Measurement of Rotational Eye Movement
It is difficult to measure rotational eye movement constantly within an error range of 1.0 degree with the conventional methods which find an eyeball rotational angle based on the contrast in the iris pattern. To solve this problem, turning our attention to the “conjunctival blood vessel ends” located on the periphery of the iris, which are not affected by the changes in pupil diameter, the author developed a new method for measuring rotational eye movement at high speed and high accuracy by enhancing the contrast in the image of the vessels on the white of the eyeball under blue light irradiation. This paper proposes the above-mentioned new method to enable a measuring system, which is not subject to the changes in pupil diameter and eyelid closure, and has been compactly-designed in terms of both software and hardware with a miniature camera. In our evaluation experiment, the images of rotational eye movements were captured, and data on the vessel end positions were obtained by both visual measurement and this system to evaluate the estimated error and processing speed. The result suggests that our proposed system is capable of measuring rotational eye movement with an average of estimated errors equal to or lower than 0.24 degrees and at a processing speed equal to or higher than 78 fps, even if the pupil diameter varies widely.
Keywords— Rotational eye movement, tracking of blood vessel images, conjunctival blood vessel ends, blue light irradiation.