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S. Koh, C. Tung, J. V. Aquavella, G. Yoon; Simultaneous Measurement of Tear Film Dynamics Using Optical Coherence Tomography and Wavefront Sensor. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1230.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate tear film dynamics under normal noninvasive condition by measuring changes in ocular aberrations and lower tear meniscus simultaneously.
Seven normal eyes and five dry eyes with tear film break-up time shorter than 5 seconds (SBUT dry eye) were enrolled. A custom-developed high-resolution Shack-Hartmann wavefront sensor and an anterior segment optical coherence tomography (OCT) (Visante, Zeiss, Germany) were combined and used to perform simultaneous measurements of the wavefront aberration and lower tear meniscus. During the measurement, the subjects were instructed to blink every 6 seconds for a total of 30 seconds. From the measured aberration, root mean square (RMS) wavefront error and volume modulation transfer function (vMTF) induced by changes in tear film dynamics were calculated for a 5 mm pupil. Lower tear meniscus height (TMH) and area (TMA) were estimated from the cross sectional OCT images of lower tear meniscus. Tear dynamics were quantified by calculating a slope of the time course changes in RMS, vMTF, TMH and TMA between blinks.
In the normal group, RMS showed positive correlation with TMH (r=0.189, p<0.001) and with TMA (r=0.21, p<0.001). Similar correlation was found in SBUT dry eyes. TMH and TMA increased with time between the blinks. The rates of the increase in TMH were 19.7 ± 9.8 µm/sec and 9.5 ± 5.7 µm/sec for the normal and SBUT dry eye groups, respectively. For TMA, the rates were 3886 ± 2599 µm2/sec and 1460 ± 713 µm2/sec. Optical quality degraded over time between the blinks (RMS: normal 0.013 ± 0.009 µm and SBUT dry eye 0.02 ± 0.01 µm; vMTF: normal -0.22 ± 0.83 and SBUT dry eye -0.40 ± 0.07). A rate of degradation of vMTF was significantly faster in SBUT dry eyes than in normals (p=0.004), although other parameters showed no statistical differences between the groups.
Correlations between lower tear meniscus dimensions and wavefront aberrations suggest that tear dynamics may be influenced by the lower tear meniscus. Simultaneous wavefront and tear meniscus measurement has potential to provide objective differentiation between normal and dry eyes.
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