Retinal mean transit time determined with an impulse‐response analysis from video fluorescein angiograms

PURPOSE: To evaluate a new technique for determining the Mean Transit Time (MTT) of retinal circulation, based on an impulse-response analysis. The results obtained were compared to those obtained with a conventional method based on semilogarithmic extrapolation. METHODS: 128 frames at a rate of 5 frames per second were digitized from video fluorescein angiograms and processed with a specially designed image analysis system. The MTT was determined from 25 curve pairs from 12 eyes in 8 young, healthy volunteers by the conventional technique (MTT[SLOPE]) and by our newly developed Impulse-Response analysis (MTT[IR]). RESULTS: MTT(SLOPE) and MTT(IR) calculated for the 25 curve pairs were 3.54 +/- 1.00 and 2.67 +/- 0.88 seconds, respectively (Mean +/- SD). There was a good correlation between the two techniques (r2 = 0.81, p < 0.001). Unlike MTT(SLOPE), MTT(IR) could be calculated also from curves with a badly defined bolus. CONCLUSION: We conclude that MTT(IR)-analysis of the retinal circulation may be used for clinical studies on retinal blood flow from angiograms obtained in patients.