New method for viewing Krehbiel flow by polymethylmethacrylate particles suspended in fluorescein solution

To investigate the changes in the tear flow velocities caused by ageing.

Ninety-nine subjects (41 men, mean age 48.3 ± 20.7 years) were recruited from the Department of Ophthalmology of the Ehime University Hospital. None of the subjects had serious abnormalities of the external surface of the eye. The Krehbiel flow of tears was determined by 40-μm polymethylmethacrylate (PMMA) beads suspended in a fluorescein sodium solution (PPF). The movement of the beads was video recorded through a slit-lamp during normal blinking. The flow of the beads was determined with a Motion ANALYZER(®) software (KEYENCE Co., Osaka, Japan). The velocity of the beads in young age, 20-40 years, middle age, 41-60 years and old age, ≥61 years, groups was determined.

The equation describing the velocity (mm/second) of the PMMA particles as a function of age in the lower tear meniscus measured in the direction of the lacrimal punctum was Y = 2.49-0.04X, where Y = velocity and X = age (r(2) = 0.214; p < 0.0001). For the upper meniscus, the equation was Y = 4.83-0.05X (r(2) = 0.195, p < 0.0001). The average velocity was 0.70 ± 1.66 mm/second in the lower and 2.16 ± 1.93 mm/second in the upper tear meniscus (p < 0.0001). The particle velocity decreased significantly with increasing age, but no significant difference between the male and female groups except for the lower tear meniscus when all subjects were analysed.

The PPF technique is a simple method of examining Krehbiel flow of tears and may be used for evaluating functional nasolacrimal duct obstruction quantitatively.