Eye Fixation Monitor and Tracker
Apparatus and method are provided for assessing the direction of fixation of an eye by detecting polarization-related changes in light retroreflected from the fundus of the eye. Nerve fibers in the retina of the eye are birefringent and alter the polarization state of light traversing them as function of their orientation. The nerve fibers are arrayed in a characteristic pattern in the retina, specifically radiating outward from the fovea and converging to the optic nerve head. By assessment of polarization-related changes in retroreflected light from multiple retinal areas either sequentially or simultaneously characteristic birefringence signatures of portions of the retina can be identified which are used to assess the direction of fixation of the eye. In addition, using incident light having a polarization state that is substantially independent of meridional direction reduces interference from the corneal birefringence. Circularly polarized light or non-polarized light is used for the assessment. Detecting polarization-related changes that are substantially independent of the meridional direction of corneal birefringence reduces interference from the corneal birefringence still further. This is accomplished by detecting changes in ellipticity by measuring solely the Stokes parameter S3 or by measuring any two Stokes parameters. An alternative is measuring the overall intensity of the retroreflected light when the dichroism of the lutein pigment particles in the vicinity of the fovea is used for the assessment.
Patent Status: U.S. patent(s) 6,027,216 issued.
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