To the Editor.
—In a recent article in the Archives titled "Studies on Retinal Blood Flow: I. Estimation of Human Retinal Blood Flow by Slitlamp Fluorophotometry" (96:893-897, 1978), Cunha-Vaz and Lima describe a technique to estimate retinal blood flow that they have applied to studies in diabetic patients.1 We believe, based on our experience with the dyedilution technique and on a critical review of this article, that this technique is not adequate to determine retinal blood flow for the following reasons:
In the technique of Cunha-Vaz and Lima, a quantity that is designated as the "first appearance time" of fluorescein is measured at two sites 0.9 mm apart along the superior temporal artery and is used to calculate the minimal transit time (tm) of the dye between these two points. The mean value for tm is 0.17 seconds in normal subjects and 0.09 seconds in anemic patients.
Riva CE. Retinal Blood Flow. Arch Ophthalmol. 1979;97(1):173-174. doi:10.1001/archopht.1979.01020010095027