Abstract:
Autofocusing eyewear for correcting eye accommodative dysfunctions includes a pupil tracking VOG (video-oculography) 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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of priority of U.S. Provisional Application Ser. No. 62/249,817, filed Nov. 2, 2015, which is incorporated herein by reference in its entirety for all purposes. 
     
    
     BACKGROUND 
       [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 correcting 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 a 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. There are features of the eye, specifically the relative position of the pupils, 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 includes cameras and a computer controller to track the pupils and determine the depth of gaze using a technique known as video-oculography (VOG). Agurok et al dismisses the idea of using VOG parallax tracking to determine depth of gaze based on the assumption that the technology would be slow and the eyewear cumbersome and heavy. (U.S. Pat. No. 8,939,579) There is a need, therefore for a VOG parallax tracking system with a continuous focus lens and a computer controller to allow the user to focus automatically between near and far objects. 
       SUMMARY 
       [0005]    The present invention 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 VOG (video-oculography) 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 are sensitive to outside lighting and difficult to use reliably, the present system is able to look at the features of the eye itself to determine the pupil location. 
         [0006]    The invention 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 invention 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 to a single setting or to various settings 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 video-oculography system captures images of the eye using a sensor, such as a CMOS sensor. A diffuse illumination system can be present to help the camera operate in low-light conditions, and the camera and such illumination system can operate in the infrared range, so as to not interfere with the operation of the eye. 
         [0008]    The controller processes the image using a pupil-detection algorithm, such as the one described in R. Velenti, T. Gevers, “Accurate eye center location through invariant isocentric patterns”,  IEEE Trans. Pattern Analysis and Machine Intelligence , Vol. 34, No. 8, pp. 17851798, 2012 and D. Li, D. Winfield, D. Parkhurst, “Starburst: A hybrid algorithm for video based eye tracking combining feature based and model based approaches”, Proceedings of the IEEE Vision for Human Computer Interaction Workshop at CVPR, 18, 2005, or other, to produce X and Y coordinates of the pupil center, and/or the eccentricity of the pupil&#39;s image in the camera. 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, calculating the distance at which they intersect, and applying the focal power associated with that distance; or directly, by mapping pupil coordinates to focal powers. This and any other required mappings can be obtained in the calibration phase, which can either happen before the device is used, or can be incorporated in the regular usage by using 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. As used herein, an Alvarez lens is a lens in which two wave-shaped polycarbonate plates are configured to glide across each other, thus adjusting the power of the lens. The lens may also include a fixed lens, such as an astigmatism-correcting lens. 
         [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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. 
           [0014]      FIG. 1  is a schematic drawing of an embodiment of an imaging subsystem  10 , lenses subsystem  11 , illumination subsystem  12 , controller subsystem  13 , battery subsystem  14  and user&#39;s eyes, nose and head. 
           [0015]      FIG. 2  is a schematic drawing illustrating a function of the imaging subsystem  10  at two different depths of the user&#39;s gaze at point A and point B. 
           [0016]      FIG. 3  is a sequence of steps that the eyewear executes in order to detect the gaze depth and adjust the focal power of the lenses. 
           [0017]      FIG. 4  shows the detected pupil center from the image. 
           [0018]      FIG. 5  shows the result of the detection of the ellipse of the pupil. 
           [0019]      FIG. 6  is the function d that maps the depth of gaze (measured in cm from the eye) to the distance of pupil centers in the left and right eyes (measured in pixels). 
           [0020]      FIG. 7  shows a sequence of steps executed in an example calibration stage before the device is used. 
           [0021]      FIG. 8  shows a sequence of steps executed in incremental calibration. 
           [0022]      FIG. 9  is a histogram of the pixel intensities in an image of the eye made by an IR CMOS sensor. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The primary components of an embodiment of autofocusing eyewear are shown schematically in  FIG. 1 . In this diagram, there are two CMOS sensors forming the imaging subsystem  10 , two variable-power lenses forming the lenses subsystem  11 , four wide-angle 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. 
         [0024]    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  and ensures that a clear picture of the eye is available in all light conditions. 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 . 
         [0025]    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 position of the image of the pupil in the sensor uniquely determines the point A that the user is looking at. 
         [0026]    By using a process described below, the controller  13  determines the depth of the user&#39;s gaze from the positions of the pupils. 
         [0027]    The controller  13  continuously runs a loop shown on schematic diagram on  FIG. 3  from 5 to 200 times per second or in certain embodiments, about fifty times per second to determine the depth of the user&#39;s gaze and focus the lenses  11  accordingly. 
         [0028]    First, the images from the imaging subsystem  10  are processed by the controller  13  to find the centers of the pupils, and/or the eccentricities of the elliptical projections of pupils onto the CMOS sensors. Many algorithms exist for this purpose, such as the ones described in Velenti, 2012 and Li, 2005. The algorithms are combined so as to use a more precise algorithm to find the centers of the pupils (Velenti, 2012), and then switch to a different algorithm (Li, 2005) to find the parameters of the ellipses. An example output of the algorithm for finding the pupil centers shows the probability of each point being the center in  FIG. 4 .  FIG. 5  shows that the projection of the pupil is an ellipse whose eccentricity depends on the angle of the rotation of the eye. 
         [0029]    Then, these coordinates are used to obtain the viewing distance. The precision of the result varies with the complexity of the method. Our research, shown on  FIG. 6 , has shown sufficient accuracy close to the optical axis with even the simplest linear model which just matches X coordinates of the left (X l ) and right (X R ) pupils with the distance: 
         [0000]        d=d ( X   R   −Xd ) 
         [0030]    The function d, for a test user, is shown in  FIG. 6 . This function d is dependent on the eye anatomy and varies significantly from user to user. To obtain function d, we use the process of calibration. An example calibration method would be to ask the user to look at objects at predetermined distances (we used 0.4 m, 0.8 m, 1.2 cm, 1.6 m and 2 m). Pupil coordinates are sampled at these distances, and the function d is obtained by spline interpolation for each distance in between, allowing a mapping of the curve of pupil distance and gaze depth. 
         [0031]    The function d, can use a geometrical model of the eye, and use calibration data to determine parameters of the model such as eye radius, interpupilary distance and position of the eyes relative to the glasses. 
         [0032]    To focus the lenses  11 , we need to know the focal power needed by the user at each distance. In this example calibration method, we would also ask the user to enter the focal power required for each of the predetermined distances. This produces a mappings P L  and p R  of focal powers from the distance d: 
         [0000]        p   L   =P   L ( d )= h ( d ( X   R   −X   l )) 
         [0000]        PR PR ( d )  P   R ( d ( X   R   −XL )) 
         [0033]    These two steps can be combined into one, as shown on  FIG. 6 . The calibration can run once, before the eyewear is used for the first time. This would specify the functions: 
         [0000]        PL=PZXR   108     X ) 
         [0000]        P   R   =p   R ( X   R     −     ./K ) 
         [0034]    The preferred embodiment instead uses 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 p, and, improving the accuracy of the eyewear. 
         [0035]    Once the device is calibrated and the functions p i , and PR 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  does that many times in a second, and directs the lenses subsystem  11  to change the focal power to the desired corrective power. To minimize focusing jitter, an easing function is used. 
         [0036]    Since the accuracy of the pupil-finding algorithm depends on the cumulative illumination of the eye, the controller subsystem  13  also calculates the histogram of the pixel intensities of the image of the eyes captured by the imaging subsystem  10  to adjust the intensity of the illumination subsystem  12  so as to use the minimum illumination in which the eye is clearly discernible by the imaging subsystem  10 .  FIG. 9  shows a typical histogram of an IR CMOS sensor picture of the eye. The sclera is clearly visible as a peak on this histogram, and its position in the histogram is used to control illumination. 
         [0037]    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.