  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 which
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 non-invasive 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 non-invasive break-up time was r2 = 0.86 (p
< 0.001) for gray level co-occurrence matrix approach, and r2 = 0.82 (p <
0.001) for fractal dimension approach. Significant statistical difference was
found between non-invasive 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.
