Light patterns for corneal topography
Techniques are described for generating and using an illumination pattern for corneal topography. In some examples, the illumination pattern is projected over a sequence of frames, including a first frame with a first pattern of dots arranged along a two-dimensional grid, and a second frame with a second pattern of dots arranged along the two-dimensional grid. The first pattern differs from the second pattern with respect to a wavelength of light used to project one or more dots, a position of one or more dots, or both. After the illumination pattern has been determined, it can be projected over the sequence of frames and onto an eye of a user. Reflections of the illumination pattern as projected over the sequence of frames can then be used to calculate an eye model characterizing a topography of a cornea of the eye of the user.
1. A method, comprising:
determining, by one or more processors of a control unit for a head-mounted assembly, an illumination pattern to be projected over a sequence of frames onto an eye of a user wearing the head-mounted assembly, wherein:
the sequence of frames includes a first frame and a second frame;
the first frame includes a first pattern of dots;
the second frame includes a second pattern of dots;
the first pattern and the second pattern are non-rectilinear patterns configured to become substantially rectilinear approximations of one or more corresponding reference patterns when reflected off an eye-shaped surface, wherein each reference pattern comprises dots arranged according to a two-dimensional grid having straight lines that define rows and columns in which the dots are arranged, and wherein each non-rectilinear pattern represents a transformation of a corresponding reference pattern to distort the lines of the two-dimensional grid; and
the first pattern differs from the second pattern with respect to a wavelength of light used to project one or more dots, a position of one or more dots, or both;
after determining the illumination pattern, causing, by the control unit, one or more illuminators in the head-mounted assembly to project the illumination pattern over the sequence of frames and onto the eye of the user; and
calculating, by the one or more processors, an eye model based on reflections of the illumination pattern as projected over the sequence of frames and onto the eye of the user, wherein the eye model characterizes a topography of a cornea of the eye of the user.
2. The method of claim 1 , wherein the first pattern is projected using a different wavelength of light than the second pattern.
3. The method of claim 1 , wherein the illumination pattern is projected using an illuminator that operates as a single point source of light.
4. The method of claim 3 , wherein the illumination pattern is holographically projected.
5. The method of claim 1 , further comprising:
aligning, by the one or more processors, a reflected pattern to a reference pattern, the aligning comprising determining, based on a dot product of the reflected pattern and the reference pattern, an amount by which the reflected pattern is shifted relative to the reference pattern, wherein the eye model is calculated using the reflected pattern after the reflected pattern has been aligned.
6. The method of claim 5 , wherein the illumination pattern is configured such that the dot product increases as the reflected pattern becomes less shifted relative to the reference pattern.
7. The method of claim 1 , wherein some of the dots in the illumination pattern are random or pseudorandom, and wherein the illumination pattern further includes dots that form a fiducial marker.
8. The method of claim 7 , wherein the fiducial marker is a two-dimensional barcode.
9. The method of claim 1 , wherein illumination pattern comprises non-circular dots.
10. The method of claim 1 , further comprising:
switching to a lower resolution illumination pattern after calculating the eye model, wherein the lower resolution illumination pattern comprises a subset of dots in the illumination pattern or the same dots in the illumination pattern but with lower intensity; and
tracking eye movement of the user based on reflections of the lower resolution illumination pattern.
11. A control unit for a head-mounted assembly, the control unit comprising one or more processors configured to:
determine an illumination pattern to be projected over a sequence of frames onto an eye of a user wearing the head-mounted assembly, wherein:
the sequence of frames includes a first frame and a second frame;
the first frame includes a first pattern of dots;
the second frame includes a second pattern of dots;
the first pattern and the second pattern are non-rectilinear patterns configured to become substantially rectilinear approximations of one or more corresponding reference patterns when reflected off an eye-shaped surface, wherein each reference pattern comprises dots arranged according to a two-dimensional grid having straight lines that define rows and columns in which the dots are arranged, and wherein each non-rectilinear pattern represents a transformation of a corresponding reference pattern to distort the lines of the two-dimensional grid; and
the first pattern differs from the second pattern with respect to a wavelength of light used to project one or more dots, a position of one or more dots, or both;
after determining the illumination pattern, cause one or more illuminators in the head-mounted assembly to project the illumination pattern over the sequence of frames and onto the eye of the user; and
calculate an eye model based on reflections of the illumination pattern as projected over the sequence of frames and onto the eye of the user, wherein the eye model characterizes a topography of a cornea of the eye of the user.
12. The control unit of claim 11 , wherein the control unit is configured to cause the first pattern to be projected using a different wavelength of light than the second pattern.
13. The control unit of claim 11 , wherein the control unit is configured to cause the illumination pattern to be projected using an illuminator that operates as a single point source of light.
14. The control unit of claim 13 , wherein the illuminator is configured to holographically project the illumination pattern.
15. The control unit of claim 11 , wherein:
the control unit is configured to align a reflected pattern to a reference pattern;
to align the reflected pattern, the one or more processors of the control unit are configured to determine, based on a dot product of the reflected pattern and the reference pattern, an amount by which the reflected pattern is shifted relative to the reference pattern; and
the one or more processors are configured to calculate the eye model using the reflected pattern after the reflected pattern has been aligned.
16. The control unit of claim 15 , wherein the illumination pattern is configured such that the dot product increases as the reflected pattern becomes less shifted relative to the reference pattern.
17. The control unit of claim 11 , wherein some of the dots in the illumination pattern are random or pseudorandom, and wherein the illumination pattern further includes dots that form a fiducial marker.
18. The control unit of claim 17 , wherein the fiducial marker is a two-dimensional barcode.
19. The control unit of claim 11 , wherein illumination pattern comprises non-circular dots.
20. The control unit of claim 11 , wherein the control unit is further configured to:
switch to a lower resolution illumination pattern after calculating the eye model, wherein the lower resolution illumination pattern comprises a subset of dots in the illumination pattern or the same dots in the illumination pattern but with lower intensity; and
track eye movement of the user based on reflections of the lower resolution illumination pattern.