INFLUENCE OF ACQUISITION PARAMETERS ON HEMODYNAMIC MEASUREMENTS WITH THE HEIDELBERG RETINA FLOWMETER AT THE OPTIC DISC

Purpose: The Heidelberg Retina Flowmeter (HRF; Heidelberg Engineering GmbH, Heidelberg, Germany) is a new instrument that determines hemodyn amic variables at discrete locations of the retina and the optic disc. The objective of this study was to evaluate the influence of various HRF recording settings on the long-term variability of the HRF paramet er, ''Flow,'' computed at the optic nerve head in healthy individuals. Methods: The authors obtained 2 sets of 5 HRF recordings in 10 health y individuals (age range, 23-60 years). The HRF recordings were obtain ed within a scan area of 10 degrees x 2.5 degrees (set 1) and 20 degre es x 5 degrees (set 2). For each set, the HRF recordings were obtained on 5 consecutive days. Respective HRF recordings for both sets were o btained on the same days. On these recordings, the HRF parameter, ''Fl ow,'' was computed at 3 different regions of interest (temporal superi or, temporal inferior, and temporal rim of the optic disc). At all thr ee locations, Flow was computed within windows of measurement of 10 pi xels x 10 pixels and 20 pixels x 20 pixels. The effect of larger windo ws (30 pixels x 30 pixels, 40 pixels x 40 pixels, and 50 pixels x 50 p ixels) was tested at the temporal rim of the optic disc. Results: The highest reliability coefficient was reached with a scan area of 20 deg rees x 5 degrees at the temporal superior rim of the optic disc (r = 0 .93). Within a scan area of 20 degrees x 5 degrees, the size of the us er-defined measuring window did not influence the reliability. Two mod els of analysis of variance disclosed that the only effect on the comp uted value of Flow that reached statistical significance was that beca use of the scan area (F = 11.172; p = 0.001). The location of the wind ow of measurement and its size had no statistically significant effect . Conclusion: The present results show that the location of the window of measurement has an important effect on the long-term variability o f the HRF parameter, Flow. In addition, different scan areas influence significantly the computed values of this parameter.