Optimising the methodology for assessing tear meniscus height using digital imaging.

PURPOSE: To determine the optimum method for assessing tear meniscus height using digital imaging.

METHOD: The tear meniscus of 38 participants (mean age 32.5 ± 10.6 years, 45 % male) was video recorded three times, each for a period of five seconds following two natural blinks using the Oculus Keratograph 5M, first with infrared and subsequently with visible (white) light. Still images at 0.5 s intervals from the last blink, up to 5 s, were extracted from the video recording and the lower eyelid tear meniscus height was measured using ImageJ at seven locations; immediately below pupil centre and at 1 mm, 3 mm and 6 mm, nasally and temporally. Dryness symptoms were assessed with the Ocular Surface Disease Index (OSDI) and tear film stability with non-invasive tear breakup time with the Oculus Keratograph 5M.

RESULTS

A significant difference in the tear meniscus height was measured with infrared (0.29 ± 0.08 mm) compared to white light (0.27 ± 0.08 mm; p < 0.001). Tear meniscus height increased significantly with repeated measurement (first: 0.27 ± 0.08 mm; second 0.27 ± 0.08; 0.28 ± 0.09; p = 0.005). In each case, following a significant decrease immediately after a blink, the tear meniscus height was stable between 1.0 and 2.5 s and increased thereafter (p < 0.001). A consistent tear meniscus height measurement was achieved by measuring within 1 mm of the pupil midline, but increased more peripherally (p < 0.001). Differences in height, while statistically significant, were not clinically significant except in the peripheral measurements.

CONCLUSION

Tear meniscus height should be measured in a consistent manner, either with infrared or white light. A single measurement from the top of the meniscus to the eyelid margin within 1 mm of the pupil midline, from an image captured 1.0 to 2.5 s after two blinks, is sufficient.