Patent Description:
Retinal images are broadly used for diagnosis of various diseases of the human retina. For instance, various retinal cameras have been routinely used to screen and to detect three of the most common eye diseases in adults: diabetic eye disease, glaucoma and age-related macular degeneration. Early detection of these diseases can delay and prevent subsequent loss of vision. The conventional retina cameras used to perform these screening exams typically have a central <NUM> to <NUM> degree field of view (FOV) representing less than <NUM>% of the entire surface area of the retina, but focused on the optic nerve and macula most affected by these diseases and responsible for loss of central vision.

In contrast, wide field retinal images, referring to a greater than <NUM> degree FOV, are commonly used in the diagnosis of retinopathy of prematurity (ROP), a retinal disease of pre-mature infants. At advanced stages ROP can result in retinal detachment with permanent vision loss, but is often treatable with early routine screening and detection. Traditionally, ROP is typically diagnosed via manual physician exam using an indirect ophthalmoscope. The examining physician utilizes indirect ophthalmoscopy, and relies on scleral depression to visualize the retinal periphery to the ora serrata over <NUM> cardinal positions (<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM>). Given that pathology associated with ROP occurs predominantly in the retinal periphery, a minimum <NUM> degree FOV of the retina is required for proper diagnosis. Traditional screening and diagnosis of ROP requires a highly skilled ophthalmologist to perform this exam and correctly document their retinal findings. It is a time consuming process and it lacks reliable documentation, with most ophthalmologists still performing sketched drawings to represent their retinal findings.

Wide field retinal images in a digital format can be obtained with the Retcam from Clarity Medical Systems (Pleasanton, California, United States of America). In one approach, a wide field fundus camera employs an illumination ring as shown in <CIT>) located at the tip of a hand piece housing the illumination light source, imaging optics and camera sensor. The illumination ring is formed with a bundle of optical fibers and projects bright illumination through the entire pupil. The device provides uniform illumination over a field of view to produce a retinal image with a <NUM> degree FOV of the retina. Use of such a configuration may lack clarity in the image when the crystalline lens is less transparent and when the Purkinje reflection images from the crystalline lens surfaces become visible inside the field of view. Use of such a configuration may be suitable newborn babies and infants with a highly transparent crystalline lens, but may be less suitable for patients with a less transparent lens, in particular adults.

<CIT> discloses a hand-held device for examining a patient's retina [<NUM>] comprising:.

Newborn babies and infants may have a less-transparent crystalline lens, due to various clinical conditions. Image haze may appear due to lens scattering inside a less-transparent crystalline lens wherever the illumination beam path overlaps with imaging beam path. This image haze may stem from Purkinje reflection images from crystalline lens surfaces. Image haze may be improved by separating the illumination beam path from the image beam path inside the crystalline lens. This configuration can be found in conventional retinal cameras, but with a limit on field of view of <NUM> to <NUM> degrees and with various masks on the illumination beam path to create an image window throughout the crystalline lens. However, such a configuration remains a challenge to implement for a wider field of view fundus camera.

Another highly desirable feature for fundus cameras would be a quick and reliable auto focus. Unlike conventional tabletop fundus cameras, a wide field fundus camera for ROP screening is typically a handheld device and thus fast response of the camera may improve the usability of the device. Generally, auto focus found in conventional tabletop fundus cameras is much slower than found in consumer image recording devices. There have been prior attempts to implement a consumer image recording device with fast auto focus into a handheld fundus camera.

In US patent application publication <CIT> disclose how to implement a consumer image recording device into a handheld fundus camera to utilize auto focus mechanisms built into a consumer camera. Another concern is the reliability as auto focus in consumer image recording devices may rely on well-illuminated and high contrast features to perform, while retinal images may lack such well-illuminated and high contrast features. In US patent application publication <CIT> disclose how to project a diffractively-modified laser beam to create well-illuminated and high contrast features on the retina to enhance auto focusing. A further challenge arises as to how to implement the concept with non-coherent light and how to improve performance through less-transparent crystalline lenses.

The present inventors have recognized, among other things, that auto focusing and imaging through a less-transparent crystalline lens remain challenging issues for wide field fundus cameras with a wide field of view. Meanwhile, instrumenting an indirect ophthalmoscope into a digital format and adapting a consumer image recording device and its fast auto focus have yet to be implemented for wide field fundus cameras.

The invention according to claim <NUM> includes a wide field fundus camera incorporating multiple illumination beam projectors, of which each illumination beam projector mimics the illumination conditions of an indirect ophthalmoscope.

<FIG> shows the Retcam contained on a rolling cart with a handheld imaging camera <NUM>. A computer on the cart connects to the camera sensor inside the handheld imaging camera. Halogen illumination on the cart connects via fiber optic cable to the handpiece. B The contact lens <NUM> of the handpiece is positioned on the neonate's cornea following dilation and lid speculum placement C, D Fiber optic illumination <NUM> is routed thru the lens module <NUM> to the front of the handpiece <NUM> at the sides of the imaging lens <NUM> to create ring illumination <NUM>. E Representative field of the entire retina divided into zones I, II, and III used for retinopathy of prematurity screening (ROP). Direct ring illumination may cover a <NUM> degree field of view allowing macular centered pictures to reach zone II of the retina, but requiring repositioning of the handpiece in up to <NUM> locations to fully image the entire peripheral retina in zone III to the Ora Serrata <NUM>. F Ring illumination may create a "donut" in some patients <NUM>, with illumination falling off peripherally and centrally. G Some peripheral details of retina such as a demarcation line associated with ROP (<NUM> - white arrows) may be less visible if there is insufficient peripheral illumination of the retina. H In adult patients there may be prominence of the human lens reflection (Purkinje III and IV reflection) of the ring illumination, which occurs due to changes in refractive power of the human lens following the neonatal period <NUM>.

<FIG> shows an illustrative example of a wide field fundus camera <NUM> with multiple illumination beam projectors 30a-30n and a narrow beam projector <NUM>. The wide field fundus camera <NUM> includes primarily an objective lens <NUM>, an image recording device <NUM>, a plurality of illumination beam projectors 30a-30n, a narrow beam projector <NUM>, a first polarizer <NUM> and a set of second polarizers 31a-31n. The wide field fundus camera <NUM> further includes a contact lens <NUM>, a focusing lens <NUM>, an electronic controller <NUM> and an image display <NUM>.

Objective lens <NUM> may be an aspherical lens and is located at a first end of the wide field fundus camera <NUM>. The objective lens <NUM> defines a symmetric viewing axis <NUM> and a working plane <NUM> of the wide field fundus camera <NUM>. The plurality of illumination beams 32a-32n emerging through an illumination aperture <NUM> are pre-focused at the working plane <NUM>. When a subject eye <NUM> is aligned with the wide field fundus camera <NUM> for fundus viewing, subject pupil <NUM> is about to position at the working plane <NUM> and the illumination beams 32a-32n are projected into subject pupil <NUM> to illuminate the subject retina <NUM> for alignment and for photographing. At a proper alignment, objective lens <NUM> produces a first retina image near its back focal plane <NUM>, and the first retina image is then re-imaged into the image recording device <NUM>. The illumination aperture <NUM> is located at the back focal plane <NUM> so as to define illumination area on the subject retina <NUM>.

At a proper alignment, objective lens <NUM> also forms an image of the subject pupil <NUM> onto the plane of optical stop <NUM>, which thus defines a small, virtual viewing window on the subject pupil <NUM> for the camera <NUM> to look through into the retina <NUM>. The illumination beams 32a-32n are thus respectively focused at the subject pupil <NUM> and the focal spots are pre-positioned outside the virtual viewing window. Therefore, any scattering light of illumination beams 32a-32n scattered outside this virtual viewing window will be substantially blocked from getting into the image recording device <NUM>.

In an illustrative example, the wide field fundus camera <NUM> may provide a static field of view of <NUM> degrees or wider on the subject retina <NUM>. In this illustrative example, the objective lens <NUM> has an optical power of about 120D and a diameter of about <NUM>. The objective lens <NUM> has thus a back focal length of shorter than <NUM> and a small working distance of approximate <NUM> millimeters with respect to the subject cornea <NUM>. The objective lens <NUM> may be an aspherical lens such that to have relative lightweight and to produce optimal image quality over the subject retina <NUM>.

A contact lens <NUM> may be positioned in front of the aspherical objective lens <NUM> and in direct contact with the subject cornea <NUM>. The contact lens <NUM> may or may not have optical power. <FIG> shows how a contact lens <NUM> is incorporated with the aspherical objective lens <NUM> to produce a first retinal image of the retina <NUM>. In an illustrative example, the contact lens has a diameter of about <NUM> to fit for the small eyeball <NUM> of infants.

There are commercially available aspherical lenses for retinal viewing, with indirect ophthalmoscopes or slit lamp microscopes. For instance, an aspherical lens integrated with a contact lens can be found in an Ocular ORMR-2x (Ocular Instruments, Bellevue, Washington, United States of America).

The image recording device <NUM> is located at a second end of the wide field fundus camera <NUM> and is to view and to photograph fundus image through objective lens <NUM>. Also, this image recording device <NUM> is in an illustrative example able to perform auto-focusing and auto-exposure control. The image recording device <NUM> in an illustrative example may include a consumer image recording device that includes advanced features of auto-focus, auto-exposure, real time display, and image storage and transfer, and that is compact, lightweight, and easy to use. The image recording device <NUM> may have built-in function to readily transfer its recorded image to a local computer or other processor for internet connectivity and telemedicine networks. The image recording device <NUM> as an illustrative example may have a resolution over <NUM> mega pixels and have an entrance pupil of <NUM> or bigger to receive all light passing through the optical stop <NUM>. The image recording device <NUM> may have a feature of a custom setting and be capable of saving working parameters for convenient operation. The image recording device <NUM> may have a separate display <NUM> for easy viewing, to provide a desirable viewing angle, display size, and display distance.

The image recording device <NUM> in an illustrative example is a smart lens type of consumer camera, such as a Sony QX100 (Sony Corporation, Japan). In this illustrative example, the image recording device <NUM> is coupled with the display <NUM> via Wi-Fi, and the display <NUM> may be a wireless device such as an iPhone or an iPad. Also this image recording device <NUM> may have high sensitivity and high resolution operation.

The plurality of illumination beam projectors 30a-30n may include two or more illumination beam projectors 30a-30n. Each of the projectors 30a-30n projects an illumination beam 32a-32n at an angle toward the objective lens <NUM>. In an illustrative example, each illumination beam 32a-32n has a small vergency and has a beam size to cover the illumination aperture <NUM>. This way, each illumination beam 32a-32n is to mimic the illumination of an indirect ophthalmoscope and to illuminate a portion of an image on the subject retina <NUM>. In an illustrative example, the plurality of illumination beam projectors 30a-30n produces four illumination beams 32a-32n, of which each illuminates a quadrant of the field of view on the subject retina <NUM>.

A wide field fundus camera <NUM> may be operated in the mydriatic condition, and white light illumination can be used for both aligning and photographing the subject retina <NUM>. In an illustrative example, each of the plurality of illumination beam projectors 30a-30n includes a high brightness, high power white LED and a projection lens to produce a white light illumination beam 32a-32n. The white light LED may include a warm white light source with a color temperature about <NUM> degrees of Kelvin. For radiation safety, each illumination beam 32a-32n is limited to project a few milli-watts of illumination power.

When another illumination condition is desirable, the illumination beam projectors 30a-30n can include one or more of high power, high brightness infrared LEDs. Further, the illumination beam projectors 30a-30n can include one or more of high power, high brightness LEDs capable of projecting a limited spectral range of illumination such as red, green, or blue light.

The projection angle of the illumination beams 32a-32n may be set so as to move corneal and crystalline lens reflections away from central viewing area. On the other hand, the projection angle of the illumination beams 32a-32n is limited to the minimum pupil size that the wide field fundus camera <NUM> is intended to use. For screening for ROP, the minimum pupil size is set to approximately <NUM>, and the projection angle of the illumination beams 32a-32n is thus set to about <NUM> to <NUM> degrees.

The narrow beam projector <NUM> is to project a narrow illumination beam <NUM> and to form a bright illumination feature on the retina <NUM> to facilitate auto focusing of the image recording device <NUM>. Typically, a consumer image recording device <NUM> requires a relatively high illumination level and a relatively high contrast target feature to obtain reliable and effective auto focusing. A bright and narrow slit beam illumination on or near the center of retina <NUM> is illustrated. In one illustrated example, the dimensions of the slit beam are about <NUM> long and <NUM> wide on the retina <NUM>.

The narrow illumination beam <NUM> is to project at an angle with respect to the viewing axis <NUM>. In an illustrative example, the narrow slit beam <NUM> is focused outside the virtual image window and has no overlap with the image beam path throughout the crystalline lens <NUM>.

The first polarizer <NUM> and the set of second polarizers 31a-31n may form a cross polarization condition to reject specular reflections of the illuminations beams 32a-32n back into the image recording device <NUM>. For a predetermined orientation of the first polarizer <NUM>, each of the second polarizers 31a-31n may be rotationally adjusted to form a precise condition of cross polarization. Specular reflections at surfaces of the objective lens <NUM> and contact lens <NUM> are particularly strong and necessary to remove. Specular reflections from first corneal surface (i.e. first Purkinje reflection), first surface of crystalline lens (i.e., third Purkinje reflection) and second surface of crystalline lens (i.e., fourth Purkinje reflection) can be a major source of image haze. A high extinction ratio of cross polarization is required for reflection haze reduction. The polarizers 31a-31n and <NUM> may be selectively thin film polarizers and have an extinction ratio of <NUM> or higher throughout the visible and infrared light spectrum.

The contact lens <NUM> may serve as an optical window of the wide field fundus camera <NUM> to interface with the subject cornea <NUM>. The contact lens <NUM> is illustrated to have an anti-reflection coating on its convex surface. As the illumination beams 32a-32n and the narrow illumination beam <NUM> are small and bright on the contact lens <NUM>, effort is required to minimize and to remove specular reflection from its convex surface that interfaces to air.

The focusing lens <NUM> in one illustrative example is an achromatic lens with a focal length about <NUM> to <NUM> and is positioned one focal length away from the back focal plane <NUM> of the objective lens <NUM>. In one illustrative example, the collimation lens <NUM> is to reimage the first retinal image formed by the objective lens <NUM> into distance, and thus the image recording device <NUM> is operated to focus at distance. This way, the focal length of camera <NUM> can be adjusted continuously to match a desirable field of view and the selected retinal image area can thus fill up the camera display <NUM>. As a result, the pixel resolution of the camera and its display can be optimized. Focusing lens <NUM> and objective lens <NUM> may form an optical afocal relay, to relay the outgoing beam from the subject pupil <NUM> to the image recording device <NUM>. The optical afocal relay has a scaling factor m, equal to the ratio of the focal lengths between the focusing lens <NUM> and the objective lens <NUM>. In an illustrative example, the focusing lens <NUM> has a focal length of <NUM>, and the optical afocal relay has a scaling factor m of about <NUM>.

Optical stop <NUM> may be positioned in front of the image recording device <NUM> and is conjugated with the working plane <NUM> of the wide field fundus camera <NUM> via objective lens <NUM>. The optical stop <NUM> has an aperture corresponding to a predetermined virtual viewing window on the subject pupil <NUM>. For instance, for a scaling factor of <NUM> and a virtual viewing window of <NUM> on the subject pupil <NUM>, the optical stop <NUM> is thus <NUM>. In operation, the subject pupil <NUM> is aligned with the working plane <NUM>, and the optical stop <NUM> blocks any light scattered from outside the virtual viewing window on the subject pupil <NUM>. The aperture of the optical stop <NUM> may also be limited to the effective aperture of the image recording device <NUM>.

The electronic controller <NUM> is to couple with the image recording device <NUM> and to power the illumination projectors 30a-30n and the narrow beam projector <NUM>. In an illustrative example, the electronic controller <NUM> powers the illumination projectors 30a-30n at a low power level during alignment and then ramps up them to a high power level for photographing the subject retina <NUM>. The power level of each of the illumination projectors 30a-30n can be controlled in a programmable manner. This way, the illumination projectors 30a-30n can be synchronized with the image recording device <NUM> to take multiple retinal images with various on-off configurations and time sequences.

The display <NUM> may couple with and display real-time images of the image recording device <NUM>. In an illustrative example, the display <NUM> is a high definition monitor and is coupled wirelessly with the image recording device <NUM>. For instance, the image recording device <NUM> may be a Sony QX100 (Sony Corporation, Japan) and the display may be an iPad (Apple, Cupertino, California, United States of America) and data transfer between the two devices may be through Wi-Fi built into the devices.

The images captured by the image recording device <NUM> may be stored in the camera <NUM>, monitored at the display <NUM>, and transferred to a local computer or other networked computers. The images captured by the image recording device <NUM> may thus be viewed through the network, and retinal diseases can be diagnosed by a retinal professional in a local or remote location.

A digital controller <NUM> may be used to independently control each illumination beam projector 30a-30n. In an illustrative example there are four independent LED beam projectors controlled by a digital controller. The controller may be connected to a tablet through its USB port and the user interface to the image recording device <NUM> and the digital controller <NUM> may be provided on the tablet display.

In <FIG>, an illustrative examples demonstrates how the user can control each of the four independent beam projectors 30a-30n and turn each one on or off via an illumination pattern selector <NUM>. The independent beam projectors 30a-30n may also be serially programmable and the pattern, timing, and beam illumination intensity can be controlled by the user via an illumination mode selector <NUM>. Power level for each independent beam projector 30a-30n may be controlled for both real-time live-view imaging of the retina, as well as flash photography via an illumination level adjustor <NUM>, wherein for flash photography the illumination beam projectors 30a-30n may be temporarily adjusted to higher intensity than in live-view imaging mode, for the purpose of final photo acquisition or auto-focusing purposes. Rapid sequential serial illumination control of each independent beam projector 30a-30n may allow the retinal view provided by each independent beam projector to be shown simultaneously in separate live-view images of the retina <NUM>, <NUM>, <NUM>, <NUM> For example one of four independent illumination beam projectors 30a-30n can be individually turned on and the retinal image resulting from each of four independent beams then shown in four separate panels on the same display <NUM>, <NUM>, <NUM>, <NUM>. In an illustrative example, each independent beam projector 30a-30n may be turned on for less than <NUM>, serially turning on each beam projector 30a-30n one at a time, allowing acquisition of the views provided by each of the four independent beam projectors in less than <NUM>. This timing can prevent lag in the live-view and allow the user to align the camera with the eye to optimize illumination provided by each independent beam projector 30a-30n.

In a separate illustrated example in <FIG>, a single live view image of the retina may be provided, and each independent beam projector 30a-30ncan be turned on and then off for a discrete period of time in a rotating clockwise or other programmed manner, one or more projector beams at a time, to allow the user to see the illumination provided by each beam projector for assessing alignment of the camera with the eye prior to final retinal image acquisition. For example, one of four independent beam projectors 30a-30n may be turned on for <NUM> <NUM>, then turned off, then the next independent beam projector is turned 1001on for <NUM>, then turned off, then the next independent beam projector is turned <NUM> is turned on for <NUM>, then turned off, then the next independent beam projector is turned <NUM> is turned on for <NUM>. This sequence of beam illumination control could be repeated until a final retinal image is acquired. The four panels shown in <FIG> <NUM>, <NUM>, <NUM>, <NUM> provide an example display seen at four different points in time, and would appear to the user as a rotating beam in real-time. Each independent beam projector 30a-30n may create a clear quadrant of viewing of the retina <NUM>, <NUM>, <NUM>, <NUM> as well as an area of lens haze and reflections <NUM>, <NUM>, <NUM>, <NUM> due to scattering of the illumination beam in objective lens <NUM>, and the human lens <NUM>.

A method may be used to process the multiple retinal images provided by each independent projector beam 30a-30n and to stitch them into a single fundus image. An illustrative example of this method is a processor circuit coupled to a memory circuit, the memory circuit including instructions that cause the processor circuit to receive imaging information corresponding to the plurality of retinal images and to provide a composite image including stitching together the plurality of retinal images into a single montage image. Please refer to <FIG>. In an illustrative example, a plurality of retinal images are acquired for four independent beam projector 30a-30n, turned on sequentially one at a time with the separate acquired retinal images shows as <NUM>, <NUM>, <NUM>, and <NUM>. Image haze from the specular reflections from the human lens is evident in each image and is indicated by <NUM>, <NUM>, <NUM>, and <NUM>. The portion of the each image without human lens haze <NUM>, <NUM>, <NUM>, <NUM> using said method can be stitched together to form a final montage image <NUM>. Blending may be performed of the separate images that form the final montage to eliminate seams and even exposure across the final montage. The method used to process said multiple retinal images may also identify the human lens haze (<NUM>, <NUM>, <NUM>, <NUM>), for illustrative example by both its contrast level and characteristic position based on which independent illumination projection beam is on and the angle the projection beam has with the eye. This haze may be masked by said image processing method before performing the final montage.

<FIG> shows an illustrative example of a wide field fundus camera <NUM> having an illumination beam projector 230n turned on for taking one of the multiple retinal images. The illumination beam projector 230n projects an illumination beam 232n onto the objective lens <NUM> at an angle with respect to the viewing axis <NUM>, mimicking the illumination configuration of an indirect ophthalmoscope. The illumination beam 232n is then focused on the working plane <NUM> and directed into subject pupil <NUM>. This illumination beam 232n passes through the subject pupil <NUM> and turns into illumination beam 233n to illuminate subject retina <NUM>.

Because the illumination beam 232n is projected at an angle and is shaped by the apertures <NUM> and <NUM>, the illumination beam 232n can thus be focused into subject pupil <NUM> and be away from the pupil center. In an illustrated condition, the illumination beam path is not overlapped with the image beam path inside the crystalline lens <NUM>, and scattering light scattered from the crystalline lens <NUM> is not captured by the image recording device <NUM>. In this way, image haze resulting from lens scattering of the illumination beam inside a less-transparent crystalline lens may be significantly reduced.

Also because the illumination beam 232n is projected at an angle and is shaped by the apertures <NUM> and <NUM>, the illumination beam 233n is not symmetric on the subject retina <NUM>. More than a quadrant of the field of view may be illuminated via such an illumination configuration. At this illumination condition, an image captured by the image recording device <NUM> may show only a portion but not the full field of view being illuminated. Therefore, multiple images may be required to capture the subject retina <NUM> in order to have a full field of view. In an illustrative example, four illumination beam projectors <NUM> are used and four retinal images may be captured in time sequence to provide a <NUM> degree field of view of the subject retina <NUM>.

<FIG> shows an illustrative example of a wide field fundus camera <NUM> having the narrow beam projector <NUM> turned on to facilitate autofocusing through less transparent crystalline lens <NUM> and reflection haze. The narrow beam projector <NUM> is to project a narrow illumination beam <NUM> and to form a bright illumination feature on the subject retina <NUM>. A consumer image recording device <NUM> may require a relatively high illumination level and a relatively high contrast target feature to obtain reliable and effective auto focusing. In particular, a bright and narrow slit beam illumination on or near the center of the subject retina <NUM> may be favorable for such autofocusing. In one illustrated example, the dimensions of the slit beam are about <NUM> long and <NUM> wide on the subject retina <NUM>.

The narrow slit beam <NUM> can be projected at an angle with respect to the viewing axis <NUM>. In an illustrative example, the narrow slit bean <NUM> is focused outside the virtual image window and has no overlap with the image beam path throughout the crystalline lens <NUM>. This way the slit beam image on the image recording device <NUM> is not blurred by scattering light from the crystalline lens <NUM>, and the narrow slit beam <NUM> thus serves to facilitate autofocusing through less transparent crystalline lens <NUM>.

<FIG> shows one illustrative example of a wide field fundus camera <NUM> having one slit beam projector 430n turned on to improve image taking through less transparent crystalline lens <NUM> and reflection haze. The slit beam projector 430n projects a slit beam 432n toward the objective lens <NUM>, in which the slit beam 432n has a narrow dimension in the incident plane of the illumination and a full dimension normal to the incident plane. As shown in <FIG>, such a slit beam 432n turns into a slit illumination beam 433n on the subject retina <NUM>. Also, such a slit beam 432n is confined away from the viewing axis <NUM> and thus may have a better clearance with the image beam path inside the crystalline lens <NUM>. Consequently, an overlapping region between the illumination beam path and the image beam path can be avoided inside the crystalline lens <NUM>, and thus image haze due to light scattering inside less transparent crystalline lens <NUM> may be substantially improved.

In an illustrative example, the slit beam 432n of <FIG> may provide a retinal slit image of approximate <NUM> degrees in the narrow dimension and <NUM> degrees in the length dimension, i.e., a dimension normal to the incident plane of the page. In one illustrative example if such a retinal slit image is taken at a rotational angle of <NUM> degrees separate from each other, then three of such retinal slit images may cover the full image of the subject retina <NUM>. In an illustrative example, three slit beam projectors 430a-430n are positioned <NUM> degrees from each other around the symmetric viewing axis <NUM>, and each projects a slit beam 432n with its narrow dimension orientated in its own incident plane. In this case, three retinal images may be taken to form a complete full field of view of the subject retina <NUM>. Similarly, in another illustrative example if the slit beam narrow dimension is about <NUM> degrees, five of slit beam projectors 430a-430n may be used and five slit beam images taken to cover a full field of view of the subject retina <NUM> with the objective lens <NUM>.

<FIG> shows an illustrative example of a hand piece <NUM> that integrates a central housing <NUM> for the multiple illumination projectors, a front housing <NUM> for the objective lens, an image recording device <NUM> and a contact lens <NUM> of the wide field fundus camera. In this illustrated example, the image recording device <NUM> is a Sony QX100 and it is affixed with the central housing <NUM> via a mechanical coupler <NUM>. The contact lens <NUM> may be mounted on a contact lens holder <NUM>, which is attached to the front housing <NUM>. This way the contact lens <NUM> may be removed with the holder <NUM> for easy sterilization.

In one illustrative example, the hand piece <NUM> may have an elongated shape, having dimensions about <NUM> in diameter and <NUM> long. In another illustrative example, for screening for ROP, the front end of the hand piece <NUM> is about <NUM> in diameter.

<FIG> shows an illustrative example of a hand piece <NUM> that integrates a central housing <NUM> for the multiple illumination projectors, a front housing <NUM> for the objective lens, an image recording device <NUM> and a contact lens <NUM> of the wide field fundus camera. In this illustrated example, the image recording device <NUM> is an Olympus Air A01 (Olympus Corporation, Japan) and it is affixed with the central housing <NUM> via a mechanical coupler <NUM>. In one illustrative example, images from the image recording device <NUM> may transmitted via Wi-Fi to a tablet display which in this illustrated example is a Samsung Galaxy Note <NUM>.

<FIG> shows the tablet display for one illustrated example of the electronic controller. In this example, four independent illumination beam projectors are controlled by the electronic controller. The electronic controller serially may turn on each illumination beam projector one at a time and the image recording device <NUM> may capture an image with each illumination beam. <NUM> shows the first illumination projector beam turned on with all other beams turned off, <NUM> shows the second illumination projector beam turned on with all other beams turned off, <NUM> shows the third illumination projector beam turned on with all other beams turned off, <NUM> shows the fourth illumination projector beam turned on with all other beams turned off. For example, the total time to turn on and off each of the four independent beams may be less than <NUM> milliseconds, with <NUM> milliseconds for each beam. This may allow a real-time display of how the retinal image formed by each independent beam will appear to assess alignment of each independent beam projector with the eye. The pattern of serial illumination control of each independent beam projector may be controlled by the user and may be programmable by selecting one of four possible patterns <NUM>. Each independent beam projector may be manually and independently turned on and off through a separate user control <NUM>. Power levels for each independent illumination projection beam may be controlled by the user both for real-time live examination and flash photography level when the final photo is captured by the image recording device <NUM>.

<FIG> shows one possible illustrated example for a method of image stitching of the plurality of images taken by independent illumination projector beams. In this example, four retinal images are taken, each having one of four independent beam projectors turned on. <NUM> shows the first illumination projector beam turned on with all other beams turned off, <NUM> shows the second illumination projector beam turned on with all other beams turned off, <NUM> shows the third illumination projector beam turned on with all other beams turned off, <NUM> shows the fourth illumination projector beam turned on with all other beams turned off. Each independent beam projector may create a specular white reflection and haze <NUM>, <NUM>, <NUM>, <NUM>, from the human lens of the eye <NUM> and the objective lens <NUM>, but also illuminates a quadrant of the retina without lens haze <NUM>, <NUM>, <NUM>, <NUM>. The image processing method may remove the area in each illumination projector beam image where there is lens haze from the human lens <NUM>, <NUM>, <NUM>, <NUM>, and join together the portion of each illumination projector beam image without lens haze <NUM>, <NUM>, <NUM>, <NUM>.

Blending may be performed on the stitched pieces to seamlessly blend differences in exposure level of each illumination projector beam image. The final montage <NUM> may eliminate the lens haze <NUM>, <NUM>, <NUM>, <NUM> from the montaged image. The image processing method may include a processor circuit coupled to a memory circuit, the memory circuit including instructions that cause the processor circuit to receive imaging information corresponding to the plurality of retinal images and to provide a composite image including stitching together the plurality of retinal images into a single montage image. It may further include a processor circuit coupled to a memory circuit, the memory circuit including instructions that cause the processor circuit to receive imaging information corresponding to the plurality of retinal images and remove artificial reflection spots and lens haze from each of said plurality of retinal images.

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description.

Claim 1:
A wide field fundus camera (<NUM>, <NUM>, <NUM>, <NUM>) for imaging a retina (<NUM>), comprising:
an objective lens (<NUM>) having a symmetric viewing axis (<NUM>) and disposed to form a retinal image of a field of view;
an image recording device (<NUM>) disposed to capture said retinal image of said field of view;
a plurality of illumination beam projectors (30a-30n) positioned around said viewing axis and each configured to project an illumination beam (32a-32n) at a predetermined angle toward said objective lens and each thereby illuminating a portion of an image on the retina;
a first polarizer (<NUM>) disposed in front of said image recording device, to define a polarization orientation;
a set of second polarizers (31a-31n), each second polarizer disposed in front of a corresponding one of said illumination beam projectors and each of said second polarizers oriented to form a cross polarization condition with respect to said first polarizer; and
an electronic controller (<NUM>) programmed to power said plurality of illumination beam projectors in a sequential programmable manner and coupling with the image recording device to capture a plurality of retinal images in accordance with the sequential programmable manner.