Evaluating Tear Film Quality in Normal and Midly Symptomatic Dry Eyes With a Double-Pass Method

Abstract

Purpose: : It is important the early detection of mild dry eye symptoms that could be aggravated by different treatments, for instance corneal refractive surgery. The purpose of this study is to evaluate and compare the tear film dynamics in normal healthy eyes and in eyes with mild symptoms of dry eye conditions. We applied a non-invasive method based on a double-pass instrument to characterize tear film quality.

Methods: : The measuring technique consisted in the dynamic recording of double-pass retinal images (Santamaria, Artal & Bescos, JOSAA,1987) during unforced tear film break-up by using a clinical instrument (OQAS, Visiometrics SL, Spain). A symptomatic tear film produces a degraded retinal image and higher values of ocular scattering, quantified through an Objective Scatter Index (OSI). Two types of eyes were compared: a group (n=14) with mild dry eye symptoms and an asymptomatic control group (n=18). Series of 40 consecutive double-pass retinal images were recorded every 0.5 seconds, while the subject avoids blinking. Measurements were performed under low-light conditions to naturally increase pupil diameter maximizing the area analyzed for higher sensitivity. In every patient, additional clinical tests were also performed for comparison: break-up time (BUT), Schirmer I tests and a normalized questionnaire (McMonnies).

Results: : From the temporal evolution of the OSI, it is possible to determine an objective parameter conceptually similar to BUT. This objective break-up time value (O_BUT) is set when OSI surpasses a defined threshold value as compared with the initial baseline. Symptomatic dry eyes showed larger variability of OSI over time as compared with the control eyes. In addition, the values of O_BUT were lower in the symptomatic patients and in some cases comparable to BUT estimates. Despite large individual variability, we found an average 90% OSI increase in dry eyes.

Conclusions: : We applied a new objective optical method to evaluate the quality and stability of the tear film. It is sensitive to detect mild symptoms of dry eye and to differentiate from normal cases. The procedure allows early detection and follow-up of tear-film related patient’s complaints.

Keywords: cornea: tears/tear film/dry eye • optical properties • refractive surgery: complications