Abstract
In this paper, we propose a new procedure to robustly determine the eyelid position in high-speed videokeratoscopic images. This knowledge is crucial in videokeratoscopy to study the effects of the eyelids on the cornea and on the tear film dynamics. Difficulties arise due to the very low contrast of videokeratoscopic images and because of the occlusions caused by the eyelashes. The proposed procedure uses robust M-estimation to fit a parametric model to a set of eyelid edge candidate pixels. To detect these pixels, firstly, nonlinear image filtering operations are performed to remove the eyelashes. Secondly, we propose an image segmentation approach based on morphological operations and active contours to provide the set of candidate pixels. Subsequently, a verification procedure reduces this set to pixels that are likely to contribute to an accurate fit of the eyelid edge. We propose a complete framework, for which each stage is evaluated using real-world videokeratoscopic images. This methodology allows for automatic localization of the eyelid edges and is applicable to replace the currently used time-consuming manual labeling approach, while maintaining its accuracy.
Highlights
A keratoscope is an ophthalmological instrument that allows for non-invasive imaging of the topography of the human cornea, which is the outer surface of the eye [1]
We propose to use robust M-estimation to fit a parametric model to a set of eyelid edge candidate pixels
After applying nonlinear image filters to the initial videokeratoscopic image, an active contours image segmentation method is presented to detect pixels in videokeratoscopic images that lie on the eyelid edge. This method outperformed other image segmentation approaches, such as region growing [19], watershed segmentation [20], and empirical and gradient-based methods [16] we studied before, but we do not report for space considerations
Summary
A keratoscope is an ophthalmological instrument that allows for non-invasive imaging of the topography of the human cornea, which is the outer surface of the eye [1]. Videokeratoscopy allows for studying the dynamics of the corneal topography [2,3,4,5]. Another important application of videokeratoscopy is the analysis of tear film stability in the inter-blink interval. Videokeratoscopy is involved in the study of the dynamic response of the corneal anterior surface to mechanical forces. These mechanical forces are exerted by the eyelids during horizontal eye movements in a Figure 1 displays the principle of videokeratoscopy. Spaced symmetric reflections from the corneal surface would indicate perfect vision, while distortions in the ring pattern represent aberrations
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