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

Purpose: To evaluate a new technique for determing 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 (MTTSLOPE) and by our newly developed Impulse-Response analysis (MTTIR). Results: MTTSLOPE and MTTIR 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 (r(2) = 0.81, p<0.001), Unlike MTTSLOPE MTTIR could be calculated also from curves with a badly defined bolus. Conclusion: We conclude that MTTIR-analysis of the retinal circulation may be used for clinical studies on retinal blood flow from angiograms obtained in patients.