A prototype xeroscope for the noninvasive measurement of tear-breakup time

James Edward D. Herrera, MD Ruben Lim Bon Siong, MD

To develop a noninvasive method for measuring tear-breakup time (TBUT) using readily available materials.

A prototype xeroscope was made using acetate with concentric rings printed on it, and cut to a diameter of 3.6 cm. The cut-out was attached to the front of an ordinary flashlight and reflected onto the patient’s cornea. Viewed through a slitlamp, the interval between a complete blink and the appearance of randomly distributed progressive distortion on the concentric rings was measured in seconds and designated as noninvasive breakup time (NIBUT). The standard method of using fluorescein dye for TBUT evaluation was performed for comparison. The prototype was tested on 50 adult patients who had no apparent ocular pathology except error of refraction and cataract. Measurement of NIBUT was done for both eyes followed by TBUT. Results were subjected to linear-regression analysis.

A total of 50 subjects (100 eyes) were included in the study. The mean NIBUT was 24.25 seconds and 25.20 seconds for the right and left eyes respectively. The mean TBUT was 18.23 seconds and 18.96 seconds for the right and left eyes respectively. Taken together, the mean NIBUT for both eyes was 24.71 seconds (range 9.44 to 49.03); and the mean TBUT was 18.63 seconds (range 4.28 to 41.65). The mean difference between NIBUT and TBUT was 6.09 seconds. There was a linear correlation between NIBUT and TBUT for both the right and left eyes. There was also a significant correlation between the right and left eyes for both NIBUT alone and TBUT alone. Regression correlation analysis revealed that TBUT is positively correlated with NIBUT (r = 0.994, p < 0.0001).

NIBUT measurement using the prototype xeroscope has a positive correlation with the standard TBUT measurement and may be a good alternative for measuring tear-film stability without disturbing normal physiology.

Keywords: Tear-breakup time, Tear film, Lacrimal glands, Xeroscope