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High-speed videotopographic measurement of tear film build-up time
János Németh1, Béla Erdélyi, Béla Csákány
1First Department of Ophthalmology, Semmelweis University, Budapest, Hungary. nj@szem1.sote.hu
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.
