Normalized ocular surface temperature models for tear film characteristics and dry eye disease evaluation

Abstract

Purpose

To construct normalized ocular surface temperature (NOST) models for different tear film characteristics and evaluate its potential in dry-eyes screening.

Methods

We included 227 right eyes of 227 patients. Tear film characteristics were categorized into 4 types according to fluorescein tear film breakup time (FTBUT) and Schirmer test results, namely type 1: FTBUT >5 s and Schirmer >5 mm; type 2: FTBUT ≤5 s and Schirmer >5 mm; type 3: FTBUT ≤5 s and Schirmer ≤5 mm; and type4: FTBUT >5 s and Schirmer ≤5 mm. Ocular surface temperature was measured by a video-thermographer. Mean temperatures of the central cornea were calculated from the videos of each frame during the 4-s blink interval. We first constructed individual NOST model for every tear characteristic. Participants were included for further analysis when their OSDI was ≥23, FTBUT ≤5 s, and Schirmer >5 mm. They were subdivided into short-BUT and short BUT with SPK subgroups according to the absence or presence of corneal fluorescein-stain. The NOST models of the normal, short-BUT and short BUT with SPK groups were separately constructed and the potential of screening analyzed via ROC curves.

Results

Each tear film type had a different NOST model. At 3 s after blinking, the order of NOST was type 4 >type 1 >type 3 >type 2. In dry-eye screening, the NOST was normal > short-BUT > short BUT with SPK. The NOST displayed a sensitivity 0.87, specificity 0.80, and AUC 0.88 for diagnosing short BUT with SPK.

Conclusion

NOST models are useful in differentiating tear film characteristics and screening dry-eyes. It alleviates the discomfort and inconvenience encountered during conventional dry-eye diagnosis.

Introduction

Dry eye disease (DED) is a chronic progressive condition associated with increased instability of the tear film, causing ocular surface damage that subsequently affects life and visual quality [[1], [2], [3], [4]]. The consensus on dry eye management is still under development because of the apparent lack of correlation between traditionally used clinical tests and patient-reported symptoms [5,6].Non-contact methods to diminish dry eye assessment variability are thus preferred [5].

The Asia Dry Eye Society (ADES) defines dry eye emphasizing on subjective symptoms and tear film instability [6]. One of the most commonly used dry eye questionnaires is the ocular surface disease index (OSDI) proposed by International Dry Eye Workshop report [5]. Because an unstable tear film is pivotal, the measurement of fluorescent tear film breakup time (FTBUT) is mandatory. The presence of superficial punctate keratopathy (SPK) is objective in the evaluation of ocular damage; and can be assessed by fluorescein [7]. However, traditional Schirmer test and/or ocular surface staining for dry eye diagnosis could induce reflex tearing, which reduces the reliability of test results. Therefore, new emerging dry eye diagnostic technologies focus mainly on non-contact measurement [5].

The anterior segment optical coherence tomography (AS-OCT) measures tear meniscus height (TMH) [8,9] and is considered a quantitative measurement of tear volume [10]. It could thus screen aqueous deficient dry eyes rapidly and noninvasively.

Tear evaporation is related to the tear film components and structure [11,12]. The higher tear production rate results in a higher evaporation rate [9,13], while a stable tear film is less likely to evaporate [[14], [15], [16]]. Cooling caused by tear film evaporation alters the ocular surface temperature [17] and an unstable tear film produces a relatively low-temperature area on the ocular surface [18]. Lower temperature area corresponding to the fluorescent tear film breakup area using a thermal graphic camera suggests that the breakup of the tear film increased the cooling rate due to tear evaporation [9,19,20]. Therefore, thermography could potentially evaluate tear film quality noninvasively [21,22].

Tear film characteristics can be divided into 4 types according to traditional FTBUT and Schirmer test value and correspond to the clinically defined dry eyes [[23], [24], [25]]. The thermographic difference of the 4 types of tears has not been studied. Moreover, the relation between ocular surface temperature and patient-reported symptoms has not been assessed. The aims of the current study were to (1) observe the changes in ocular surface temperature in different tear film characteristics and (2) determine whether ocular surface temperature can be used to evaluate short-BUT and short BUT dry eye with SPK.