New method for evaluation of early phase tear clearance by anterior segment optical coherence tomography

Purpose To describe a new method of measuring early phase tear clearance by anterior segment optical coherence tomography (AS-OCT). Methods Sixty normal subjects were divided into a young group (30 subjects; 29.6 +/- 7.2years) and an elder group (30 subjects; 71.4 +/- 10.8years). AS-OCT (CASIA SS-1000, Tomey, Japan) with customized software was used to record the tear meniscus at the centre of the lower eyelid. Five microlitres of lukewarm saline solution was dropped into the lower conjunctival sac, and an image of the tear meniscus was obtained immediately and again 30seconds after natural blinking. The tear meniscus height (TMH) and tear meniscus area (TMA) were measured in the AS-OCT images, and the percentage decrease in the TMH and TMA was used as a measure of the tear clearance. Correlations between tear clearance and clinical features including degree of conjunctivochalasis, degree of protrusion of inferior lacrimal punctum, distance of lacrimal punctum from the Marx line and fluorescein clearance rates were also determined in another healthy population consisting of 30 subjects. Results The OCT tear clearance rate was 35.2 +/- 11% for TMH and 28.1 +/- 12.4% for TMA in the young group, and 12.4 +/- 7.3% and 6.2 +/- 9.1%, respectively in the elder group. The differences were significant for both the TMH (p=0.017) and the TMA (p=0.024). The OCT-determined tear clearance was positively correlated with the fluorescein clearance rate, and negatively correlated with the distance between the lacrimal punctum and Marx line, degree of conjunctivochalasis and degree of lacrimal punctum protrusion. Conclusion AS-OCT can be used as a rapid, non-invasive and quantitative method of determining the early phase tear clearance rate in a normal healthy population.