Optimising the methodology for assessing tear meniscus height using digital imaging

Purpose: To determine the optimum digital imaging method for assessing tear meniscus height.
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 white light. Still images at 0.5s intervals from the last blink, up to 5 s, were extracted from the video recording and the lower eyelid tear meniscus height measured using ImageJ at seven locations; immediately below pupil centre and at 1mm, 3mm and 6mm, 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±0.08mm) compared to white light (0.27±0.08mm; p<0.001). Tear meniscus height increased significantly with repeated measurement (first: 0.27±0.08mm; second 0.27±0.08; 0.28±0.09; p=0.005). Following a significant decrease immediately after a blink, the tear meniscus height was stable between 1.0 and 2.5s and increased thereafter (p<0.001). A consistent tear meniscus height measurement was achieved by measuring within 1mm 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 measures consistently either with infrared or white light. A single measurement within 1mm of the pupil midline, from an image captures 1.0 to 2.5s after a blink, is sufficient.