Head-mounted display device with vision correction

A head-mounted display may include a display system and an optical system in a housing. The display system may have displays that produce images. Positioners may be used to move the displays relative to the eye positions of a user's eyes. An adjustable optical system may include tunable lenses such as tunable cylindrical liquid crystal lenses. The displays may be viewed through the lenses when the user's eyes are at the eye positions. A sensor may be incorporated into the head-mounted display to measure refractive errors in the user's eyes. The sensor may include waveguides and volume holograms, and a camera for gathering light that has reflected from the retinas of the user's eyes. Viewing comfort may be enhanced by adjusting display positions relative to the eye positions and/or by adjusting lens settings based on the content being presented on the display and/or measured refractive errors.

BACKGROUND

This relates generally to optical systems and, more particularly, to optical systems for head-mounted devices.

Head-mounted devices such as virtual reality glasses and augmented reality glasses use displays to generate images and use lenses to present the images to the eyes of a user.

If care is not taken, a head-mounted device may be cumbersome and tiring to wear. Optical systems for head-mounted devices may be bulky and heavy and may not be sufficiently adjustable. Extended use of a head-mounted device with this type of optical system may be uncomfortable.

SUMMARY

A head-mounted display device may include a display system and an optical system in a housing. The display system may have displays that produce images. Positioners may be used to move the displays relative to a user's eyes. The positioners may be used to adjust the horizontal separation of the displays from each other to accommodate differences in interpupillary distance between users, may be used to make vertical display location adjustments to accommodate differences in facial anatomy between users, and may be used in adjusting eye-to-display spacing to alter focus.

The optical system may include tunable lenses such as tunable cylindrical liquid crystal lenses. The displays may be viewed through the lenses. The optical system may include fixed spherical lenses that are used in conjunction with the tunable cylindrical lenses.

A sensor may be incorporated into the head-mounted device to measure refractive errors in the user's eyes. Viewing comfort may be enhanced by adjusting display position relative to the eye positions of the user's eyes and/or by adjusting lens settings based on the content being presented on the display and/or based on measured eye refractive errors. The sensor may include waveguides and volume holograms and a camera for gathering light that has reflected from the retinas of the user's eyes. Refractive errors such as farsightedness, nearsightedness, and astigmatism may be corrected by tuning the lenses and/or adjusting display positions.

DETAILED DESCRIPTION

Head-mounted devices such as head-mounted displays may be used for virtual reality and augmented reality systems. For example, a pair of virtual reality glasses that is worn on the head of a user may be used to provide a user with virtual reality content.

An illustrative system in which a head-mounted device such as a pair of virtual reality glasses is used in providing a user with virtual reality content is shown inFIG.1. As shown inFIG.1, head-mounted display10may include a display system such as display system40that creates images and may have an optical system such as optical system20through which a user (see, e.g., user's eyes46) may view the images produced by display system40in direction48.

Display system40may be based on a liquid crystal display, an organic light-emitting diode display, a display having an array of crystalline semiconductor light-emitting diode dies, a liquid-crystal-on-silicon display, a microelectromechanical systems (MEMs) display, and/or displays based on other display technologies. Separate left and right displays may be included in system40for the user's left and right eyes or a single display may span both eyes.

Visual content (e.g., image data for still and/or moving images) may be provided to display system40using control circuitry42that is mounted in head-mounted device10and/or control circuitry that is mounted outside of head-mounted device10(e.g., in an associated portable electronic device, laptop computer, or other computing equipment). Control circuitry42may include storage such as hard-disk storage, volatile and non-volatile memory, electrically programmable storage for forming a solid-state drive, and other memory. Control circuitry42may also include one or more microprocessors, microcontrollers, digital signal processors, graphics processors, baseband processors, application-specific integrated circuits, and other processing circuitry. Communications circuits in circuitry42may be used to transmit and receive data (e.g., wirelessly and/or over wired paths). Control circuitry42may use display system40to display visual content such as virtual reality content (e.g., computer-generated content associated with a virtual world), pre-recorded video for a movie or other media, or other images.

System40may include electrically controlled positioners that can be used to adjust the positions of the displays in system40. Lens system20may include tunable lenses. During operation, control circuitry42may make position adjustments to the displays in system40, may adjust the tunable lenses in lens system20, and/or may make other adjustments to the components of device10while using system40to present the user with image content.

Input-output devices44may be coupled to control circuitry42. Input-output devices44may be used to gather user input from a user, may be used to make measurements on the environment surrounding device10, may be used to provide output to a user, and/or may be used to supply output to external electronic equipment. Input-output devices44may include buttons, joysticks, keypads, keyboard keys, touch sensors, track pads, displays, touch screen displays, microphones, speakers, light-emitting diodes for providing a user with visual output, and sensors (e.g., force sensors, temperature sensors, magnetic sensor, accelerometers, gyroscopes, and/or other sensors for measuring orientation, position, and/or movement of glasses10, proximity sensors, capacitive touch sensors, strain gauges, gas sensors, pressure sensors, ambient light sensors, and/or other sensors). If desired, input-output devices44may include a sensing system that measures the eye characteristics of the user's eyes46. For example, a wavefront sensor such as a Shack-Hartmann wavefront sensor, Tscherning sensor, or a ray tracing sensor may be used to measure refractive errors in a user's eyes such as astigmatism, farsightedness, and nearsightedness. Devices44can also include cameras (digital image sensors) for capturing images of the user's surroundings, cameras for performing gaze detection operations by viewing eyes46, and/or other cameras.

FIG.2is a diagram of portions of head-mounted device10viewed in direction48ofFIG.1(along the Z axis inFIG.2). As shown inFIG.2, optical system components such as left lens20L and right lens20R and display system components such as left display40L and right display40R for device10may be mounted in a housing such as housing12. Housing12may have the shape of a frame for a pair of glasses (e.g., head-mounted device10may resemble eyeglasses), may have the shape of a helmet (e.g., head-mounted device10may form a helmet-mounted display), may have the shape of a pair of goggles, or may have any other suitable housing shape that allows housing12to be worn on the head of a user. Configurations in which housing12supports optical system20and display system40in front of a user's eyes (e.g., eyes46) as the user is viewing optical system20and display system40in direction48may sometimes be described herein as an example. If desired, housing12may have other suitable configuration.

Housing12may be formed from plastic, metal, fiber-composite materials such as carbon-fiber materials, wood and other natural materials, glass, other materials, and/or combinations of two or more of these materials. Electrically controlled positioners (e.g., computer-controlled stepper motors, piezoelectric actuators, or other computer-controlled positioning devices that are controlled by control signals from control circuitry42) can be coupled to components of device10and used in positioning these components in desired positions relative to housing12and relative to the user wearing device10. For example, positioners50X may be used to adjust the respective X-axis positions of displays40L and40R. Positioners50Y may be used to adjust the respective positions of displays40L and40R along the Y-axis ofFIG.2. The Z-axis positions of displays40L and40R (respectively, the distances of displays40L and40R to the user's left and right eyes46) may be adjusted using positioners50Z. Positioners50L (e.g., X-axis, Y-axis, Z-axis, and/or rotational positioners) may be used in adjusting the positions of lenses20L and20R. Lens properties can also be electrically tuned in response to control signals from control circuitry42. The positioners in device10may be coupled to housing12(e.g., to move the position of a component relative to housing12) and/or may be coupled to movable structures in device10(e.g., to adjust the position of one component relative to another component or relative to a movable support structure). If desired, lens20L may be coupled to display40L using fixed support structures and lens20R may be coupled to display40R using fixed support structures so that the displays and corresponding lenses move together. In other configurations, the positions of lenses20L and20R can be fixed (or adjustable) with respect to the user's eyes while the positions of displays40L and40R relative to the user's eyes can be independently adjusted using the positioners for displays40L and40R. In some arrangements, lens positioners50L may be omitted. Arrangements in which lens positioners only provide rotational positioning for lenses20L and20R may also be used.

The adjustability of the positions of displays40L and40R and/or of lenses20L and20R along the Z-axis allows images on displays40L and40R to be brought into focus for the user. Inward and outward position adjustments parallel to the X-axis allow device10to accommodate users with different interpupillary distances; each lens and panel pair (corresponding to one eye) must be adjusted together. Adjustments along the Y dimension may allow device10to accommodate differences in user head and face anatomy (e.g., to place the displays and lenses at different heights along axis Y relative to the user's eyes). Positioner operations may be controlled in response to user input. For example, control circuitry42can use the positioners ofFIG.2to make position adjustments based on button press input, touch sensor input, voice input, on-screen menu selections, and/or other user input to devices44ofFIG.1. Position adjustments (e.g., for focus tuning) can also be made by control circuitry42automatically based on measured refractive characteristics of the eyes of a user.

In addition to using lens movement and/or display movement to perform focusing operations, lenses20L and20R may be electrically tuned based on control signals from control circuitry42. Lenses20L and20R may be, for example, tunable lenses such as tunable liquid crystal lenses or other lenses that can be dynamically tuned to exhibit different focal lengths. In the example ofFIG.3, tunable lens20T (e.g., lens20L and/or lens20R) has been formed from a pair of orthogonally oriented stacked tunable cylindrical lenses. In particular, tunable lens20T has a first tunable cylindrical lens CL1and a second tunable lens CL2formed from liquid crystal lens structures. Polarizers (e.g., linear polarizers with aligned pass axes) may be placed above CL2and below CL1.

Lens20T may include substrates such as substrates52. Substrates52may be formed from clear plastic, transparent glass, or other suitable transparent material. Transparent conductive electrodes such as electrodes54,56,58, and60may be formed on substrates52. The transparent conductive electrodes may be formed from indium tin oxide or other transparent conductive material. Photolithography and etching, shadow mask patterning, or other patterning techniques may be used in patterning the electrodes into desired shapes (e.g., rings, strips, pads in an array, etc.).

With one illustrative configuration, which is shown inFIG.3, lower electrode54of tunable cylindrical lens CL1is formed from a blanket layer of transparent conductive material and upper electrode56of tunable cylindrical lens CL1is formed from patterned strips of transparent conductive material running parallel to the Y axis. Liquid crystal material62is interposed between electrode54and electrode56. The index of refraction of liquid crystal material varies as a function of applied voltage (electric field through the liquid crystal). By independently adjusting the voltages on each of electrodes56across dimension X, the index of refraction of liquid crystal material62can be adjusted under each electrode56and the focal length of cylindrical lens CL1can therefore be adjusted.

Because electrodes56run along the Y axis ofFIG.3, the elongated axis of cylindrical lens CL1also runs parallel to the Y axis. In upper tunable cylindrical lens CL2, liquid crystal material64is interposed between electrode60and electrode58. Electrode58may be a uniform layer of transparent conductive material and upper electrode60may be formed from patterned strips of transparent conductive material running parallel to the X-axis. By adjusting the voltages applied to the electrode strips of electrode60, the focal length of tunable cylindrical lens CL2may be adjusted. The electrode strips of electrode60extend along the X-axis, so the longitudinal axis of lens CL2also extends along the X axis. Because lenses CL1and CL2are perpendicular to each other, selected cylindrical lens powers in orthogonal directions may be produced through tuning of lenses CL1and CL2. Spherical lens powers may be produced by driving both CL1and CL2(electrodes in X and Y) parametrically.

FIG.4is a graph showing how the focal length of a tunable cylindrical lens (e.g., the focal length of CL1) can be adjusted. In a first configuration, a smoothly varying profile of voltages is applied to across the electrode strips of the tunable cylindrical lens, causing the index-of-refraction n for the lens to be characterized by refractive index profile66ofFIG.4. The value of refractive index n varies in a curved shape across dimension X, thereby creating a cylindrical lens from the liquid crystal material.

To tune the lens, another smoothly varying voltage profile (e.g., with a larger magnitude) may be applied to the liquid crystal material, thereby creating refractive index profile68. As these examples demonstrate, the refractive index profile of a tunable cylindrical lens can be adjusted dynamically to adjust the focal length of the lens (e.g., to have a longer focal length and weaker lens power as illustrated by profile66or to have a shorter focal length and stronger lens power as illustrated by profile68). If desired, index-of-refraction profiles of the type shown by tunable cylindrical lens index profile70ofFIG.5may be dynamically produced to implement a cylindrical lens of a desired power using a Fresnel lens configuration.

In a tunable lens configuration of the type shown by lens20T, the longitudinal axes of lenses CL1and CL2are orthogonal, allowing a cylindrical lens to be dynamically produced along either the X or Y axis. To help correct the vision of a user with astigmatism, cylindrical lens power along the X and/or Y dimensions can be controlled using lenses CL1and CL2of tunable lens20T. If desired, a tunable cylindrical lens may be rotated using a positioner. For example, lens system20may include a mechanically or electrically rotatable cylindrical tunable lens of varying power (e.g., to compensate for eye astigmatism that is not symmetrical about the X or Y axis). Configurations in which the angular orientation of lens20T is fixed and electrical tuning is used to tune lens CL1and/or lens CL2are described herein as an example.

Lens system20may include a fixed (or tunable) spherical lens in alignment with lens20L and a fixed (or tunable) spherical lens in alignment with lens20R. When a spherical lens is combined with a tunable cylindrical lens, device10may adjust tunable lenses in system20to correct the vision of a user's eye using a spherical equivalent (e.g., a combination of a spherical lens and a cylindrical lens of appropriate powers to approximate a desired aspherical lens for correcting a user's astigmatism).

If desired, a sensor that is configured to operate as an aberrometer (e.g., a Shack-Hartmann, Tscherning, or ray tracing sensor or other suitable refractive error measurement equipment) may be used by control circuitry42to automatically measure refractive errors in the user's eyes. Holographic couplers, waveguides, and other structures of the type shown inFIG.6Amay be used in forming the wavefront sensor so that the wavefront sensor can be reduced in size sufficiently to be carried in head mounted device10.

Device10may include displays such as illustrative display40ofFIG.6A. Each display40may have an array of pixels P for generating images. As described in connection withFIG.2, device10may have two displays (e.g., displays40L and40R) for providing images for the user's left and right eyes46, respectively. Only one eye46and one corresponding display40are shown in the example ofFIG.6A.

Position sensors of the type shown inFIG.2may be used in adjusting the position of display40relative to eye46so that the images are in focus and can be comfortably viewed by the user. For example, the separation between display40and eye46can be adjusted using a Z-axis positioner (as an example). Lens system20may include fixed and/or tunable lenses (e.g., a fixed and/or tunable spherical lens, tunable cylindrical lenses, etc.).

In a Shack-Hartmann sensor configuration of the type shown inFIG.6A, light source72and camera106may be used in supplying light to eye46and measuring reflected light to measure the optical properties of eye46. Light source72may produce light74at any suitable wavelength. For example, light source72may be an infrared light source such as a laser or light-emitting diode that produces near infrared light (e.g., light at 750-1400 nm, light with a wavelength of at least 700 nm, light with a wavelength of at least 750 nm, light with a wavelength of at least 800 nm, light with a wavelength of less than 1500 nm, light with a wavelength of less than 1000 nm, light with a wavelength of less than 900 nm, or light with a wavelength of less than 850 nm, etc.). Other wavelengths of light (longer infrared wavelengths, visible wavelengths, etc.) can also be used if desired.

For a light source such as a laser, objective lens75, pinhole aperture76, collimating lens80, and iris81may be used to collimate and control the beam size of light74. These optical elements make up collimation optics assembly71. Objective lens75focuses light74onto pinhole aperture76, which acts as a spatial filter that removes uneven intensity distributions in the beam. A beam with a smooth Gaussian profile emerges from pinhole aperture76. Lens80may be used to collect and collimate the spatially filtered light. Iris81may be used to control the collimated beam size. The lenses and apertures in assembly71may be fixed components, or may be be adjusted either manually or electronically in response to control signals from control circuitry42.

Light source72may be a light-emitting diode (LED)73that emits at any suitable wavelength. Because of the finite size of the LED, the beam will diverge slightly after collimation. For an LED source, collimation optics assembly71may contain different components to mitigate beam divergence after collimation.FIG.6Bshows a configuration an aspheric lens pair77A collimates the light74from LED source73. If desired, a single aspheric lens can be used for collimation instead. InFIG.6C, collimation optics assembly71may contain just an LED73and compound parabolic concentrator77B. By sitting at the focus of the hollow parabolic mirror77B, light74can be collected and collimated. Parabolic concentrator77B is advantageous in cases where the LED source73carries a large emission profile that cannot fully be captured by a simple lens. InFIG.6D, assembly71may contain a lens array pair77C and condenser lens79. The combination of two lens arrays produces uniform illumination whose beam size can be controlled by condenser lens79. If desired, a single lens array may be used instead.

Input and output couplers such as volume holograms or other holographic couplers may be used in coupling light into and out of the ends of waveguides84and94. The couplers are directional, meaning that light can enter the volume hologram in one direction. For example, input coupler82may be used to couple light74into waveguide84. Once coupled into waveguide84, this light may travel to output coupler86in direction93within waveguide84. Output coupler86may be aligned with user's eye46(e.g., output coupler86may be interposed between display40(and lens20) and the user's eye46). With this configuration, output coupler86couples light that is traveling in direction93in waveguide84out of waveguide84and towards eye46as indicated by output light88. This illuminates the user's eye with light74. After passing through the lens of eye46, light88is reflected in direction48, as indicated by reflected light90. Input coupler92couples light90into waveguide94. Couplers86and92may be tuned to the wavelength of light74and may therefore be transparent to the user as the user is viewing images on display40in direction48.

In waveguide94, light collected from input coupler92travels to output coupler83in direction96. Output coupler83couples the light exiting waveguide94that is traveling in direction96towards camera106as output light91. Output light91passes through lens98, low pass filter100(which is located at the focus of lens98and is used to filter out noise from the light), and lenslet array102. Lenslet array102may include a two-dimensional array of lenses. These lenses focus light91onto camera106(e.g., a digital image sensor) in a two-dimensional array of spots104.

The individual intensities of the spots in the two-dimensional pattern of spots104at camera106can be analyzed by control circuitry42to characterize any refractive errors present in user's eye46(e.g., astigmatism, nearsightedness, or farsightedness). With one illustrative arrangement, control circuitry42fits Zernike polynomials to the measured intensities of spots104and processes the Zernike polynomials to determine the user's eye refractive errors (e.g., a diopter value or other eyeglasses prescription information specifying optical system settings to correct the user's vision by correcting refractive errors associated with eye46). The information on the measured refractive errors can then be used by control circuitry42to adjust the position of display40relative to eye46and/or to adjust one or more tunable lenses in optical system20.

Consider, as an example, a nearsighted user with astigmatism having a right eye (OD) prescription of sphere: −3.00 diopters, cylinder: −1.50 diopters, axis: 180°. This prescription indicates that the user needs spherical and cylindrical corrections of −3.00 and −1.5 diopters, respectively. The axis value of 180° indicates the user's astigmatism correction is horizontal. In this scenario, the spherical correction can be obtained by adjusting the separation between display40and eye46with the Z-axis positioner and the cylindrical correction can be obtained by tuning the horizontally oriented tunable cylindrical lens to produce −1.5 diopters of cylindrical lens power. The user's right eye refractive errors can be independently corrected by control circuitry42based on the measured characteristics of the user's right eye.

The content that is provided to the user may contain distant images (e.g., images of mountains) and may contain foreground content (e.g., an image of a person standing 50 cm from the user). Three-dimensional content can be provided by presenting slightly different images to the user's left and right eyes with respective displays40L and40R.

Accommodation-vergence mismatch has the potential to lead to eyestrain. To minimize eyestrain, device10may perform operations that help allow the use's ciliary muscles to relax. For example, control circuitry42may periodically (e.g., every 20 minutes) present distant content (e.g., content at an apparent distance of at least 20 feet away) to the user and may direct the user to look at this distant content for a predetermined amount of time (e.g., 20 seconds). Adjustments can also be made to the diopter correction or other optical system settings associated with device10to help enhance user eye comfort. For example, device10can be calibrated during manufacturing so that control circuitry42is able to place display14and optical system20in a low-eye-strain configuration during normal operation. When calibrating device10, device10can be tested to determine the position of display40that corresponds to a virtual image at infinity focus. This calibration information may then be stored in control circuitry42.

If a user has perfect vision (no eye correction needed) and if device10is displaying distant content (e.g., content for which the user's vergence is associated with an object located at an infinite distance from the user), device10can adjust optical system20so that the extra diopter power of device10is zero. In this arrangement, the user will be able to comfortably view the distant content without eyestrain.

If, as another example, the user is nearsighted and typically needs a −1.00 diopter lens for comfortable viewing of distant images, control circuitry42can make a −1.00 diopter adjustment when distant images are presented and corresponding increased diopter changes as closer content is being presented.

If desired, eye characteristics can be sensed using a Tscherning sensor system or a ray tracing sensor system in addition to or instead of using a Shack-Hartmann sensor to measure refractive errors.

Portions of an illustrative Tscherning sensor system (Tscherning aberrometer) are shown inFIGS.7A and7B. In a Tscherning sensor system, collimated light74from a light source such as laser72or LED73is passed through a mask such as mask120. Mask120has an array of openings such as an array of circular openings in a grid pattern having rows and columns. The presence of mask120converts light74into a series of parallel beams aligned with the array of openings in mask120. These parallel beams are coupled into waveguide84and directed to eye46as light88as described in connection withFIG.6A. After passing through eye46and forming images on the user's retina, these light beams return to waveguide94as light90(FIG.6A). Waveguide94supplies light90to lens122as light91, as shown inFIG.7B. Camera106can measure the resulting array of spots of light associated with the reflected beams of light after light91passes through lens122. Control circuitry42can analyze the measurements made by camera106to characterize refractive errors for the user's eye (e.g., using Zernike polynomials).

If desired, light source72, mask120, and waveguide84may be omitted and the array of light beams that would otherwise be passing through mask120may be generated instead by presenting an array of spots on display40. Just prior to sensing the user's eyes, the user's eyes may be placed in a relaxed condition by forming an image on display40and moving this virtual target to infinity (e.g., by slowly increasing the separation between display40and eyes46until the infinity focus position has been reached and/or by tuning lenses in system20). In this type of scenario, the light spots in the array may pass from display40to eye46without being routed to eye46using waveguide84. Reflected light90may be supplied (as light91) to camera106for analysis by control circuitry42(e.g., Zernike polynomial fitting, etc.).

Portions of a ray tracing aberrometer are shown inFIGS.8A and8B. In a ray tracing system, a beam of light74from a light source such as laser72or LED73is scanned by an electrically controlled beam scanning device such as scanning mirror124(e.g., a mirror or other device controlled by control circuitry42). The scanned beam is projected on the retina of eye46by waveguide84while the intensity of light74is pulsed by laser72or LED73. This assembly forms an array of spots on the retina of eye46. As each spot is projected onto eye46in sequence, reflected light for that spot (see, e.g., light90ofFIG.6A) is directed through waveguide94to lens122as light91ofFIG.8B. After passing through lens122, camera106can capture an image of each of the spots and control circuitry42can analyze the captured image data (e.g., using Zernike polynomial fitting).

If desired, light for a ray-tracing sensing system (ray-tracing aberrometer) may be produced by forming patterns on display40after relaxing the user's eye46. For example, a circle (ring of light) or other pattern may be formed on display40. The user's eye46may be relaxed by moving the virtual target formed by the circle or other pattern to an infinity focus position before eye measurements are made. In this type of configuration, light source72, mask120, and waveguide84may be omitted. During measurements, the circular pattern of light on display40is directed onto the user's retina and reflected as reflected light90. After passing through waveguide94in direction96and exiting as light91, camera106can capture images of the circle (which may have the shape of an ellipse) for analysis by control circuitry42. The magnification of the ellipse can be used in determining the spherical portion of the user's prescription, the major and minor axis of the ellipse can be used in determining the cylindrical portion of the user's prescription, and the axis of the user's prescription can be determined from the angle of the major axis of the ellipse measured with camera106.

Illustrative operations involved in using device10are shown inFIG.9.

During the operations of block108, device10may be calibrated. For example, device10(or a representative device in a batch of devices being calibrated) can be characterized using test equipment. During testing, display40may create a test image while control circuitry42directs positioners in device10to position display40at its infinity focus location and directs lenses in lens system20to tune to their infinity focus location. An image sensor (e.g., a dummy eye) or other test sensor may be placed in the position of the user's eye while the image is displayed. Display position offsets and/or lens tuning offsets that might be needed to bring the virtual image at infinity into focus on the test sensor may then be determined and stored in device10to calibrated device10for future use by a user.

During user operations at block110, device10may be adjusted (automatically and/or manually) so that lenses20and displays40are at appropriate locations relative to the user's eyes and face (e.g., so that lenses20and displays40are separated by an appropriate distance that matches the user's interpupillary distance, so that lenses20and displays40have appropriate Y locations, etc.). After these initial adjustments have been performed, device10may use an eye sensing system (e.g., an aberrometer such as a Hartmann-Shack, Tscherning, or ray tracing sensor or other suitable refractive error measurement equipment) to measure the characteristics of a user's eye (e.g., to automatically measure refractive errors for the user's eyes and therefore determine a user's eye prescription for both the user's left and right eyes). If desired, a user may manually supply information on the user's prescription to control circuitry42using input-output devices. A user may, for example, be prompted to supply prescription values (sphere, cylinder, axis) using a touch screen, keys, voice input, etc.

During the operations of block112, control circuitry may adjust the position of display40(e.g., the separation in dimension Z of the left display from the user's left eye and the separation in dimension Z of the right display from the user's right eye) and/or may adjust tunable lenses in optical system10to bring content on display40into focus for the user while correcting for astigmatism, farsightedness, nearsightedness, and other refractive errors in the user's vision. The focus may be adjusted based on the nature of the content being displayed (e.g., based on the whether the content is distant content such as mountains in a landscape or is close-up content such as a nearby person) to minimize accommodation-vergence mismatch while taking into account user preferences and user refractive errors.

After the focus is adjusted at block112, control circuitry42may use display system40to display images for the user. While displaying the images, control circuitry42can determine whether any of the content is associated with distant objects (distant virtual objects such as computer-generated distant mountains in a landscape) or is otherwise associated with the user's relaxed eye focus state (eyes focusing at infinity). A timer may be maintained to track the amount of time elapsed between periods in which long-distance (e.g., infinity focus) content is being displayed for more than a predetermined amount of time (e.g., at least 20 seconds, at least 10 seconds, a threshold amount of time less than 2 minutes, etc.).

When the timer expires (e.g., after at least 15 minutes, at least 20 minutes, 10-30 minutes, a time period of less than 40 minutes, or other suitable time limit beyond which the user is not allowed to continue without eye relaxation), control circuitry42can conclude that it is time for the user to relax their eyes. Accordingly, content at a large distance (e.g., at infinity or greater than 20 feet away) can be presented to the user (block116). As the user views this distant content (and as control circuitry42adjust the position of display40and optical system20to their corresponding infinity focus states), the user's ciliary muscles in eyes46relax. After a suitable eye relaxation period has passed (e.g., after at least 10 s, at least 20 s, at least 30 s, at least 15-30 s, a time period less than 3 min, or other suitable relaxation time period), processing may return to block112, as indicated by line118. The eye relaxation content (long distance) content that is displayed during the operations of block116may include a message such as “relax eyes” that is presented at an infinity focus point or other suitably large distance or may include embedded content (e.g., mountains at an infinity focus or other suitable large distance) that is forced into the content that is otherwise being presented to the user. For example, a user playing a video game may be in a confined space and close to surrounding objects. To allow the user's eyes to relax during the operations of block116, a distant mountain scene may be inserted into the video game, thereby avoiding the need to interrupt the user with a text message (“relax eyes”) or other content that might disrupt the user's enjoyment of the video game.

A user of device10may not have perfect vision. For example, a user may be nearsighted, may be farsighted, and/or may have astigmatism. To correct for imperfect vision, vision correction lenses may be coupled to device10. Lenses20may, for example, have a fixed portion and a removable vision correction portion.

Vision correction lenses may, for example, have a positive diopter (to correct for farsightedness or a negative diopter (to correct for nearsightedness). Astigmatism may also be corrected. Corrective lenses that correct for astigmatism are not be rotationally symmetric. To ensure that vision correction lenses that are not rotationally symmetric are oriented properly, device10may be provided with vision correction lens orientation features (e.g., a magnetic coupling structure or mechanical coupling structure that accurately aligns the corrective lens while coupling the corrective lens to lens20L or20R in device10so that the corrective lens has a desired angular orientation with respect to device10and display40and therefore to the user's eyes when device10is being worn by the user).

An illustrative vision correction lens arrangement is shown inFIG.10. In the example ofFIG.10, vision correction lens130has been mounted within device10overlapping lens20. Lens20may be a catadioptric lens or other suitable lens. Lens20may be tunable or may be fixed. Lens130may be rotationally symmetric or may be rotationally asymmetric. As shown inFIG.10, lens130may have a convex outer surface SF3that faces lens20and may have a concave inner surface. In configurations in which lens130is rotationally asymmetric to compensate for astigmatism, the concave inner surface of lens130may be characterized by a first curvature (shown by cross-sectional profile SF1) along a first dimension (e.g., along the X axis) and may be characterized by a different second curvature (shown by cross-sectional profile SF2) along a second dimension (e.g., along the Y axis). When lens130overlaps lens20, a two-part lens is formed that is corrected to compensate for the user's vision problems.

Vision correction lens130may have a support structure such as vision correction lens mounting ring132. Lens20may be mounted in a support structure such as lens mounting structure134(e.g., a portion of a housing or other structural support in device10). Structure134may have an opening (e.g., a circular opening or an opening of other suitable shape) that receives mounting ring132. When ring132is received within structure134, alignment features associated with ring132and structure134accurately align vision correction ring132with respect to structure134(e.g., the angular orientation of ring132and therefore vision correction lens130with respect to lens20, display40, and other portions of device10is established within less than 2o, within less than 4o, or other suitable amount).

With one illustrative configuration, magnetic alignment structures may be used on ring132and structure134. As shown inFIG.11, for example, lens130may be mounted within ring132and may potentially rotate with respect to center point CP as ring132rotates within a circular opening in support structure134. To place vision correction lens130into a desired rotational alignment with respect to structure134and the rest of device10, ring132may be provided with one or more magnets such as magnets138and140and structure134may be provided with one or more corresponding magnets136and142. When vision correction lens130is mounted to device10, magnetic attraction between magnet138and magnet136and magnetic attraction between magnet140and142will help align and hold lens130in a desired angular orientation within device10, thereby ensuring that lens130satisfactorily corrects a user's astigmatism.

To ensure that a user's vision is corrected satisfactorily when using device10, vision correction lenses130may be coupled to device10in alignment with lenses20before use of device10. For example, a left vision correction lens may be coupled to device10in alignment with (overlapping) left lens20L and a right vision correction lens may be coupled to device10in alignment with right lens20R. Vision correction lenses130may be coupled to device10magnetically (e.g., using magnets and/or magnetic material), using threaded retention rings, using clips, using adhesive, and/or using other suitable mounting structures. In some configurations, vision correction lenses130are removably coupled to device10(e.g., so that a different user may replace the vision correction lenses130with a different set of vision correction lenses if desired).

When vision correction lenses130are incorporated into device10, lenses130and20operate together. For example, lenses20may serve to provide most of the optical power used in bringing display40into focus, while lenses130may correct for user-specific vision problems such as astigmatism, etc. If desired, tunable lens structures may be used in combination with vision correction lenses130and/or other fixed lenses (e.g., catadioptric lenses, Fresnel lenses, etc.).

In accordance with an embodiment, a head-mounted device configured to generate images viewable by a user having an eye with refractive errors that is located at an eye position is provided that includes a display configured to display the images, a lens through which the images are viewable, a sensor, a positioner coupled to the display, and control circuitry configured to measure the refractive errors with the sensor and configured to adjust the positioner based on the measured refractive errors.

In accordance with another embodiment, the sensor includes at least one waveguide.

In accordance with another embodiment, the sensor includes an input coupler that couples light into the waveguide and includes an output coupler that couples light out of the waveguide.

In accordance with another embodiment, the output coupler is configured to allow images to pass from the display to the eye position.

In accordance with another embodiment, the input coupler and output coupler are volume holograms.

In accordance with another embodiment, the sensor further includes a camera that measures light from the output coupler.

In accordance with another embodiment, the head-mounted device includes a light source selected from the group consisting of a laser and a light emitting diode that supplies light, an additional waveguide having an additional input coupler that couples the light into the additional waveguide and that has an additional output coupler that directs the light out of the additional waveguide towards the eye position.

In accordance with another embodiment, the head-mounted device includes a lens array interposed between the output coupler and the camera, the control circuitry is configured to measure the refractive errors by analyzing light spots produced by the lens array at the camera.

In accordance with another embodiment, the sensor is configured to form a Shack-Hartmann aberrometer.

In accordance with another embodiment, the sensor is configured to form a Tscherning aberrometer and the control circuitry is configured to measure the refractive errors by analyzing light spots at the camera that are produced while an array of dots are displayed on the display.

In accordance with another embodiment, the sensor is configured to form a ray tracing aberrometer and the control circuitry is configured to measure the refractive errors by analyzing a light pattern at the camera that is produced while a shape is displayed on the display.

In accordance with another embodiment, the shape includes a circle.

In accordance with another embodiment, the control circuitry is configured to allow the eye to relax by periodically presenting content on the display while adjusting at least a selected one of: the display and the lens to an infinity focus setting.

In accordance with another embodiment, the head-mounted device includes an input-output device, the control circuitry is configured to receive user input on the refractive errors with the input-output device.

In accordance with another embodiment, the user input includes an eyeglasses prescription and the control circuitry is configured to adjust a position of the display with the positioner based on the eyeglasses prescription.

In accordance with another embodiment, the lens includes a tunable lens and the control circuitry is configured to adjust the tunable lens based at least partly on the measured refractive errors.

In accordance with another embodiment, the tunable lens includes at least one tunable liquid crystal cylindrical lens, the measured refractive errors are associated with astigmatism in the eye, and the control circuitry is configured to adjust the tunable liquid crystal cylindrical lens based on the measured refractive errors to correct the astigmatism.

In accordance with another embodiment, the lens includes a vision correction lens.

In accordance with another embodiment, the vision correction lens is rotationally asymmetric and is configured to compensate for astigmatism.

In accordance with another embodiment, the vision correction lens is a Fresnel lens.

In accordance with another embodiment, the lens includes a fixed lens and a removable vision correction lens that is configured to overlap the fixed lens.

In accordance with another embodiment, the removable vision correction lens includes rotational alignment structures configured to rotationally align the removable vision correction lens relative to the fixed lens.

In accordance with another embodiment, the rotational alignment structures include a magnet.

In accordance with an embodiment, a head-mounted device is provided that includes a display configured to display images, a lens, a sensor that includes at least one hologram, and control circuitry configured to measure refractive errors in eyes with the sensor and configured to adjust at least one of: the lens and a position of the display based on the measured refractive errors.

In accordance with another embodiment, the sensor includes a camera, the refractive errors includes astigmatism, the lens includes an adjustable liquid crystal cylindrical lens, and the control circuitry is configured to adjust the adjustable liquid crystal cylindrical lens to correct the astigmatism as the display is viewed.

In accordance with an embodiment, a head-mounted device is provided that includes a display, a lens through which the display is viewable from an eye position, a waveguide, a hologram on the waveguide through which the display is viewable from the eye position, a camera, and control circuitry configured to measure eye refractive errors based on measurements with the camera on light exiting the waveguide.