A Simplified Xeroscope for the Noninvasive Measurement of Tear Break-up Time
Darien B. Gaw, MD, Bernard Gil O. Tinio, MD
Objective:
To develop and validate a noninvasive method for measuring tear break-up time (NIBUT) using readily available materials and comparing it to the standard fluorescein tear break-up time (TBUT) assessment.
Methods:
A prototype xeroscope was made from an ordinary round plastic lid. At its inner lining, a fluorescent green sticker paper printed with black circular concentric grid pattern was fixed to simulate modified placido rings on the precorneal reflection. A central rectangular cut-out measuring 2 cm x 1 cm was made into the base frame serving as the viewfinder for the device through which the precorneal grid reflection was observed. A 30-LED blue light strip was fixed in the inner rim of the lid using a double-sided adhesive tape and was powered by a multi-voltage AC-DC power adapter set at 6-volts at 350mA (2 watts). The prototype device was tested on fifty (50) patients (100 eyes), aged 21 to 65 years old, with no apparent ocular surface disorders and eyelid abnormalities. Measurement of NIBUT was done on both eyes using the prototype xeroscope followed by fluorescein TBUT measurement. The two values were compared and their correlation determined by linear-regression.
Results:
Fifty (50) patients (100 eyes) were enrolled into the study. The mean age was 48.52 years (range 21 to 62 years). The mean NIBUT for both eyes was 20.10 secs, ranging from 11.56 to 36.17 secs, and the mean TBUT was 18.70 secs, ranging from 10.20 to 30.40 secs. The mean difference between NIBUT and TBUT was 1.40 sec. Regression analysis revealed a strong positive linear correlation between the 2 measurements with a computed R-squared value of 0.9697.
Conclusion:
The noninvasive technique using the prototype device provided a good alternative approach for measuring tear film stability without disturbing normal tear physiology and dynamics at a fraction of the cost of current commercially-available xeroscopes and tearscopes.
Keywords:tear break-up time, noninvasive tear break-up time, tear film, xeroscope, tearscope, dry eye syndrome