Abstract:
Continuously autofocusing eyeglass systems include focus adjustable lenses and a controller to automatically adjust focus power of the lenses to match the correction needed for each eye at the depth of gaze of a user. Focus depth is determined using an image obtained by illuminating the eyes with a structured light illumination source.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of priority of U.S. Provisional Application Ser. No. 62/249,847, filed Nov. 2, 2015, which is incorporated herein by reference in its entirety for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Presbyopia is an age-related farsightedness condition caused by a loss of elasticity in the lens of the eye. This loss of elasticity decreases an adult&#39;s ability to accommodate near objects. Children typically have the ability to accommodate 20 dioptres or focus on any object from 50 mm from their eye to infinity. Most adults, by age 50, can only accommodate 2 dioptres. This loss of ability to accommodate generally results in adults requiring some form of visual correction such as reading glasses to focus on near objects. This means that adults must wear reading glasses to accommodate near objects and then remove them to accommodate far objects. In cases where adults also require glasses to correct nearsightedness (inability to accommodate far objects) they must switch between two sets of glasses depending on the depth of their gaze. This is a cumbersome solution for coping with presbyopia as well as myopia and hyperopia. Users would benefit massively from eyewear that adjusted automatically to accommodate near and far objects without requiring manual input from the user. 
         [0003]    Several eyewear products have been developed to help adults accommodate both near and far objects using a couple different kinds of lenses. Adlens offers a pair of glasses that uses manually tunable Alvarez lenses that the user can adjust by twisting a knob on each lens. Pixeloptics developed glasses that allow the user to manually switch between two forms of correction (a farsightedness correction and a nearsightedness correction) by pressing a button. Pixeloptics also made a product that uses an accelerometer to allow the user to manually adjust between near and far prescriptions by moving their head. Eyejusters also produced eyewear that allows the user to manually focus Alvarez lenses. Adlens developed eyewear with a membrane lens for continuous focus accommodation that also requires the user to manually adjust a knob on the glasses in order to focus on near or far objects. None of these technologies allows for automatic continuous focus adjustment, but instead rely on user to engage the focus mechanism. 
         [0004]    In order for eyewear to make automatic adjustments to a continuous focus lens, it needs to observe the eye and determine the depth of the user&#39;s gaze. The relative positions of the pupils are examples of features of the eye that can be used to determine depth of gaze. Sorensen proposed using a neural network to process reflections from the eye to provide an at least partially in focus image in a display screen. (U.S. Pat. No. 5,861,936) The current disclosure uses cameras and a computer controller to track the pupils and determine the depth of gaze using a technique known as structured light. Gersten proposed the use of structured light to display the edge of the pupil on a corneal topography map. (U.S. Pat. No. 5,214,456) Raffle et al suggests that structured light could be used to detect the direction of someone&#39;s gaze in their Google Glass application. (U.S. Pat. No. 8,955,973). The current disclosure is not concerned with the direction of the user&#39;s gaze, instead it uses structured light to determine the depth of the user&#39;s gaze by comparing structured light scans of both eyes numerous times per second. 
       SUMMARY OF THE INVENTION 
       [0005]    The present disclosure is related to autofocusing eyewear for correcting eye accommodative dysfunctions including, but not limited to, presbyopia, myopia, hyperopia, astigmatism and asthenopia. The eyewear comprises a pupil-tracking structured-light system to determine location of the pupils, a focus-tunable lens and a controller to focus the lens based on the position of the pupils. Whereas prior-art gaze-tracking systems used Purkinje points, (U.S. Pat. No. 8,939,579), which depend on the parameters of the eye that need to be calibrated, the present system is able to look at the features of the eyes themselves to determine the position of the eyes in 3D space and therefore the point at which the eyes converge. 
         [0006]    The disclosure helps the conditions where the person needs different focal power (for each eye) for looking at the various distances. For instance, for presbyopia, the correction of the lens is the strongest for short distances. For asthenopia, the user might choose to help the muscles in their eye by doing some correction when looking at short distances for a long while. The disclosure can also be used as traditional glasses and provide a single corrective power, and use the calibration mechanism to customize the degree of correction either once or based on some other input, such as the time of day, or an input provided remotely to the eyewear by a nearby device. 
         [0007]    The structured-light system works by illuminating the eye in such a way that at least one pupil edge is present in the illumination. This is usually done by projecting at least one line onto the eye. The projected line is captured by the imaging sensor, such as a CMOS sensor. The projected line appears in the image as a curve due to the shape of the eye. The controller then finds the points on the edge, identified as positions in the image where the intensity makes significant change. From the location of the line in the image, the location of the illuminated part of the eye in 3D space can be calculated. Additionally, the shape of the lens in the eye can be discerned, and from it, the data about the lens&#39;s current focal distance. This data can be used to calibrate how much additional focal power the user needs. The behavior of the user&#39;s lens can also be used to detect if the current prescription is too high or too low. The imaging sensor and the illumination can operate in the infrared range, so as to not interfere with the operation of the eye. 
         [0008]    The controller processes the image to find the position and orientation of both eyes in 3D space and uses these coordinates to find the point at which the eyes converge. The controller then uses this data, together with data provided during calibration, to calculate the desired focal power for the lens. This calculation can be either done piecewise, by calculating the angles of both pupils, then uses geometrical relationships to calculate the distance at which gaze lines intersect (the actual viewing depth will depend on the location of the user&#39;s fovea centralis), and applying the focal power associated with that distance; or directly, by mapping pupil angles to focal powers. This and any other required mappings and parameters can either be discovered during device operation by looking at the lens feedback or be obtained in the calibration phase, which can either happen before the device is used, or can be incorporated in the regular usage by utilizing user feedback. 
         [0009]    The lens is any focus-tunable lens, such as an electro-mechanical lens (which use electrical motors or electroactive polymers to move or reshape solid, flexible or Alvarez lens) or liquid-crystal lens. An Alvarez lens is known in the art and refers to lenses comprised of two wave-shaped polycarbonate plates that are able to glide across one another. The power of each lens can be adjusted to the desired correction by causing the lenses to glide to the appropriate relative position. 
         [0010]    Certain exemplary embodiments utilize an elastomer-liquid lens system which makes use of an inline, transparent electroactive polymer actuator, including a passive membrane, a dielectric elastomer actuator membrane, and a clear liquid. The electroactive membrane is a transparent dielectric elastomer coated with transparent compliant electrodes on both sides. In certain embodiments the dielectric elastomer can be a commercially available acrylic elastomer and the electrodes are single walled carbon nanotube. (Shian et al.,  Optics Express,  Vol 21 No. 7, pp 8669-8676, 8 Apr. 2013) The focal length and the numerical aperture of the lens in the rest state are determined by both the refractive index of the liquid and the extent of the membrane bulging. The latter is controlled by the volume of the liquid placed in inside the cavity; more liquid reduces the focal length and increases the numerical aperture of the lens. The focal length of the lens can be designed to increase or decrease upon actuation depending on the location of the electroactive membrane, i.e., as the larger or smaller diameter membrane, respectively. 
         [0011]    Tunable focus flat liquid crystal spherical lenses can also be used in certain embodiments. An example of such a lens is a tunable-focus spherical lens using two flat substrates and inhomogeneous electric field over a homogeneous liquid crystal layer as described by Ren et al., Applied Physics Letters, Vol 84, No. 23, pp 4789-4791, 7 Jun. 2004. The top flat substrate has an imbedded spherical indium-tin-oxide electrode and the bottom has a planar ITO electrode on its inner surface. The inhomogeneous electric field generates a centrosymmetric gradient refractive index profile within the LC layer which causes the focusing behavior. The focal length of the LC lens can be tuned continuously from infinity to 0.6 m by the applied voltage. Any other appropriate lens systems known in the art are contemplated by the present disclosure. The lens of any of the described systems can also include a fixed lens, such as an astigmatism-correcting lens. 
         [0012]    In addition to auto-focusing eyeglasses, the current disclosure is also useful for screen gaze tracking to identify the position on a screen at which a person looking, virtual or augmented reality, for tracking position and/or depth of gaze, eye typing, surgical applications such as tracking eyes during surgery and medical testing for eye abnormalities and prescription determination, among others that would be apparent to persons of skill in this art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic drawing of the current disclosure comprising: imaging subsystem  10 , lenses subsystem  11 , illumination subsystem  12 , controller subsystem  13 , battery subsystem  14  and user&#39;s eyes, nose and head. 
           [0014]      FIG. 2  is a schematic drawing illustrating the function of the imaging subsystem  10  at two different depths of the user&#39;s gaze at point A and point B. 
           [0015]      FIG. 3  is the sequence of steps that the eyewear executes in order to detect the gaze depth and adjust the focal power of the lenses. 
           [0016]      FIG. 4  shows the sequence of steps executed in an example calibration stage before the device can be used. 
           [0017]      FIG. 5  shows the sequence of steps executed in incremental calibration. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]      FIG. 1  a schematics diagram showing the various components of the autofocusing eyewear. In this diagram, there are two CMOS sensors forming the imaging subsystem  10 , two variable-power lenses forming the lenses subsystem  11 , two IR LED lights forming the illumination subsystem  12 , controller electronics forming the controller subsystem  13  and the battery subsystem  14  which powers all the other subsystems. These subsystems  10 ,  11 ,  12 ,  13  and  14  are all mounted on an eyeglass frame. 
         [0019]    The imaging subsystem  10  is connected to the controller subsystem  13  and provides the image of the eye to be used for determining the depth of gaze. The lens subsystem  11  is connected to and controlled by the controller subsystem  13  and its role is to change the focus of the lens subsystem  11  in accordance with user&#39;s depth of gaze. The illumination subsystem  12  is connected to and controlled by the controller subsystem  13 . The controller subsystem  13  is responsible for processing the imaging subsystem  10  inputs and controlling the lenses subsystem  11  and illumination subsystem  12 . The battery subsystem  14  is connected to all the other subsystems  10 ,  11 ,  12  and  13 . 
         [0020]    The method of operation is based on the following observation. When the user looks at a point A, the eyes rotate so that the two lines originating in each eye&#39;s fovea centralis and going through the pupils intersect at that point A.  FIG. 2  shows that the angle of the eyes uniquely determines the point A that the user is looking at. Also shown on  FIG. 2  is the fact that the eye is not a perfect sphere, but has a deformation where the pupil is. By imaging the surface of the eye, both the parameters of the sphere (namely the center of the eye) and the location of the pupil can be determined. 
         [0021]    The controller  13  continuously runs a loop shown on schematic diagram on  FIG. 3  fifty times per second to determine the depth of the user&#39;s gaze and focus the lenses  11  accordingly. 
         [0022]    To focus the lenses  11 , one needs to know the focal power needed by the user at each distance. In this example calibration method, one would also ask the user to enter the focal power required for each of the predetermined distances. This produces a mappings h and p R  of focal powers from the distance d: 
         [0000]      Pi, PL(d) 
         [0000]      PR PR ( d ) 
         [0023]    Certain embodiment can also use incremental calibration. The autofocusing eyewear has a BLUETOOTH® connection which is used with a smartphone or a computer to initiate calibration mode. Whenever the user sees an object that is not in focus, the user enters the calibration mode. In this mode, the device follows the steps listed in  FIG. 8 . The user looks at the object that is not in focus, and uses the smartphone or the computer to adjust the correction for the left and right eye until the object is in focus. This adds a point in each of the mappings h and p R , improving the accuracy of the eyewear. 
         [0024]    Once the device is calibrated and the functions p L  and p R  are known, the device is able to plug in the values for the pupil location and obtain the desired corrective power for each lens  11  for the depth of user&#39;s current gaze. The controller subsystem  13  repeats the process many times per second, and directs the lenses subsystem  11  to change the focal power to the desired corrective power. In certain embodiments an easing function is used to minimize focusing jitter. 
         [0025]    Yet another embodiment can calibrate without user input by using the data about the lenses&#39; thickness which is obtained by 3D imaging of the eye. When the device detects that the user&#39;s lenses in the eye are growing in thickness and thereby increasing the prescription it can be deduced that the current prescription is not enough, and the device updates its parameters to add more focal power at the given distance. Similarly, when the device detects that the lenses are shrinking in thickness, the device updates the parameters to add less focal power at that distance. This embodiment can self-calibrate and function without any user interaction. 
         [0026]    All of the apparatus, components and methods disclosed and claimed herein can be made and used without undue experimentation in light of the present disclosure. While the apparatus, components and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the construction or components described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.