Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Patent
1998-11-12
1999-11-09
Manuel, George
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
A61B 314
Patent
active
059800410
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to point of observation tracking devices for use, by way of example, in control systems, psychological research and other applications where information about the point of observation is useful. The invention also relates to devices for measuring eye focus.
BACKGROUND TO THE INVENTION
Various methods for tracking the point of observation, eye position, or point of gaze (which may be regarded as equivalent end-results) have been proposed but commonly these approaches suffer from complexity and consequent high cost, bulkiness or poor performance. Prior methods include attempting to track the muscular movements of the eye with mechanical transducers and various optical techniques.
The optical methods used in the prior art fall into two categories, viz, 1: tracking the position of the pupil; and 2: tracking a highlight from the cornea.
The pupil tracking systems are limited in accuracy by several factors the most important being the poor contrast between the iris and the pupil, particularly with dark coloured irises, which reduces the resolution with which a camera can define the pupil boundary. Secondly the iris commonly has an irregular dark border at the edge of the pupil which further degrades accuracy. Thirdly the relative motion of the pupil is not related to an external reference physically aligned with the user's head and so extrapolation of the pupil position to determine the point of observation yields poor repeatability.
The corneal highlight systems suffer from high degree of variation in corneal profiles both between individuals and from time to time in the same individual due to variations in eyeball pressure due to air pressure. The nature of the corneal highlight apparatus also causes further variations and poor repeatability since small changes in the relationship of the illumination source to the cornea drastically affect the position of the highlight.
Preferred embodiment of the present invention aim to obviate or overcome disadvantages of the prior art, whether referred to herein or otherwise.
SUMMARY OF THE INVENTION
According to the present invention in a first aspect, there is provided a point of observation tracking device comprising means for directing light from a holographic element to the retina of a user, and means for tracking the reflection of the light from the retina thereby to provide a signal representative of the point of observation of the eye or eyes of the user.
In this specification, unless the context requires otherwise the term light is used in its widest sense including the full range of electromagnetic wavelengths. In particular, it is not to be limited to the range of visible wavelengths.
Suitably, a source of illumination is provided to produce the light to be directed to the retina.
Suitably, the source of illumination comprises a controlled source. More suitably, it comprises a source of light outside the human visible spectrum, such as infra-red light.
The illumination source should be of equal intensity across the entire field of view of the camera. The illumination sphere or holographic diffusing optic should also have a focal angle of dispersion equal to the focal angle of the camera lens. These criteria ensure that good retro-reflection is obtained from the retina. Long wavelength light sources can be used so as substantially to eliminate night vision restrictions.
Preferably, the light directed to the retina comprises a holographic image. Suitably, the holographic image varies in focal length over space. Suitably, the holographic image comprises a plurality of lines which conveniently are regularly spaced. A suitable holographic image is a hemisphere or part thereof, typically formed from a grid of lines.
The holographic element preferably is a transmission hologram.
Suitably, the tracking means comprises a sensor and means for directing light reflected from the retina to the sensor. Conveniently, the sensor comprises an array of light sensitive devices and typically the sensor will be coupled to a data pr
REFERENCES:
patent: 4410244 (1983-10-01), Remijan
patent: 5638176 (1997-06-01), Hobbs et al.
Ferranti Technologies Limited
Manuel George
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