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M. J. Collins, D. H. Szczesna, D. Alonso-Caneiro, D. R. Iskander, S. A. Read; Noninvasive Assessment of Tear Film Surface Quality. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3372.
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© ARVO (1962-2015); The Authors (2016-present)
To conduct a comparative study of three noninvasive techniques for assessing tear film surface characteristics of normal subjects during natural blinking conditions.
Eighteen healthy subjects were recruited for this study. A clinical assessment confirmed all subjects exhibited normal ocular surface and tear film characteristics. Dynamic-area high speed videokeratoscopy (HSV), dynamic wavefront sensing (DWS), and lateral shearing interferometry (LSI) were used to assess tear film surface quality (TFSQ). In HSV, temporal changes in the Placido disc pattern that is reflected from the tear surface were used as a TFSQ indicator. In DWS, temporal changes of higher order aberrations (HOA), total comatic terms (ComaV, and ComaH) and the Zernike polynomial RMS fit error were used as indicators of TFSQ. In LSI, temporal changes of the frequency characteristics of interferograms were used as a TFSQ indicator. Noninvasive measurement of TFSQ was performed in natural blinking conditions with the 18 subjects with all three techniques. A set of algorithms was used to derive tear film surface characteristics from each of the instruments. Parametric functions were used to fit the estimated tear film surface characteristics. Two parameters were estimated: the tear film build-up time (BLDT) and the average tear film surface quality in the stable phase of the interblink interval (TFSQ_Av).
The group mean BLDT across the three techniques ranged from 0.89 to 2.46 seconds, while the group median values ranged from 0.60 to 1.92 seconds. To ascertain the precision of the instruments, the average coefficient of variation for TFSQ_Av was considered. It was less than 1% for HSV, less than 3% for LSI and ranged from 1.5% to 15% for DWS. Moderate but significant correlations were found between BLDT measured with LSI and DWS based on vertical coma (Pearson’s r2=0.34, p<0.01) and higher order RMS (r2=0.31, p<0.01) as well as between TFSQ_Av measured with LSI and HSV (r2=0.35, p<0.01) and between LSI and DWS based on the RMS fit error (r2=0.40, p<0.01). No significant correlation was found between HSV and DWS.
All three techniques estimated the BLDT to be below 2.5 seconds and achieved a remarkably close median value of 0.7 seconds. HSV appears to be the most precise method for measuring tear film surface quality. LSI appeared to be the most sensitive method for analyzing the tear film build-up.
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