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Larry Kagemann, Alon Harris, Hak Sung Chung, Christian P. Jonescu-Cuypers, Drora Zarfati, Bruce Martin; Photodetector Sensitivity Level and Heidelberg Retina Flowmeter Measurements in Humans. Invest. Ophthalmol. Vis. Sci. 2001;42(2):354-357.
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purpose. In vitro models suggest that Heidelberg retina flowmeter (HRF)
measurements are affected by changes in photodetector sensitivity. We
measured blood flow in a single volume of human retinal tissue in vivo
at various sensitivity (DC) levels.
methods. The peripapillary retinal regions of 12 normal subjects were examined
by HRF under five different sensitivity settings: (1) average DC range
below 100; (2) average DC range below 125; (3) average DC range near
150 (normal sensitivity); (4) average DC range above 175; and (5)
average DC range above 200 or extremely overexposed. The distributions
of flow values were examined by pointwise analysis. All pixels from a
common tissue location were analyzed, and the effect of their
brightness on the flow measurement was evaluated by ANOVA with
Fisher’s protected least significant difference model.
results. ANOVA analysis of image DC level showed that significantly different DC
levels were achieved for each of the five sensitivity settings
(P < 0.0001). Flow values decreased with increasing DC
for each of the 25th percentile, 50th percentile (P <
0.0001 for each), 75th percentile (P = 0.0026), 90th
percentile (P = 0.0216), and mean (P =
0.0004) flow values. The percentage of pixels with values of zero
(avascular tissue) increased with increasing photodetector sensitivity
(P < 0.0001).
conclusions. Improper sensitivity settings alter the detected percentage of
avascular tissue and the blood flow measurements in tissue containing
capillaries. Consistent assessment of retinal blood flow requires
consistent photodetector sensitivity settings between longitudinal
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