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D Flitcroft, G Quinn, E Francis, P Parekh, G Schmid, RA Stone, M Maguire; Digital Signal Analysis of Laser Doppler Interferometry (LDI) Waveform Profiles: Increasing Reliability and Information Content . Invest. Ophthalmol. Vis. Sci. 2002;43(13):359.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Laser Doppler interferometry (LDI), a technique with purported high accuracy in measuring ocular axial length (AL), produces retinal signals with multiple peaks. The purposes of this study were 1) to examine systematically signals from sub-components of the LDI retinal/choroidal waveform in humans to maximize accuracy and reliability of AL measurements, and 2) to exploit the multiple peaks for quantitative retinal/choroidal analysis. Methods:Multiple LDI signal waveforms from 60 human subjects (4512 waveforms in total) were examined. Signal processing, statistical and heurisitic approaches were combined to create a means to identify and quantify sub-components of the LDI waveform. Results:LDI signals varied significantly between subjects and to a lesser degree between repeat measurements in the same subject. Averaging greatly enhanced signal quality. Four distinct components (p1-p4) of the LDI signal waveform were identifiable in averaged waveforms and could be identified by a rule-based algorithm (p1, 33/60 subjects; p2 58/60 subjects; p3 60/60 subjects and p4 56/60 subjects). Mean interpeak distances were p1-p3 203.9 microns (s.e.m. 10.5), p2-p3 35.9 microns (s.e.m. 2.39), p3-p4 346.4 microns (s.e.m. 33.89). Overall algorithmic identification of the most consistent peak, p3 lead to a marked improvement of repeat measure reliability as compared to maximal peak identification with a reduction of mean s.e.m. for peak 3 (thought to represent RPE/Bruchs) from 25.6 microns to 10.1 microns. Of the 54 subjects with repeat peak 3 estimations, 4 display high variance due to inconsistent automated peak identification. Within the remaining 50 subjects the mean s.e.m for automated peak 3 estimates was 4.3 microns. Conclusion:Digital waveform analysis and algorithmic peak identification significantly improves the statistical reliability of LDI measurements, sub-component analysis can provide accurate information on retino-choroidal laminar dimensions.
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