Comparison of a new portable digital meniscometer and optical coherence tomography in tear meniscus radius measurement

PURPOSE: Non-invasive measurement of tear meniscus radius (TMR) is useful in the assessment of tear volume for dry eye diagnosis. This study investigates the agreement between a new, portable, slit-lamp mounted, digital meniscometer (PDM) and optical coherence tomography (OCT) in the measurement of human TMR. METHODS: Images of the tear meniscus at the centre of the lower lid of 30 normal subjects (8M, 22F; mean age 27.5 SD ± 9.6 years) were taken using the PDM and the OCT. On the PDM and OCT images, TMR was measured using imagej 1.46b software. The meniscus on the OCT images was subdivided vertically into three equal sections and the radius calculated for each: bottom (BTMR), centre (CTMR) and top (TTMR). The relationship between PDM and OCT measurements was analysed using Spearman's rank coefficient, and differences between PDM and OCT subsection measurements were evaluated using Bland-Altman plots. RESULTS: Tear meniscus radius measured with the PDM (0.25 ± 0.06 mm) and OCT (0.29 ± 0.09 mm) was significantly correlated (r = 0.675; p < 0.001). The mean differences between TMR using the PDM and the subsections from OCT showed that TMR measured with PDM was greater for BTMR (0.07 mm; CI 0.05-0.10; p < 0.001), similar for CTMR (-0.01 mm; CI -0.04 to 0.02; p = 0.636) and steeper for TTMR (-0.07 mm; CI -0.10 to -0.04; p < 0.001). CONCLUSIONS: Portable digital meniscometer and OCT measurements of the TMR are significantly correlated, suggesting that the new PDM is a useful surrogate for OCT in this respect. The PDM appears to measure the radius of the central section of the tear meniscus