To investigate the effect of non-invasive tear stability assessment with forced eye opening on the lower tear meniscus.
Twenty-three eyes of 23 patients with aqueous-deficient dry eye and 23 eyes of 23 normal subjects were enrolled. All subjects underwent imaging with a Keratograph 5M equipped with a modified tear film scanning function. Lower tear meniscus images were captured, and tear meniscus height (TMH) was measured with an integrated ruler before and after non-invasive Keratograph break-up time (NIKBUT) measurements in each subject. Subjects were instructed to keep their eyes open as long as possible during NIKBUT measurements, and the recording was discontinued at the next blink.
The TMH values of the normal and dry eye groups were 0.20±0.05 mm and 0.14±0.03 mm, respectively, at baseline. The TMH values of dry eyes were significantly smaller than those of normal eyes (p<0.001). Significant increases in TMH values were observed in both normal (0.10±0.12 mm) and dry eyes (0.04±0.09 mm) with the NIKBUT measurement (p<0.001, p=0.039). A moderate negative correlation was observed between increased TMH and baseline TMH in dry eyes (r=-0.44, p=0.03), whereas no correlation was observed in normal eyes (r=0.04, p=0.85).
Forced eye opening required for the non-invasive tear stability assessment influences the TMH measurement possibly due to reflex tear secretion, even in patients with aqueous-deficient dry eye. TMH should be assessed before tests that require forced eye opening.