Relationship between and tear volume and tear meniscus curvature

Objective: To investigate the relationship between tear volume and tear meniscus curvature by means of the video meniscometer. Methods: Eleven eyes of 11 patients with severe dry eye were studied (all female; mean +/-SD age, 66.2 +/- 7.7 years; 7 left eyes and 4 right eyes), each of whose puncta had been therapeutically occluded. Four instillations of balanced salt solution were given at intervals of 1 minute in each studied eye, with the concentration increasing in 5-muL steps from 5 to 20 muL. Before and after the instillation of balanced salt solution, tear meniscus changes were recorded by video meniscometer and radius of the meniscus was calculated from the printed images by means of the concave mirror formula. Results: The mean radius of the meniscus increased linearly with increased drop volume (r(2) = 0.65, P < .001), with mean +/-SD radius values of 0.24 +/- 0.08 mm at baseline and 0.48 +/- 0.13, 0.62 +/- 0.13, 0.84 +/- 0.26, and 1.00 +/- 0.32 mm after separate instillations of 5, 10, 15, and 20 muL of balanced salt solution, respectively. For each subject, a significantly different slope defining the relationship between instilled volume and meniscus radius was seen (0.016-0.063 mm/muL; mean +/-SD, 0.039 +/- 0.015 mm/muL), which was thought to depend on the difference in capacity of the fluid reservoir over the ocular surface. Conclusions: This study confirmed that the volume of instilled eyedrops is linearly related to the resulting radius of the tear meniscus, suggesting that this radius is a useful measure in monitoring the tear volume. This is likely to have implications both for dry eye diagnosis and for confirming the efficacy of punctal occlusion in this condition.