Systems and methods for measuring and classifying ocular misalignment

A device for measuring and classifying ocular misalignment of a patient's eyes includes an enclosure, two lenses at the front of the enclosure, one corresponding to each eye of a patient, a divider within the enclosure, positioned laterally between the lenses, a screen within the enclosure, an integrated microprocessor connected to the screen, and at least one input control connected to the integrated microprocessor, at least one input control operable by the patient; where the integrated microprocessor generates and transmits two images to the screen, each image corresponding to each lens; where the integrated microprocessor receives input from the patient via at least one input control to manipulate at least one image on the screen; and where the integrated microprocessor calculates and outputs a quantification of ocular misalignment based on that input.

FIELD OF THE INVENTION

This invention relates generally to the fields of ophthalmology, optometry, orthoptics, pediatrics and neurology, and more specifically to a new and useful system and method for detecting and measuring and the direction and amount of misalignment of the eyes, as well as categorizing the deviations detected into normal patterns or patterns associated with specific disorders of the oculomotor system.

BACKGROUND

The human visual system integrates visual signals from the retina as well as the vestibular apparatus in the inner ear to generate signals to the extraocular muscles that control movements to the eyes and eyelids in order to maintain binocular vision. Lesions in the brain, brainstem, the cranial nerves directing the extraocular muscles, or the extraocular muscles themselves can all result in misalignment of the eyes (strabismus). Example of such lesions include, but are not limited to stroke, intracranial vascular aneurysms, trauma, thyroid eye disease, demyelinating diseases, myasthenia gravis and congenital malformations. Misalignment of the eyes can also occur due to inadequate cortical stimulus for binocular fusion, such as uncorrected refractive error in one eye.

The cause of disorders of the oculomotor system can often be determined by the pattern of the resulting ocular deviation. One example is a left intranuclear ophthalmoplegia, in which the eye movements are completely normal except that the left eye cannot move to the right in right gaze. In some cases, identifying the correct pattern of ocular deviation can be critically important to rule out life-threatening emergencies such as carotid artery dissections or intracranial vascular aneurysms. The treatment of many disorders of ocular misalignment, often with surgery to strengthen, weaken or move the extraocular muscles, is also highly dependent on accurate measurement and characterization of the ocular misalignment. Critically, strabismus in children can lead to permanent loss of vision, including blindness, if untreated prior to critical developmental age (approximately 8 years).

Measurement of ocular misalignment must be done, at present, by highly-trained experts, such as pediatric ophthalmologists, neuro-ophthalmologists, or orthoptists. This measurement is referred to as the prism cover test (PCT), and is usually performed by placing prisms in front of the patient's eyes and analyzing the movement of the eyes as the patient is forced to alternate the eye used for fixation on a visual target. This is done in various positions of gaze, requiring the use of both near and distant fixation targets, and sometimes with the head tilted to one side or the other. The distant fixation target is approximately 6 m from the patient's eyes; as a result, the prism cover test requires a large space in which the test can be performed. The emerging pattern is interpreted by the expert examiner to make a diagnosis and guide treatment. The examiner also observes the eye movements, different directions of gaze, and grossly quantifies deficiencies to identify any restrictions in the extraocular muscles. Techniques involving specialized lenses also exist for measuring torsional misalignment (i.e., malrotation about the pupillary axis). Even when performed by experts, these techniques are inherently subjective and may be limited for pediatric patients and cognitively-impaired adults. Only one analog device exists that can perform objective measurement of all patterns of strabismus, the synoptophore, and it requires an expert operator.

Some forms of vertical strabismus can have deviations of different magnitudes depending on whether the head is vertical, tilted to the left or titled to the right. Measuring the deviation with different directions of head tilt is critical for identifying the affected neurologic pathway or muscles (the Parks-Bielschowsky three-step test). Additionally, torsional deviation may be minimized by tilting the head to one side or the other, and patients will naturally position their head accordingly to minimize diplopia. Therefore, the true torsional deviation can only be measured when taking into account head tilt. Additionally, some neurologic lesions may alter the patient's subjective sense of vertical and result in a head tilt in conjunction with a torsional deviation. However there are currently no devices that can simultaneously measure ocular deviation and head tilt.

Thus, there is a need for a device to objectively measure all patterns of strabismus while accounting for head position, without requiring an expert operator. This invention provides such a novel and useful method.

SUMMARY OF THE INVENTION

A device for measuring and classifying ocular misalignment may include an electronic display surrounded by a viewing enclosure with a central divider separating the images between the left and right eyes, referred to henceforth as “the viewer”.

A device for measuring and classifying ocular misalignment of a patient's eyes may include an enclosure, two lenses at the front of the enclosure, one corresponding to each eye of a patient, a divider within the enclosure, positioned laterally between the lenses, a screen within the enclosure, an integrated microprocessor connected to the screen, and at least one input control connected to the integrated microprocessor, at least one input control operable by the patient; where the integrated microprocessor generates and transmits two images to the screen, each image corresponding to each lens; where the integrated microprocessor receives input from the patient via at least one input control to manipulate at least one image on the screen; and where the integrated microprocessor calculates and outputs a quantification of ocular misalignment based on that input.

A method for measuring and classifying ocular misalignment may include providing a viewer, which includes an enclosure, two lenses at the front of the enclosure, one corresponding to each eye of the patient, a divider within the enclosure, the divider positioned laterally between the lenses, and a screen within the enclosure; displaying on the screen two different images, one corresponding to each lens, where each eye of the patient sees a different image; receiving input from the patient, where the input aligns the images based on the patient's perception; and determining the misalignment between the images that remains after the receiving input.

DETAILED DESCRIPTION

A device for measuring and classifying ocular misalignment generally may include a viewing enclosure with at least one lens for each eye to focus the image from a display, and a divider to separate the images presented to each eye. The device also may include a microprocessor to control the display, process inputs from various sensors and from the user via buttons on the outside of the enclosure.

Referring toFIGS.1a-1b, one embodiment of a viewer20is shown. The viewer20includes a viewing enclosure1, which may encase a screen2and lenses3a,3b. As is standard terminology in the art, the lenses3a,3bmay be referred to as oculars as well as lenses. A wheel and gear system4may be provided to allow the lateral position of the lenses3a,3bto be adjusted to match the interpupillary distance of the patient. According to other embodiments, the lateral position of the lenses3a,3bmay be adjusted in any other suitable manner. The lenses3a,3bare separated from the screen2by any distance that is long enough to allow for a useful diagnostic process, and short enough so that the viewing enclosure1does not become cumbersome. As one example, the lenses3a,3bmay be separated from the screen2by a distance that is substantially 3.8 cm. As another example, the lenses3a,3bmay be separated from the screen2by a distance that is between substantially 3.7-3.9 cm. As another example, the lenses3a,3bmay be separated from the screen2by a distance that is between substantially 3.5-4.0 cm. As another example, the lenses3a,3bmay be separated from the screen2by a distance that is between substantially 3.0-4.5 cm. As another example, the lenses3a,3bmay be separated from the screen by a distance of less than or equal to 10 cm, less than or equal to 15 cm, less than or equal to 20 cm, or less than or equal to 25 cm. One or more input controls are provided. As one example, the input controls are buttons5aand5b, located on an upper surface of the enclosure1, and provide input to the device, as described in greater detail below. The buttons5a,5balternately may be placed on a different location on the enclosure. According to other embodiments, the buttons5a,5bmay be placed on a separate handheld device that is connected to the viewer20via a cord, via a wireless connection, or in any other suitable manner. Referring also toFIG.8, as another example of an input control, an input control may be a joystick10used in conjunction with, or instead of, buttons5a,5bto provide input to the viewer20. A divider22may be located laterally between the lenses3a,3b. The divider22may be substantially planar and substantially vertical. Advantageously, the divider22may be matte black to minimize or prevent light emitted from the screen from reflecting from either lateral surface of the screen2. The divider22allows one screen to be used to display two separate images to the patient, one through each lens3a,3b. In this way, a separate and distinct image may be presented to each eye of the patient.

Referring also toFIG.1C, one embodiment of the viewer20includes an integrated microprocessor40that is used to display images on the screen2. An embodiment of the viewer may include at least one gyroscope42and/or at least one gravitometer44. Where the enclosure1is configured to be worn by the patient, the gyroscope42and/or gravitometer44detect head motion of the patient, generate data corresponding to such head motion, and transmit that head motion data to the integrated microprocessor40. The integrated microprocessor40also may receive other input from the patient, such as button presses from the buttons5a,5b. The integrated microprocessor40may output data to a secondary screen for use by the examiner, via at least one communications port46. Each communications port46may be configured for wired or wireless connection to a secondary screen, such as a monitor, tablet, laptop computer or desktop computer. A battery48or other power source is connected to the integrated microprocessor40to provide power thereto.

Referring also toFIG.6, the screen2, gyroscope42, gravitometer44, integrated microprocessor40and/or communications port46may be provided by a smartphone or tablet80. The smartphone or tablet80is inserted into the enclosure1into a receiver82in the enclosure1, with the screen2facing the lenses3a,3b. The use of a smartphone or tablet80may increase the convenience of use of the viewer20, and decrease the cost of the viewer20significantly, thereby enhancing access to screening for more patients.

In use, the enclosure1is placed in proximity to the patient's eyes, like a pair of goggles. The enclosure1may be connected to a strap or straps that allow the patient to wear the enclosure1during testing of his or her vision. By using the strap or straps, the enclosure1(and thus the viewer20as a whole) may be fixed substantially relative to the patient's head during the examination, facilitating the use of at least one gyroscope42and/or gravitometer44as part of the examination. According to other embodiments, the enclosure1may be held by the person administering the exam, may be mounted to a stand9such as a tripod (referring also toFIG.7), or may be positioned or mounted in any other suitable manner. The stand9optionally may telescope and/or retract, and/or may be detachable from the viewer20.

Referring also toFIG.2, two images50a,50bare displayed on the screen2, where those images50a,50bare used to quantify torsional misalignment of the patient's eyes. The images50a,50bare displayed on the screen2, separated by the divider22, such that the image50ais viewed by the patient through lens3a, and the image50bis viewed by the patient through lens3b. Each image50a,50bincludes a bar52a,52b, where the bars52a,52bare shown rotated to different angles relative to one another. For example,FIG.2shows the bars52a,52brotated 15 degrees relative to one another. Thus, as seen inFIG.2, when displayed on the screen2, the left eye of the patient sees bar52athrough the left lens3a, and the right eye of the patient sees bar52bthrough the right lens3b. Torsional misalignment is quantified by making the bars appear parallel when viewed by the subject using the viewer2. Using the buttons5a,5b, or other inputs, the subject's task is to rotate one of the images50a,50buntil the two bars52a,52bappear to be parallel with each other. The residual disparity in rotation at the end of this task—that is, the angle between the two bars52a,52bwhen the patient perceives the two bars52a,52bto be parallel—is the angle of torsional misalignment between the patient's two eyes. That angle of torsional misalignment is calculated by the integrated microprocessor40, and communicated by the integrated microprocessor to the examiner. If a head tilt is detected by the gyroscope42or gravitometer44during this test, it can be quantified and compared to the torsional ocular deviation, if present, to detect an ocular tilt reaction (aka skew deviation), indicative of a lesion somewhere along the pathway from the brainstem to the utricle of the inner ear.

Referring also toFIG.3, two images60a,60bare displayed on the screen2, where those images60a,60bare used to quantify vertical and horizontal misalignment of the patient's eyes. The images60a,60bare displayed on the screen2, separated by the divider22, such that the image60ais viewed by the patient through lens3a, and the image60bis viewed by the patient through lens3b. The images60a,60bare different from one another and are located at different horizontal and/or vertical positions relative to one another. As seen inFIG.3, the image60ais a bird and the image60bis a cage. According to other embodiments, the image60amay be a cross and the image60bmay be a circle. Alternately, the images60a,60bmay be any other suitable images. Thus, as seen inFIG.3, when displayed on the screen2, the left eye of the patient sees bird60athrough the left lens3a, and the right eye of the patient sees cage60bthrough the right lens3b. Vertical and horizontal misalignment is quantified by moving the bird60ainto the cage60bwhen viewed by the subject using the viewer2. Using the buttons5a,5b, or other inputs, the subject's task is to move the bird60ainto the cage60b; that is, to move the two images60a,60binto alignment with one another. The residual disparity in horizontal displacement between the images60a,60bat the end of this task—that is, the horizontal distance between the center of the bird60aand the center of the cage60bwhen the patient perceives the bird60ato be centered in the cage60b—is converted to an angle of horizontal deviation between the patient's two eyes. Similarly, the residual disparity in vertical displacement between the images60a,60bat the end of this task—that is, the vertical distance between the center of the bird60aand the center of the cage60bwhen the patient perceives the bird60ato be centered in the cage60b—is converted to an angle of vertical deviation between the patient's two eyes. The angles of horizontal and vertical deviation are calculated by the integrated microprocessor40, and communicated by the integrated microprocessor to the examiner.

The angles of horizontal and vertical deviation may be calculated by the integrated microprocessor40in any suitable manner. As one example, the image of the bird60amay be displaced Xppixels to the right from the location it would occupy if the patient exhibited no horizontal deviation. The resolution of the screen2in pixels/millimeter is known, so the distance of Xppixels can be converted to a distance of Xmmillimeters. The distance Z in millimeters from the eye to the screen2is also known, from the geometry of the viewing enclosure1. The horizontal angle of deviation θ is then computed using the trigonometric equation tan θ=Xm/Z. The sign of Xmmatters in the determination of the direction of rotation (in or out). The vertical deviation is calculated in an analogous manner.

When measuring vertical and horizontal displacement in the setting of a deviation, the subject will not be looking through the center of the lens3a,3b. The prismatic distortion that results will skew the measurements. For example, if the image of the cage60bis displaced to the right it will appear to the patient to be even farther right than it actually is, and that distortion is non-linear. This distortion may be rectified by performing a transformation of the screen coordinates using the Brown-Conrady model of lens distortion, or other similar approach (Brown, Duane C. (May 1966). “Decentering distortion of lenses” Photogrammetric Engineering. 32 (3): 444-462, Conrady, A. E. (1919). “Decentered Lens-Systems”. Monthly Notices of the Royal Astronomical Society. 79 (5): 384), which are hereby incorporated by reference in their entirety. Such a transformation is applied to the image coordinates before they are displayed to the patient on the screen2, so that the images (such as the bird60aand cage60b) appear to the patient to move in a linear manner on the screen2as the patient adjusts them, and the calculation in the preceding paragraph is effective and accurate.

If there is a vertical deviation, additional measurements can also be performed with the head tilted to the left and to the right, with the gyroscope42and gravitometer44used to measure the angle of head tilt. The device can compare the measurements using an automated Parks-Bielschowsky three-step test to identify the weak muscle leading to vertical strabismus. By placing the target shape in an off-center position, the deviation can be measured in different positions of gaze. Referring also toFIG.4, the combination of these measurements can be output to the secondary display in the form of a Hess chart70, allowing the examiner to analyze the pattern of strabismus and identify the afflicted neuromuscular pathways. The Hess chart analysis can also be analyzed algorithmically in an automated fashion. In the example ofFIG.4, the Hess chart70shows that limited up-and-to-the-right gaze of the right eye is demonstrated due to restriction or weakness of the right inferior oblique muscle (RIO).

The extra ocular movements can also be directly examined. Referring also toFIG.7, in another embodiment, the viewer20may be equipped with a camera8that can capture the eyes in each of the nine positions of gaze (forward, up, left, down, right, up-and-to-the-right, up-and-to-the-left, down-and-to-the-right, down-and-to-the-left. Each eye is then identified in each image captured by the camera8using any of the known computer vision algorithms for this purpose (e.g., neural nets). The corneal limbus can then be identified in the region of interest corresponding using the algorithm described in P{hacek over (a)}tr{hacek over (a)}ucean V., Gurdjos P., von Gioi R. G. (2012) A Parameterless Line Segment and Elliptical Arc Detector with Enhanced Ellipse Fitting. In: Fitzgibbon A., Lazebnik S., Perona P., Sato Y., Schmid C. (eds) Computer Vision—ECCV 2012. ECCV 2012. Lecture Notes in Computer Science, vol 7573. Springer, Berlin, Heidelberg for ellipse detection, or any other similar computer vision algorithm for the detection ellipse segments. The eccentricity of the ellipse corresponding to the corneal limbus is then used as a quantitative determination of the amount of eye rotation for the implicated eye in a given position of gaze and is output to the examiner, such as in the form of a Hess chart70ofFIG.4.

Referring also toFIG.5, another embodiment of the viewer20is shown, in which the screen2is split into two screens2a,2b, each viewable from a separate ocular6a,6b. The oculars6a,6bcan swivel relative to each other. The subject swivels the oculars6a,6buntil the images in the display appear aligned translationally. The horizontal and vertical angles of the oculars6a,6brelative to each other are quantified to determine the horizontal and vertical misalignment of the eyes. The physical angle of the two oculars6a,6brelative to one another may be determined in any suitable manner, and transmitted to the integrated microprocessor40. As one example, a standard Cartesian coordinate system is established, where the z axis points forward in the direction of the patient's nose, perpendicular to the frontal plane; the y axis (axial) is up and down (vertical), and the x axis is left and right (horizontal). To determine the angles between the oculars6a,6bin the xz and yz planes, two sensors may be used to determine those angles. As one example, those sensors may be potentiometers (not shown) physically coupled to those axes of rotation, so that the angles between the oculars6a,6bin the xz and yz planes can be directly measured from the electrical resistance at each of the potentiometers. As in the other embodiments, the images on the displays can be rotated relative to each other to quantify torsional misalignment. Infrared cameras7facing the eyes may be used to track the pupil movements, and can provide additional information about ocular misalignment.

FIG.8shows yet another variation in which a joystick or other controller10is used to provide input to the device by the subject. A PC11, or other type of remote display, is used to mirror the images seen by the subject and to provide output data to the examiner. The controller and PC may be tethered to the viewer using a wired serial or bus connection12, or a wireless connection13implementing Bluetooth or other wireless communication protocol.

As used in this document, both in the description and in the claims, and as customarily used in the art, the words “substantially,” “approximately,” and similar terms of approximation are used to account for manufacturing tolerances, manufacturing variations, manufacturing imprecisions, and measurement inaccuracy and imprecision that are inescapable parts of fabricating and operating any mechanism or structure in the physical world.

While the invention has been described in detail, it will be apparent to one skilled in the art that various changes and modifications can be made and equivalents employed, without departing from the present invention. It is to be understood that the invention is not limited to the details of construction, the arrangements of components, and/or the method set forth in the above description or illustrated in the drawings. Statements in the abstract of this document, and any summary statements in this document, are merely exemplary; they are not, and cannot be interpreted as, limiting the scope of the claims. Further, the figures are merely exemplary and not limiting. Topical headings and subheadings are for the convenience of the reader only. They should not and cannot be construed to have any substantive significance, meaning or interpretation, and should not and cannot be deemed to indicate that all of the information relating to any particular topic is to be found under or limited to any particular heading or subheading. The purpose of the Abstract of this document is to enable the U.S. Patent and Trademark Office, as well as readers who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The Abstract is not intended to define the invention, nor is it intended to limit to the scope of the invention. Therefore, the invention is not to be restricted or limited except in accordance with the following claims and their legal equivalents.