Systems and methods for astigmatism correction in a head-mounted display

1. A method comprising:

providing, from a display device, an image to an eye of a viewer by way of a lens assembly that provides an electronically controllable cylindrical power, oriented along an electronically controllable axis, on an optical path between the display device and the eye of the viewer, wherein the lens assembly comprises:

a first liquid crystal lens providing a first electronically controllable cylindrical power, oriented along a first constant axis, in response to a first control signal; and

a second liquid crystal lens providing a second electronically controllable cylindrical power, oriented along a second constant axis that is rotationally offset from the first constant axis, in response to a second control signal;

determining, by a controller based on information indicating a cylindrical power component and a cylindrical axis component for the viewer, the first and second electronically controllable cylindrical powers that result in providing the cylindrical power component, oriented along the cylindrical axis component, for the viewer; and

generating, by the controller based on the first and second electronically controllable cylindrical powers, the first and second control signals to cause the lens assembly to provide the cylindrical power component, oriented along the cylindrical axis component, for the viewer without physical rotation of either the first liquid crystal lens or the second liquid crystal lens.

2. The method of claim 1 , wherein a rotational offset between the first constant axis and the second constant axis ranges from greater than zero degrees to less than 180 degrees.

3. The method of claim 2 , wherein the rotational offset between the first constant axis and the second constant axis is approximately 45 degrees.

4. The method of claim 2 , wherein the rotational offset between the first constant axis and the second constant axis is approximately 90 degrees.

5. The method of claim 1 , further comprising:

generating, based on further information indicating a spherical power component for the viewer, at least one second control signal to compensate for the spherical power component for the viewer; and

altering, by an actuator, a distance between the display device and the eye of the viewer based on the at least one second control signal.

6. The method of claim 1 , further comprising:

generating, based on further information indicating a spherical power component for the viewer, at least one second control signal to compensate for the spherical power component for the viewer; and

altering, by an actuator, a distance between a viewing lens and the display device based on the at least one second control signal, wherein the viewing lens is located on the optical path between the display device and the eye of the viewer.

7. The method of claim 6 , wherein the spherical power component corresponds to a sphere component of a corrective lens prescription for the viewer.

8. The method of claim 1 , further comprising:

receiving, at a manual input interface, the information indicating the cylindrical power component and the cylindrical axis component.

9. The method of claim 8 , further comprising:

storing, in a memory, the information indicating the cylindrical power component and the cylindrical axis component;

detecting, using a biometric device, a biological characteristic of the viewer;

determining, by the controller, an identity of the viewer based on the biological characteristic; and

retrieving, by the controller, the information indicating the cylindrical power component and the cylindrical axis component from the memory based on the identity of the viewer.

10. The method of claim 9 , wherein the biological characteristic comprises a characteristic of a fingerprint of the viewer.

11. The method of claim 9 , wherein the biological characteristic comprises a characteristic of an iris of the viewer.

12. The method of claim 9 , wherein the biological characteristic comprises a characteristic of a retina of the viewer.

13. The method of claim 1 , further comprising:

displaying, by the display device, test images; and

receiving, by a manual input interface, at least one first command from the viewer to alter an appearance of the test images; and

wherein generating the first and second control signals is based on the at least one first command.

14. The method of claim 13 , further comprising:

receiving, by the manual input interface, a second command from the viewer indicating a focused state for the test images; and

storing, in a memory by the controller in response to the second command, the information indicating the cylindrical power component and the cylindrical axis component for the viewer.

15. The method of claim 1 , further comprising:

detecting, by a biometric device, a biological characteristic of the viewer; and

generating, by the controller based on the biological characteristic, the information indicating the cylindrical power component and the cylindrical axis component for the viewer.

16. The method of claim 15 , wherein the biometric device comprises an optical wavefront sensor.

17. The method of claim 1 , wherein the cylindrical power component corresponds to a cylinder component of a corrective lens prescription for the viewer.

18. The method of claim 1 , wherein the cylindrical axis component corresponds to an axis component of a corrective lens prescription for the viewer.

19. A non-transitory computer-readable medium comprising:

computer-readable instructions that, when executed by at least one processor of a computing device, cause the computing device to:

provide, from a display device, an image to an eye of a viewer by way of a lens assembly that provides an electronically controllable cylindrical power, oriented along an electronically controllable axis, on an optical path between the display device and the eye of the viewer, wherein the lens assembly comprises:

a first liquid crystal lens providing a first electronically controllable cylindrical power, oriented along a first constant axis, in response to a first control signal; and

a second liquid crystal lens providing a second electronically controllable cylindrical power, oriented along a second constant axis that is rotationally offset from the first constant axis, in response to a second control signal;

determine, by a controller based on information indicating a cylindrical power component and a cylindrical axis component for the viewer, the first and second electronically controllable cylindrical powers that result in providing the cylindrical power component, oriented along the cylindrical axis component, for the viewer; and

generate, by the controller based on the first and second electronically controllable cylindrical powers, the first and second control signals to cause the lens assembly to provide the cylindrical power component, oriented along the cylindrical axis component, for the viewer without physical rotation of either the first liquid crystal lens or the second liquid crystal lens.

20. The non-transitory computer-readable medium of claim 19 , wherein the computer-readable instructions further cause the computing device to:

generate, based on further information indicating a spherical power component for the viewer, at least one second control signal to compensate for the spherical power component for the viewer; and

alter, by an actuator, a distance between at least one of the lens assembly or the display device and the eye of the viewer based on the at least one second control signal.