Agreement and repeatability of four different devices to measure non-invasive tear breakup time (NIBUT)

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Abstract

Purpose

Since tear film stability can be affected by fluorescein, the Dry Eye Workshop (DEWSII) recommended non-invasive measurement of tear breakup time (NIBUT). The aim of this study was to investigate the agreement and repeatability of four different instruments in the measurement of NIBUT.

Methods

72 participants (mean 24.2 ± 3.6 years) were recruited for this multi-centre, cross-sectional study. NIBUT was measured three times from one eye using each of the instruments in randomized order on two separate sessions during a day, separated by at least 2 h. NIBUT was performed at three sites (Switzerland, Germany and UK) using three subjective instruments, Tearscope Plus (Keeler, Windsor, UK) (TS), Polaris (bon Optic, Lübeck, Germany) (POL), EasyTear Viewplus (Easytear, Rovereto, Italy) (ET) and the objective Keratograph 5 M (Oculus Optikgeräte GmbH, Wetzlar, Germany) (KER). As the latter instrument only analyses for 24 s, all data was capped at this value.

Results

NIBUT measurements (average of both sessions) between the four instruments were not statistically significantly different: TS (median 10.4, range 2.0–24.0 s), POL (10.1, 1.0–24.0 s), ET (10.6, 1.0–24.0 s) and KER (11.1, 2.6–24.0 s) (p = 0.949). The objective KER measures were on average (1.2 s ± 9.6 s, 95 % confidence interval) greater than the subjective evaluations of NIBUT with the other instruments (mean difference 0.4 s ± 7.7 s, 95 % confidence interval), resulting in a higher limits of agreement. The slope was -0.08 to 0.11 indicating no bias in the difference between instruments with the magnitude of the NIBUT. Repeated measurements from the two sessions were not significantly different for TS (p = 0.584), POL (p = 0.549), ET (p = 0.701) or KER (p = 0.261).

Conclusions

The four instruments evaluated for their measurement of tear stability were reasonably repeatable and give similar average results.

Introduction

A stable pre-corneal tear film is essential to create a protective and lubricated environment for the tissues of the palpebral and bulbar surfaces and to provide the primary refracting surface for light entering the visual system [1]. Impaired tear film stability is one of the fundamental diagnostic criteria for diagnosing a loss of homeostasis of the tear film in dry eye disease and many ways of evaluating tear film stability have been described [2]. Tear film stability can be evaluated invasively by fluorescein breakup time (BUT) and non-invasively by projecting a grid or other pattern onto the tear film (NIBUT). The time interval following a complete blink to the first occurrence of breaks or a change in the reflected grid image is defined as the breakup time [3]. While the values of BUT are dependent on the amount, concentration, pH, drop size, presence of preservatives and the type of fluorescein used, the NIBUT method eliminates the physical disturbance of the tear film [[4], [5], [6]]. Furthermore, BUT can be affected by uneven tear mixing, illumination techniques and by inducing reflex tearing [5,[7], [8], [9], [10]]. Depending on the quantity of instilled fluorescein, the BUT cut-off values for dry eye have been reported to be ≤5 s for micro-quantities and ≤10 s for larger quantities of fluorescein [[11], [12], [13]].

NIBUT is recommended by the Dry Eye Workshop (DEWS ll), with a cut off of ≥10 s for normal values, using subjective methods [2]. Recently two new handheld instruments, similar to the well established, but no longer commercially available Keeler Tearscope Plus (Keeler Ltd, Windsor, UK) and video topographers equipped with additional software for objective analysis of placido ring distortion, have been launched [14].

Consequently, the aim of this multicentre study was to investigate the agreement of four different instruments in the measurement of non-invasive tear film breakup time (NIBUT) and to propose guidelines for applying the measurements to the diagnosis of dry eye disease.

Section snippets

Participants

Seventy-two participants (twenty-four per site) with a mean age of 24.2 ± 3.6 (SD) years (54 females) were recruited at three test sites at Aston University, Birmingham, UK; School of Optometry (HFAK) Cologne, Germany and University of Applied Sciences (FHNW), Olten, Switzerland. 37 participants were largely asymptomatic (OSDI < 13), 17 had mild (OSDI 13-22), 16 had moderate (OSDI 23-32) and 2 participants had severe symptoms (OSDI ≥ 33). A range of symptomology was required to assess the

Results

The descriptive data are summarised in Table 1 (median and ranges for NIBUT and OSDI), as well as in Fig. 2 (Boxplots for NIBUT median values). The Bland-Altman plots of the difference compared to the mean for each individual with each instrument combination are shown in Fig. 3. The objective Keratograph measures were on average (1.2 s ± 9.6 s 95 % confidence interval) greater than the subjective evaluations of NIBUT with the other instruments (mean difference 0.4 s ± 7.7 s 95 % confidence

Discussion

This prospective multicentre study reports on the use of four different devices to measure non-invasive tear breakup time (NIBUT). All of these instruments use the projection of a ring grid pattern to visualise the break-up of the tear film. The comparison of the handheld or slit-lamp mounted instruments (Tearscope Plus, Easytear, and Polaris) for subjective evaluation of NIBUT showed no significant difference between the NIBUT measurements. The NIBUT measurements (without cut-off of 24 s) for

Conclusions

NIBUT data of this study suggests that the four instruments for tear stability measurement give reasonably repeatable values that can be used interchangeably as long as objective instrument cut-offs are applied.

Declaration of Competing Interest

None.

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