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János Németh, Béla Erdélyi, Béla Csákány, Péter Gáspár, Alexandros Soumelidis, Ferenc Kahlesz, Zsolt Lang; High-Speed Videotopographic Measurement of Tear Film Build-up Time. Invest. Ophthalmol. Vis. Sci. 2002;43(6):1783-1790.
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purpose. To detect tear film regularity changes in the 15 seconds after a blink, by using a new high-speed videotopographic method.
methods. The new system, based on a standard corneal topograph, allows registration of four photokeratoscopic images per second. Altogether, 15 eyes of 15 healthy volunteers and 7 eyes of 7 patients with dry eye were examined in this prospective preliminary study. The main outcome measures were changes in surface regularity index (SRI), surface asymmetry index (SAI), and corneal power.
results. The corneal surface became more regular in the first few seconds after a blink. In healthy eyes, the trend line of SRI and SAI decreased (improved) significantly (P < 0.001) after a blink, in 10 of 15 eyes for the SRI and in 13 of 15 for the SAI. In the typical cases, the trend line for SRI reached its minimum level, on average, at 7.1 ± 3.9 seconds after a blink and that for the SAI at 5.4 ± 2.7 seconds. Similar trends were found in the dry-eye group. The changes in keratometric measures were small (mean range, <1.5% of the absolute value) and showed no definite trends.
conclusions. High-speed videotopography provides the possibility of quantitative measurement of tear-film dynamics and may have clinical value in the management of ocular surface disorders. After a blink, it takes the tear film approximately 3 to 10 seconds (tear film build-up time) to reach the most regular state. However, despite surface-regularity changes, the measured corneal powers are stable.
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