Patent Publication Number: US-2016242643-A1

Title: Transparent Camera for Imaging the Eye

Description:
BACKGROUND OF THE INVENTION 
     
         
         
           
             1. Gaze-tracking algorithms often require an image of the front of the eye from canthus to canthus in order to locate and analyze the pupil shape and position. Cameras to provide the tracking images are located about 15 degrees off axis, out of the central view. However, this offset reduces accuracy and limits the effective tracking area. An image taken directly in front of the eye is ideal for tracking, but blocks the view. 
             2. Gaze-tracking with the pupil image is limited to about one degree accuracy, even with glint tracking. Tracking gaze by viewing the position of the foveal choroid is much more accurate, but challenging to accomplish. Many cameras designed to look inside of the eye can provide an image of the choroid using infrared light, but they also block the view. 
             3. Modern cameras that look into the eye display the image on a computer monitor. Viewing the image of the inside of one&#39;s own eye is prevented by the opacity of the camera taking the image. The ability to easily image and view the inside of one&#39;s own eye without assistance would enable low-cost self-screening for eye-health. 
             4. Fixation during long procedures such as mfERG and dark adaptation is difficult to maintain. Small, fixed light sources seem to vanish with time. Fixating on a live image of one&#39;s own optic disc provides a captivating target with targeting self-correction. Observing natural micro-saccades is relaxing, providing long term, stress-free fixation. 
           
         
       
    
     An invisible camera is needed to image the front and inside of the eye, without blocking the view. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a line-of-sight, real time image of the front and inside of the eye, which does not interfere with viewer observation. 
     It is a particular objective of the present invention to use light waves longer than 800 nanometers to illuminate the eye. 
     It is a particular objective of the present invention to use a camera that is sensitive to light waves longer than 800 nanometers. 
     It is a particular objective of the present invention to use 2 optical elements in the visual path, one to inject light into the optical path to illuminate the eye, and the other to extract enough reflected light to form an image of the eye from temporal to nasal canthus. 
     Another feature of the present invention is to use a wavelength-selective mirror as the optic in the illumination path. 
     Another feature of the present invention is to use a partially reflective beamsplitter as the optic in the image path. 
     Another feature of the present invention is to limit corneal reflex of infrared illumination light to appear as one glint, to simplify gaze-tracking algorithms that require the glint. 
     Another feature of the present invention is to apply an anti-reflective coating to the optics to maximize transmission at the desired wavelengths and minimize unwanted reflections. 
     Another feature of the present invention is to use an electronically tunable lens to focus the image, instead of mechanical focusing methods that reposition optical elements. 
     Another feature of the present invention is to provide aperture adjustment to improve image quality with bright images. 
     Another feature of the present invention is to properly locate beam dumps and non-reflective finishes to absorb unwanted light. 
     Another feature of the present invention is to illuminate the retina with visible wavelengths of light using a wavelength-selective beamsplitter in the imaging path. Sources of visible light include, but are not limited to LED&#39;s for ERG or VEP stimulation or bleaching and lasers for therapy or photocoagulation. 
     Another feature of the present invention is to vary the duration and intensity of the source of the visible wavelengths of light. 
     Another feature of the present invention is to provide an image of the choroid. 
     Another feature of the present invention is to allow the viewer to view a wall-mounted computer display. 
     Another feature of the present invention is to vary the apparent size of a wall-mounted display with turret-mounted lenses. 
     Another feature of the present invention is to provide eye tracking while the viewer is stimulated by images on the display. 
     Another feature of the present invention is to reflect bright light from the surface of the display to provide bleaching of selective areas of the viewer&#39;s photoreceptors. 
     Another feature of the present invention is to provide a microdisplay in the viewing path. 
     Another feature of the present invention is to vary the apparent size of the microdisplay in the viewing path. 
     Another feature of the present invention is to provide eye tracking while the viewer is stimulated by images on the microdisplay. 
     Another feature of the present invention is to reflect bright light from the surface of the microdisplay to provide bleaching of selective areas of the viewer&#39;s photoreceptors. 
     Another feature of the present invention is to display the viewer&#39;s own choroid image on the display or microdisplay. 
     Another feature of the present invention is to present the choroid image off axis up to 15 degrees. 
     Another feature of the present invention is to position the choroid camera off axis up to 15 degrees. 
     Another feature of the present invention is to apply filters in the display path to attenuate the visible light, or polarize or depolarize, the visible light reaching the viewer. 
     Another feature of the present invention is to provide corrective optics at the viewport. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a configuration with the front-of-the-eye camera and the microdisplay 
         FIG. 2  shows a side view of a configuration with the front-of-the-eye camera and a wall display 
         FIG. 3  shows a side view of anatomical landmarks on the eye 
         FIG. 4  shows two transparent optic elements positioned along the viewing axis 
         FIG. 5  shows the infrared light source path 
         FIG. 6  shows the glint path from the cornea 
         FIG. 7  shows the front-of-the-eye camera imaging path 
         FIG. 8  shows a representative image at the front-of-the-eye camera focal plane 
         FIG. 9  shows the video adapter block diagram 
         FIG. 10  shows the cold mirror visible light (bleach, laser) path 
         FIG. 11  shows a side view of a configuration similar to  FIG. 1 , with the front-of-the-eye camera relocated to add a choroid camera 
         FIG. 12  shows the choroid camera imaging path 
         FIG. 13  shows a representative image at the choroid camera focal plane for the configuration of  FIG. 12   
         FIG. 14  shows the viewer looking 7.5 degrees to the side 
         FIG. 15  shows a representative image at the choroid camera focal plane for the configuration of  FIG. 14   
         FIG. 16  shows a top view of the camera assembly 
         FIG. 17A  shows a top view of the configuration with the display aligned with the viewing axis and the camera assembly aligned 15 degrees from the viewing axis as applied to the left eye.  FIG. 17B  is as applied to the right eye 
         FIG. 18  shows a representative image at the choroid camera focal plane for the configuration of  FIG. 17B . 
         FIG. 19  shows the turret lens configuration to vary magnification of a wall-mounted display 
         FIG. 20  shows the viewing path to the microdisplay 
         FIG. 21A  and  FIG. 21B  show variation of the magnification of the microdisplay with position of the optical components 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Refer to  FIG. 1  for an overview. As a starting point and as part of this innovation, a light source  21  that provides infrared light from a tungsten-halogen filament supplied by regulated AC or DC current, or light emitting diodes, or a gaseous medium arc lamp, fitted with wavelength-selective filters  22  to remove visible and/or ultraviolet photons from the light spectrum, is introduced into an imaging path with a wavelength-selective mirror  13  through lens  20 . The light source is sized and driven to deliver the optimum intensity of light required by the application. 
     In a preferred embodiment, the infrared light source uses a D-shaped lens  20  in the illumination. The desired viewing area of the choroid is primarily nasal, to view the optic disc, and thus does not need to be radially symmetric. A D-shaped lens allows the illumination and imaging paths to be closer together than they would be if a circular lens of the same diameter was used. Placing the illumination path closer to the imaging path reduces the size requirement on optic  13 , as the required dimensions to maintain a specified field of view increase with distance. 
     The viewer&#39;s eye  10  is located on the horizontal optical axis before viewing port  11 . The viewer can see through both optic  12  and  13 . In  FIG. 1 , the viewer sees a microdisplay  32 , viewed through relay  31  and projection lens  30 . 
     In  FIG. 2 , the viewer sees a larger wall display  73  located further away, without  30 ,  31  and  32 . 
     The Viewer&#39;s eye  10  is represented by  FIG. 3 , illustrating the choroid  4 , retina  5 , optic disc  6  at the back of the eye. The front of the eye shows pupil  7  and cornea  8 . 
     The imaging optical path  51  and the illumination optical path  52  are parallel to each other, and perpendicular to the viewing axis  50 . Paths  51  and  52  are co-aligned with the viewing axis  50  at the viewing port  11  and at the viewer&#39;s eye  10 . Refer to  FIG. 4 . 
     In a preferred embodiment, optic  12  is a partially reflective 45-degree beamsplitter coated to minimize backside reflections in the near infrared. 
     In a preferred embodiment, optic  13  is a wavelength-selective reflector, also known as a hot mirror, transparent to visible yet reflective of infrared light. 
     In a preferred embodiment, a single 5-watt LED is used for the infrared light source  21 . Refer to  FIG. 5 . 
     Infrared light emitted by  21  and converged by  20  reflects from  13 , passes through  12  and  11  and illuminates the viewer&#39;s eye  10 . 
     Infrared radiation, longer than 800 nm, is emitted by  21  and illuminates the cornea  8  with a cone of light  61 . Refer to  FIG. 6 . The extent of  21  must be limited such that the extreme glints  62  and  63  appear as a single source. 
     Infrared light reflected from the front of the eye  10  passes back through  11  and reflects from  12 , passing through field lens  14  and relay  15  and then through filter  17  to camera  16 . Refer to  FIG. 7 . 
     In a preferred embodiment, a wavelength-selective filter  17 , transparent to infrared and opaque to visible light, is located before the camera. 
     The image of the front of the eye at the focal plane of camera  16  is represented schematically in  FIG. 8 , illustrating canthus  3  at either side, pupil  7 , and iris  9 . 
     Also and a part of this invention, to accommodate specific, oversize, inconvenient eye-tracking camera requirements, a video adapter as shown in  FIG. 9  is provided. The canthus to canthus eye image is obtained with a camera  80  suited to mounting inside of the imaging part of this invention, reproduced on a display  81  inside of an otherwise dark box, and then viewed through the air by the eye-tracking camera  82  connected to the eye-tracking computer  83 . 
     In a preferred embodiment, lenses can be positioned between the eye-tracking camera and the display to change the apparent size of the image or correct other imaging abnormalities. 
     Also and a part of this invention, a wavelength-selective beamsplitter  18 , also known as a cold-mirror, transparent to infrared light and reflecting visible light, is placed in the imaging path before the camera to introduce light from a visible source  19  towards the viewer. Refer to  FIG. 10 . 
     In a preferred embodiment, duration, intensity, and areal size on the retina of the visible light are well-controlled to produce a localized bleaching of viewer photoreceptors. 
     Also and a part of this invention is the addition of a choroid camera  40 . Refer to  FIG. 11 . 
     Infrared light reflected from the foveal choroid  4  passes out of the eye  10  and back through  11  to reflect from  12 , passing then through field lens  41  and relay  15  and then through filter  17  to camera  40 . Refer to  FIG. 12 . 
     Anatomically, the optic disc is located 15 degrees from central view.  FIG. 13  shows a representative image of the eye with the viewer looking straight ahead and the disc 15 degrees from the viewing axis. 
     In a preferred embodiment, a polarizer is positioned at optic  22  to polarize the illumination and a cross polarizer is positioned near  17  in the choroid camera  40  path to reduce the corneal reflex from the infrared light entering the eye. 
     A proper image of the front of the eye cannot be formed with the choroid field lens  41  in place. The front-of-the-eye image is extracted with an infrared beamsplitter  35  and fold mirror  36  positioned between optic  12  and lens  41 , to obtain the required view. The image of the front of the eye at the focal plane for camera  16  is formed through relay  37  and optic  38 . Refer again to  FIG. 11 . 
     In a preferred embodiment, the beamsplitter  35  is a microscope cover glass with about 4% reflectivity. 
       FIG. 14  shows one method of optic disc self-examination of the right eye. The viewer&#39;s gaze is purposely directed 7.5 degrees to the side to align the view with the image of the disc. 
       FIG. 15  is a representative image at the choroid camera focal plane for the configuration of  FIG. 14 . The disc is shown 7.5 degrees off center. 
     Also and a part of this invention is the ability to change the relative horizontal angle of the camera assembly with respect to central view.  FIG. 16  shows the camera assembly alone. 
     In a preferred embodiment, the entire vertical camera assembly can be rotated through an arc centered on the vertical axis that passes through the entrance point to the eye, for the purpose of imaging the eye from 15 degrees to the side of the viewer&#39;s central viewing axis  50 . Refer to  FIG. 17A  for the left eye and  FIG. 17B  for the right eye. The viewer is then able to comfortably observe a live image of their own disc directly in front of them. 
       FIG. 18  is a representative image at the choroid camera focal plane for the configuration of  FIG. 17A . The optic disc is centered. 
     In a preferred embodiment, when viewing a wall display  73 , lenses can be introduced between optic  13  and the display  73  to change the apparent size to the viewer. 
     In a preferred embodiment, one or more lenses  70  and  71  are mounted to a turret  72  and rotated into view as needed to change the apparent size of the display  73  to the viewer. Refer to  FIG. 19 . 
     The viewing path to the microdisplay configuration is shown in  FIG. 20 . 
     In a preferred embodiment, when viewing a microdisplay  32 , the position of lens  30  and relay  31  with respect to lens  30  vary the apparent size of the display. Refer to  FIG. 21A  and  FIG. 21B . 
     The present invention is well adapted to carry out the objective and attain the ends and advantages mentioned, as well as other ends and advantages inherent herein. While presently preferred embodiments of the invention have been given for the purpose of disclosure, numerous changes in the details of construction and arrangement of parts may be made without departing from the spirit of the invention.