Eye position registering and tracking
Embodiments of the invention refer to a system for registering and tracking the position of a person's eye, in particular for refractive ophthalmic surgery. According to embodiments, the system is structured such that eye images containing at least the iris and the pupil of the eye are made at a first wavelength of light and that eye images containing scleral blood vessels are made at a different second wavelength of light. The invention furthermore refers to a corresponding method for registering and tracking the position of a person's eye.
1. A system for registering and tracking the position of a person's eye, in particular for refractive ophthalmic surgery, comprising:
a camera system for taking images of the person's eye;
storage means connected to the camera system for storing at least one eye image as a reference eye image; and
an image processing system connected to at least one of the storage means and the camera system, the image processing system structured to compare a momentary eye image with the reference eye image and to output a signal representing a change of eye position between the reference eye image and the momentary eye image,
wherein the system is structured such that eye images containing at least the iris and the pupil of the eye are made at a first wavelength of light and that eye images containing scleral blood vessels are made at a different second wavelength of light.
2. A system according to claim 1 , wherein the first wavelength lies in a wavelength range between approximately 780 nm and 950 nm and that the second wavelength lies in a wavelength range between approximately 500 nm and 580 nm.
3. A system according to claim 2 , wherein the second wavelength is set to a local maximum of an absorption spectrum of hemoglobin.
4. A system according to claim 1 wherein it comprises a first light source system illuminating the iris and the pupil of the eye and a second light source system illuminating the sclera of the eye.
5. A system according to claim 1 , wherein the first and second light source systems are controlled such as to simultaneously illuminate the respective parts of the eye.
6. A system according to claim 1 , wherein the light directing means comprise a scanning mirror and/or a movable lens.
7. A system according to claim 1 , further comprising multiplexing means for controlling the first and second light source systems for alternately illuminating the entire eye.
8. A system according to claim 7 , wherein the image processing system is structured to subtract an image which is recorded at the second wavelength of light from the second light source system from a preceding image recorded at the first wavelength of light from the first light source system.
9. A system according to claim 4 , wherein the first light source system is arranged such as to illuminate the eye at an angle of approximately 30° with respect to the visual axis.
10. A system according to claim 4 , wherein the second light source system comprises two light sources arranged such as to symmetrically illuminate the eye at angles of approximately +35° and −35°, respectively, with respect to the visual axis.
11. A system according to claim 1 , wherein the camera system is only sensitive to light of the first and the second wavelength.
12. A system according to claim 11 , wherein the camera system comprises one single camera provided with a double-passband filter.
13. A system according to claim 11 , wherein the camera system comprises a CCD camera having a combination chip with at least two separate color bands corresponding to the first and the second wavelength, respectively.
14. A system according to claim 11 , wherein the camera system comprises a first camera sensitive only to the first wavelength and a second camera sensitive only to the second wavelength.