Feke and Rizzo observed our omission of their article1 regarding the effects of aging on optic nerve head circulation. Their primary finding that optic nerve head capillary blood speed increases from approximately age 15 to 35 years and then declines steadily through the eighth decade strongly suggests that aging influences optic nerve head perfusion in parallel with its effect on the cerebral and retinal circulations. This work by Rizzo et al was performed using Riva's laser Doppler technique, which was the best technique available then, although it suffers from several shortcomings. The laser Doppler flowmetry technique does not contain a confocal aperture, and therefore data collected from the optic nerve head will include flow measurements from many different tissue layers. The article by Groh et al,2 which concluded that there was no significant difference in optic nerve head blood flow with age, was performed with newer ophthalmic laser Doppler technology; ie, the Heidelberg retinal flowmeter. Their findings in the optic nerve head conflicted with previous findings, although their measurements in the surrounding retinal tissue did show differences with age. We attributed this modification in our understanding of optic nerve head hemodynamics to technological advances. The Heidelberg retinal flowmeter also has limitations in its ability to make measurements in the optic nerve head, but based on our experience with both Heidelberg retinal flowmetry and laser Doppler flowmetry techniques, we chose to present the more current data.
Harris A, Ciulla TA, Chung HS, Martin B. Regulation of Retinal and Optic Nerve Blood Flow. Arch Ophthalmol. 1999;117(7):978-979. doi: