points. RESULTS: Within the group of older subjects, nocturnal IOP was significantly lower than diurnal IOP. There was no significant difference in the ocular perfusion pressure between the 2 time periods. However, there were statistically significant decreases (6.8% to 16.8%) in the ocular blood flow parameters from the diurnal period to the nocturnal period. Within the group of younger subjects, nocturnal IOP was higher and nocturnal ocular perfusion pressure was lower than the corresponding diurnal values. There was no significant difference in any ocular blood flow parameter between the diurnal and nocturnal periods. Comparing the older and younger subject groups, nocturnal ocular perfusion pressure was higher in the older group. CONCLUSIONS: Significant diurnal-to-nocturnal decreases in blood flow occurred in the optic nerve head and macula in the older subjects, but not in the younger subjects. These diurnal-to-nocturnal change patterns in ocular blood flow were independent of the change patterns in ocular perfusion pressure.