Objective Measures of Pre-lens Tear Film Dynamics versus Visual Responses

Ability of non-invasive tear break-up time to determine tear instability in contact lens wearers

PURPOSE

To evaluate the performance of precorneal and prelens non-invasive tear break-up time (NIBUT) measurements to determine tear instability in contact lens (CL) wearers.

METHODS

In this study, 50 eyes of 25 CL wearers were evaluated. Precorneal first and average NIBUTs and fluorescein tear break-up time (FBUT) were measured before wearing CLs in the morning. Those with FBUT less than 10 s were considered to have tear instability. After wearing CL, first and average prelens NIBUTs were measured at the 30th minute. The receiver operating characteristic (ROC) curve was analyzed to evaluate the performance of NIBUT measurements in the diagnosis of tear instability.

RESULTS

The FBUT value had a significant correlation with first and average precorneal NIBUT values (p < 0.001, r = 0.653 and p < 0.001, r = 0.628, respectively). The FBUT value had no correlation with the prelens first and average NIBUT values (p = 0.542 and p = 0.263, respectively). To understand the relationship between the precorneal and prelens NIBUT values measured by the automated method, their correlation was evaluated. There was no significant correlation between the precorneal and prelens NIBUTs (for all; p > 0.05). The area under curve (AUC) in ROC curve for the first and average precorneal NIBUTs were 0.842 (p < 0.001) and 0.810 (p < 0.001), respectively. The AUC values for the first and average prelens NIBUTs at the 30th minute of CL wear were 0.586 and 0.619, respectively (p = 0.317 and p = 0.166, respectively).

CONCLUSIONS

Precorneal NIBUT measurements may be useful in diagnosing tear instability. Prelens NIBUT values are not yet capable of adequately defining the tear film dynamics in CL wearers.

Assessment of Tear Film Using Videokeratoscopy Based on Fractal Dimension

SIGNIFICANCE

The proposed automated approach for estimating the quality of the tear film closes the gap between the manual and automated assessment, translating the high-speed videokeratoscopy technology from scientific laboratories to a clinical practice.

PURPOSE

To develop and test a new method for characterizing Tear Film Surface Quality with high-speed videokeratoscopy utilizing a fractal dimension approach.

METHODS

The regularity of the reflected pattern in high-speed videokeratoscopy (E300; Medmont) depends on tear film stability. Thus, determining tear film stability can be addressed by estimating the fractal dimension of the reflected pattern. The method is tested on 39 normal subjects. The results of the fractal dimension approach are compared with those obtained using previously proposed automated method, based on a gray-level co-occurrence matrix approach, and with subjective results obtained by two operators that were assessing the video recordings in ideal conditions.

RESULTS

Fractal dimension method was less affected by eye movements and changes in the videokeratoscopic image background than gray-level co-occurrence matrix method. Median difference of the noninvasive break-up time between manual and automated methods was 0.03 s (IQR = 4.47 s) and 0.0 s (IQR = 2.22 s) for gray-level co-occurrence matrix and fractal dimension approaches, respectively. Correlation coefficient with manual noninvasive break-up time was r = 0.86 (P < 0.001) for gray-level co-occurrence matrix approach, and r = 0.82 (P < 0.001) for fractal dimension approach. Significant statistical difference was found between noninvasive break-up measurements of manual and gray-level co-occurrence matrix method (P = 0.008).

CONCLUSIONS

The proposed method has the potential to characterize tear film dynamics in more detail compared to previous methods based on high-speed videokeratoscopy. It showed good correlation with manual assessment of tear film.