Abstract |
Purpose:
The purpose of this study was to define an objective index for the evaluation of discomfort glare with the use of a camera recording the ocular area.
Methods:
In this study participated 10 subjects from 19 to 39 years old with good visual acuity and without eyeglasses. The ocular area (and mostly the distance between the eyelids) was recorded with the use of a USB camera (max frame rate: 25 fps), which was embedded in spectacles and connected to a laptop. Discomfort was induced with a 100-Watt halogen lamp placed at 50 cm distance from the participants, followed by a condenser. Five measurements were recorded for each subject at five different corneal illumination levels. The illumination levels were 250, 500, 2000, 3000 and 6000 lux at eye level. Each measurement was done with lights off and had a duration of one minute, while there was a break of one minute between the measurements. Data acquisition and analysis was performed with an algorithm, who was developed using a computational program (MATLAB R2013b) and exported information about the eyelids distance and the number of blinks per minute of each subject.
Results:
The results show that there was a strong (negative) linear correlation of eyelids distance with the level of illumination (r=-0,77, p<0,001) and the subjective rating of discomfort (r=-0,79, p<0,001). A weak (positive) linear correlation was found between the blink rate (blinks per minute) and the illumination level (r=0,35, p<0,05) and the subjective rating (r=0,47, p<0,01). Furthermore, there was a very strong (positive) linear correlation between the blink rate detected with the algorithm and the blink rate as detected from the video (r=0,95, p<0,001). A strong (positive) linear correlation was also found between the illumination level and the subjective rating (r=0,94, p<0,001).
Conclusions:
The eyelids distance was proved that decreases with the increase of illumination level and the increase of subjective rating, so it can be used as an objective index for the evaluation of discomfort glare. The blink rate was found, for most of the participants, to increase with the increase of illumination level, but the correlation with illumination level and subjective rating was not high. The algorithm developed for the study was found to have a low error in the detection of blinks.
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