Patent Description:
With normal vision, an individual is able to focus at objects located at different distances. Ideally, an individual is able to focus on distant objects, referred to as distance-vision, and on near objects, referred to as near-vision. The optical system of the eye uses numerous muscles to change the focus between these distances. These muscles adjust various aspects of the eye when transitioning between distance-vision and near-vision. The muscle adjustments include making subtle changes to the shape of the crystalline lens to adjust the focus of the lens, rotating the eyeballs to rotate their optical axes, and changing the size of the pupils.

Presbyopia is a natural deterioration of near vision, caused by loss of flexibility in the eye's crystalline lenses as one ages. Presbyopia can be partially compensated by wearing "reading" glasses that correct near-vision refraction errors, so that the eye does not have to focus as strongly when gazing at near objects. Presbyopic persons need different optical corrections for near-vision and for distance-vision. However, using two eyeglasses and changing them frequently is distracting. To avoid continually exchanging eyeglasses, bifocals may be used that offer different optical corrections for near-vision and for distance-vision. The transition between these two vision regions can be abrupt or gradual. The latter eyeglasses are called Progressive Addition Lenses (PALs). Abrupt change bifocals have a visible line separating the two vision regions, while PALs have no lines or edges visible between the regions with different dioptric powers.

In spite of all this progress, some types of vision-related discomforts still persist. One of these discomforts is related to a shift of habits in the modern, digital lifestyle. A large and increasing fraction of professions require workers to spend a large and increasing fraction of their working time focusing at close-distance digital interfaces, including computer screens and mobile devices. The same is true for the private lives of many, spending hours playing video games, texting and checking updates on cell phones, among others. All these professional and behavioral shifts rapidly increased the time people spend looking at digital screens, devices, displays, and monitors at a much closer distance than before. The increased time of the eye being trained at near-vision images places excessive demands on the muscles involved in near-vision, often straining them beyond the comfort zone. This can lead to fatigue, discomfort, pain, or even digitally induced migraines. Up to now, there is no widely accepted consensus on the precise causation mechanism of these digital-device related visual discomforts, pains and migraines, even though millions of patients experience these pains every day. Therefore, there is a need for glasses, or other optometric solutions than can provide relief for digital eye discomforts.

<FIG> illustrate the basic problem of binocular misalignment. <FIG> illustrates that when we look at a near object, like the shown cross, our vision accommodates in two ways. First, we accommodate the optical power of our eyes <NUM>-<NUM> and <NUM>-<NUM> to image the near object at a distance L onto the retina of each eyes. This is often called the accommodative response A. Second, we rotate our eyes <NUM>-<NUM> and <NUM>-<NUM> inward by an angle α, so that the visual axes <NUM>-<NUM> and <NUM>-<NUM> of the eyes are pointing at the same near object. This response is often called the accommodative convergence AC. For obvious geometric reasons, the angle α of the accommodative convergence AC, relative to the straight forward reference axis, is directly related to the distance L of the accommodative response A: α=α(L). For healthy, well-aligned eyes the ratio of the accommodative convergence AC to the accommodative response A, AC/A, is a geometrically well-defined function, depending on the object distance L and the pupil distance PD of the two eyes.

<FIG> illustrate that eyes often display various forms of accommodative misalignments. In <FIG>, the two eyes each turn inward, but to a lesser degree that geometry would require. This leads to the accommodative convergence angle α being less than geometrically necessary by a misalignment angle β. In some detail, the visual axes of the eyes <NUM>-<NUM> and <NUM>-<NUM> should point into the direction denoted as the necessary accommodative alignment to properly see the near object, but, instead, they turn inward to a lesser degree and instead point to the direction denoted as relaxed or natural accommodative alignment.

<FIG> illustrates a case, when this lesser turn is asymmetrical. In the shown case, the visual axis <NUM>-<NUM> of the first eye <NUM>-<NUM> properly points to the direction of the necessary accommodative alignment, while the visual axis <NUM>-<NUM> of the second eye <NUM>-<NUM> is turned inward only to the direction of the relaxed or natural accommodative alignment, that is misaligned by the accommodative misalignment angle β.

<FIG>illustrate some types of accommodative misalignments. The definitions of misalignments used by different schools of optometry and by monographies show some discrepancies, and the techniques to characterize these misalignments are also varied. Therefore, the here-shown definitions are meant to be illustrative only, and analogues and equivalents are also within the scope of the illustrated terms.

To place the discussed misalignments into proper context, first the concept of fusing images is introduced. When our two eyes look at the same object, each eye creates its own visual perception. These perceptions are relayed from the eyes to the visual cortex, where the brain fuses the two images and creates a three dimensional (3D) perception of the viewed object. With optometric diagnostic systems, it is possible to test this image fusing. For example, two separate objects of the same shape can be separately projected into the two eyes with deflections, prisms, and mirrors that make the two projections appear to come from a single object. These visual perceptions will be fused by the brain into a perceived single image. Objects projected in this manner are called fusible objects, presenting fusible images.

If in an experiment the distance between the two objects is increased, or the deflection angles are increased, or the shapes of the objects are modified, then the projections into the two eyes start to differ. At some distance, or difference, between the objects, the discrepancy between the visual perceptions of the two eyes exceeds a threshold, and the brain stops fusing the two images into a single perception. Objects with such difference in distance, angle, or shape are called non-fusible objects, presenting non-fusible images.

With this preparation, <FIG> illustrate the concept of fixation disparity, as measured by a test device, often called the Mallet box. The Mallet box displays two vertically aligned bars, and an "X O X" horizontal "anchor". In some implementations, the two bars can be shifted sideways. In others, adjustable mirrors or prisms are placed in front of the patient's eye to achieve the same horizontal shift. With appropriate selective optics, the anchor and only one of the bars is shown for the first eye <NUM>-<NUM> as a centered bar <NUM>-<NUM>-c, and the same anchor plus only the other bar is shown for the second eye <NUM>-<NUM> as a centered bar <NUM>-<NUM>-c. The anchor and the centered bars <NUM>-<NUM>-c and <NUM>-<NUM>-c are clearly fusible. Accordingly, the brains of patients without accommodative misalignment problems will properly fuse these images.

<FIG> illustrates that patients with accommodative misalignments will not fuse the images properly. What is typically observed is that, while the images of the anchor, seen by both eyes, are properly fused into a single image, the bars are perceived as shifted. The first eye <NUM>-<NUM> perceives a shifted bar <NUM>-<NUM>-s, while the second eye <NUM>-<NUM> perceives a shifted bar <NUM>-<NUM>-s. The angle /between the line to the image center and one of the visual axes <NUM>-<NUM> and <NUM>-<NUM> is called fixation disparity.

<FIG> illustrate ways to measure the angle needed to counteract, or compensate the fixation disparity. In the system of <FIG>, the two bars are counter-shifted. A counter-shifted bar <NUM>-<NUM>-x is shown for the first eye <NUM>-<NUM>, and a counter-shifted bar <NUM>-<NUM>-x is shown for the second eye <NUM>-<NUM>. The bars are counter-shifted until the patient perceives the two bars as aligned. The angle corresponding to these counter-shifts, γ*, between the visual axes and line to the counter-shifted bars is measured and is typically referred to as an associated phoria. In the system of <FIG>, the bars are not counter-shifted. Instead, adjustable, or exchangeable prisms <NUM> are inserted in front of the patient's eyes. These prisms are adjusted or exchanged until the two bars are perceived as aligned by the patient. Then the prism angles, or the refraction angles of the refracted visual axes, are reported as the associated phoria γ*.

<FIG> illustrates how increasing a partial associated phoria partially compensates fixation disparity. Strictly speaking, the (full) associated phoria, that fully compensates fixation disparity, is given by the intersect of this curve with the partial associated phoria axis. If human vision were a purely optical process, the partial associated phoria would be simply equal to the negative of the partially compensated fixation disparity. Accordingly, the curve would be a straight line through the origin, tilted by -<NUM> degrees, pointing from the upper left corner to the lower right corner. However, <FIG> illustrates that human vision is much more complex, and perception and image processing play crucial roles in it. <FIG> shows four types of relations between the partially compensated fixation disparity and the partial associated phoria. Visibly, none of these lines are straight, none of them go through the origin, and two of them don't even intercept the horizontal axis. These type II and III relations mean that no amount of partial associated phoria can compensate the fixation disparity in full. Therefore, it remains a substantial challenge to determine the associated phoria that fully compensates a patient's fixation disparity. A convention is mentioned in closing: the fixation disparity is referred to as "exo", if the eyes do not turn inward to the necessary degree, while it is referred to as "eso" in those rare cases, when the eyes turn inward too much.

<FIG> illustrate a related visual misalignment called disassociated phoria. To characterize disassociated phoria, an experiment similar to that in <FIG> can be carried out, with the difference that instead of showing fusible images <NUM>-<NUM> and <NUM>-<NUM>, the optometrists show non-fusible images <NUM>-<NUM>-s and <NUM>-<NUM>-s for the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>. In <FIG>, these non-fusible images are the cross and the bar. As <FIG> illustrates, once the eyes are unable to fuse the images, often one or both of the visual axes rotate outward. In the shown asymmetric case, the visual axis <NUM>-<NUM> of the second eye <NUM>-<NUM> rotates outward by an accommodative misalignment angle δ. This angle δ of the outward rotation is measured and called disassociated phoria. In various applications, as below, the disassociated phoria is distributed over the two eyes evenly, thus the disassociated phoria per eye equaling δ/<NUM>. In some cases, e.g. as illustrated in <FIG>, the disassociated phoria δ may manifest itself unevenly and has to be distributed between the eyes accordingly.

<FIG> shows a particularly clear case, when simply no image is shown for the second eye <NUM>-<NUM>, the view of the second eye <NUM>-<NUM> is blocked. This is an extreme case of non-fusible images. As for <FIG>, in response to the block, the visual axis <NUM>-<NUM> of the second eye <NUM>-<NUM> rotates outward by a measurable disassociated phoria angle δ.

As a quantitative characterization of accommodation misalignments, including fixation disparity and disassociated phoria, several practitioners use the misalignment-impacted AC/A ratio. The AC/A is a ratio of the accommodative convergence angle reduced by the fixation disparity, α-δ/<NUM>, (expressed with its tangent, in terms of "prism diopters" Δ), divided by the accommodative distance L, expressed in diopters D. A typical definition of AC is AC=<NUM> tan(α-δ/<NUM>), in terms of prism diopters. For an average visual performance, an AC/A ratio of <NUM>-<NUM>Δ/D is necessary, while, remarkably, in large population segments the average of the misalignment-impacted AC/A ratio was measured to be about <NUM>Δ/D. Clearly, various forms of accommodative misalignment affect a large percentage of the population, and any progress towards relief from this is highly valuable.

A startling fact of the corresponding field of optometry is that the associated phoria angles and the disassociated phoria angles, determined by experienced practitioners, show remarkably wide variations. Experiments carried out on the same patient by different optometrists, and sometimes even by the same optometrist at different times, report phoria angles, expressed in prism diopters Δ, with a distribution having a standard deviation as much as 3Δ. (A prism diopter of 1Δ corresponds to a <NUM> prism refraction at <NUM> meter distance). The large variability of these methods precludes the effective determination and compensation of accommodative misalignments.

This exceptionally large standard deviation is probably due to several factors. These include the followings. (<NUM>) The methods of determination use the patient's subjective responses as key inputs. (<NUM>) Some methods use central images, while others use peripheral images for determining the associated phoria. The relative accuracy and relevance of these methods was not yet critically evaluated. (<NUM>) Most practitioners use a single measurement, or a single method, thus not benefiting from possibly important medical information that can be gleaned from carrying out multiple tests. (<NUM>) In a previous exploratory project, Applicants also discovered that the prismatic reaction of the eyes is quite different for moving test images. However, understanding the relation of optimal prismatic corrections based on static and moving test images is in its early stages. (<NUM>) While there are several ways to define prismatic misalignments, and they produce different prismatic predictions and diagnoses, eventually a single prism needs to be formed in the spectacles. It is far from obvious how to convert and combine the various diagnostically determined prismatic corrections into a single prism prescription. Applicants are not aware of a critical study that would have evaluated how the efficacy and variability of prism prescriptions depended on the possible combinations of the determined prismatic corrections.

For all of the above reasons, determining the prismatic power that optimally compensates accommodative misalignments remains a pressing medical need. <NPL>et al. , discusses the relationship between phoria and the ratio of convergence peak velocity to divergence peak velocity.

To address the above described medical needs, the invention provides an objective method to determine a binocular alignment, the method comprising: measuring, via an eye tracker, a disassociated phoria of a first eye and a second eye of a patient at an apparent distance; and determining an accommodative convergence of the first eye and the second eye at the apparent distance using the measured disassociated phoria; the determining comprising: presenting a first image for the first eye and a second image for the second eye, with the apparent distance vergence corrected with the measured disassociated phoria, using a stereo display; wherein the first image and the second image are fusible; projecting a first added central image for the first eye, and projecting a second added central image for the second eye, in an alternating manner, using the stereo display; and tracking an adjustment of the first eye in response to the projecting of the first added central image, and tracking an adjustment of the second eye in response to the projecting of the second added central image, using the eye tracker.

The systems described in the present patent document address the above articulated medical needs at least in the following aspects. (<NUM>) The described system and method determine the prismatic corrections only by objective measurements, without subjective input from the patient. This aspect alone greatly reduces the patient-to-patient and practitioner-to-practitioner variations of the results. In fact, studies on large samples of patients using Applicant's system and method determined prismatic corrections with a standard deviation reduced from the above mentioned 3Δ to well below 1Δ. This significant reduction of the results' standard deviation alone established the here-described method to the status of quantitatively predictive diagnostic methods. (<NUM>) The system and method use both central and peripheral test images, because of a newly developed understanding of how the peripheral and the central prismatic corrections are connected. Therefore, the described system and method is a promising platform to determine an optimal compromise prismatic prescription that strikes the best compromise for compensating both central and peripheral accommodative misalignments. (<NUM>) The described method has two stages, thus it determines the eventual prismatic correction in a second stage by building on the important misalignment information acquired in the first stage. As such, the method integrates knowledge determined by different methods and benefits from the information determined by all of them. (<NUM>) One of the stages of the method involves moving test images. Therefore, the eventually determined prismatic corrections capture and integrate the dynamic prismatic response of the eye as well. (<NUM>) The reliable repeatability and small variability of the above mentioned large scale study provided a compelling argument that Applicants' method combined the outputs of different methods in an objective and effective manner to produce a single optimized and objective prismatic correction. The here-described five aspects provide advantages individually and in combinations.

<FIG> illustrate a system <NUM> for determining a binocular alignment, and <FIG> illustrate a corresponding method <NUM> for determining the binocular alignment.

<FIG> illustrates that in some aspects, the system <NUM> for determining a binocular alignment can comprise a stereo display <NUM>, to project visible images for a first eye <NUM>-<NUM> and a second eye <NUM>-<NUM>; an accommodation optics <NUM>, to modify the projected visible images according to an apparent distance; an eye tracker <NUM>, to track an orientation of the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>; and a computer <NUM>, coupled to the stereo display <NUM>, the accommodation optics <NUM> and the eye tracker <NUM>, to manage a determination of the binocular alignment. In what follows, the eyes will be labeled as first eye <NUM>-<NUM> and second eye <NUM>-<NUM>. This labeling can correspond to a left eye and a right eye, or vice versa.

<FIG> shows a detailed illustration of some aspects of the system <NUM>. In some aspects, the eye tracker <NUM> can include infrared light emitting diodes, or IR LEDs, <NUM>-<NUM> and <NUM>-<NUM>, positioned close to a front of the system <NUM>, to project infrared eye-tracking beams on the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>, as well as infrared light sources <NUM>-<NUM> and <NUM>-<NUM>, to illuminate the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM> with an infrared imaging light. The infrared eye-tracking beams and the infrared imaging light get both reflected from the eyes <NUM>-<NUM> and <NUM>-<NUM>. The eye tracker <NUM> can further include infrared (IR) telescopes <NUM>-<NUM> and <NUM>-<NUM>, with infrared (IR) cameras <NUM>-<NUM> and <NUM>-<NUM>, to detect the infrared eye-tracking beams and the infrared imaging light, reflected from the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>.

Many of the elements of the system <NUM> are included in pairs, e.g., the infrared telescopes <NUM>-<NUM> and <NUM>-<NUM>. For simplicity of presentation, such pair of elements will be referred to only by their lead identifiers where doing so does not lead to misunderstanding, such as "the infrared telescope <NUM>", abbreviating "the infrared telescopes <NUM>-<NUM> and <NUM>-<NUM>.

<FIG> illustrates a resulting IR image <NUM>, as detected, or sensed, by the IR camera <NUM>. In this aspect, there are four IR LEDs <NUM>-<NUM>,. <NUM>-<NUM> for each eye separately. To avoid clutter, the "-<NUM>" or "-<NUM>" indicating a particular eye, is omitted in the description of <FIG>. The "-<NUM>". "-<NUM>" notation here refers to the four IR LEDs, all projecting IR eye tracking beams onto the same eye. The four IR LEDs <NUM>-<NUM>,. <NUM>-<NUM> project four IR eye-tracking beams onto the eye, which reflect from the cornea, creating four so called Purkinje spots P1-<NUM>,. P1-<NUM> in the IR image <NUM>. The "P1" notation refers to the reflection from the proximal surface of the cornea. The higher indexed Purkinje spots P2,. refer to reflections from deeper lying surfaces inside the eye, such as reflections from the proximal and distal surfaces of the capsule. The here-described aspects utilize the P1 Purkinje spots, while other aspects may employ higher indexed Purkinje spots.

The reflected IR imaging light of the IR light source <NUM> is detected by the IR camera <NUM> as well. The four Purkinje spots P1-<NUM>,. P1-<NUM> overlaid on the detected reflected IR imaging light together form the IR image <NUM>, as shown.

In some aspects, the eye tracker <NUM> can include an image recognition system <NUM>, to determine an orientation of the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>, using the detected infrared eye tracking beams, forming the Purkinje spots P1-<NUM>,. P1-<NUM>, and the detected infrared imaging light, together forming the IR image <NUM>. The image recognition system <NUM> can extract, for example, an image of the contour of a pupil <NUM>, using edge-recognition methods. Then it can determine an orientation of the eye <NUM> from the center of the pupil <NUM>. Separately, it can determine the orientation of the eye from the Purkinje spots P1-<NUM>,. Finally, it can employ a weighing algorithm to determine a "best result" orientation by combining the two determined orientations, using various well known image recognition and analysis techniques. The image recognition system <NUM> can be a separate processor, a separate application specific integrated circuit, or it can be implemented as a software deployed in the system-managing computer <NUM>.

<FIG> illustrate that the system <NUM> can further include infrared-transmissive visible mirrors <NUM>-<NUM> and <NUM>-<NUM>, one for each eye, to redirect the projected visible images <NUM>-<NUM> and <NUM>-<NUM>, from the stereo display <NUM> to the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>; and to transmit the reflected infrared eye tracking beam and the infrared imaging light, together <NUM>-<NUM> and <NUM>-<NUM>, from the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>. In these aspects, stereo display screens <NUM>-<NUM> and <NUM>-<NUM> of the stereo display <NUM> can be positioned peripheral to a main optical pathway of the system <NUM>, and the infrared telescopes <NUM>-<NUM> and <NUM>-<NUM> of the eye tracker <NUM> can be positioned in the main optical pathway of the system <NUM>. For reference, the accommodation optics lenses <NUM> -- mirror <NUM> -- IR telescope <NUM> axis for each eye is typically referred to as the main optical pathway in this embodiment. Also, for clarity's sake, in figures where the optical paths and beam are shown, some labels have been simplified.

<FIG> shows that in this aspect, the peripheral stereo display screens <NUM>-<NUM> and <NUM>-<NUM> can project visible images <NUM>-<NUM> and <NUM>-<NUM> towards the main optical pathway of the system <NUM>, that are redirected by the infrared-transmissive visible mirrors <NUM>-<NUM> and <NUM>-<NUM> toward the eyes <NUM>-<NUM> and <NUM>-<NUM>. At the same time, the reflected IR eye tracking beams and the reflected IR imaging lights, together <NUM>-<NUM> and <NUM>-<NUM>, reflected from the eyes <NUM>-<NUM> and <NUM>-<NUM>, are transmitted by the same infrared-transmissive visible mirrors <NUM>-<NUM> and <NUM>-<NUM> toward the IR telescopes <NUM>-<NUM> and <NUM>-<NUM> along the main optical pathway of the system <NUM>.

<FIG> illustrates another aspect, where the location of the stereo display screens <NUM> and the IR telescopes <NUM> is exchanged. <FIG> illustrates that this aspect can include visible-transmissive infrared (IR) mirrors <NUM>'-<NUM> and <NUM>'-<NUM>, to redirect the reflected infrared eye tracking beam and the reflected infrared imaging light, together <NUM>-<NUM> and <NUM>-<NUM>, reflected from the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>, toward the IR telescopes <NUM>-<NUM> and <NUM>-<NUM>. At the same time, the visible-transmissive infrared mirrors <NUM>'-<NUM> and <NUM>'-<NUM> can transmit the projected visible images <NUM>-<NUM> and <NUM>-<NUM>, from the stereo display screens <NUM>-<NUM> and <NUM>-<NUM> of the stereo display <NUM> to the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>. In these aspects of the system <NUM>, the stereo display <NUM> can be positioned in the main optical pathway of the system <NUM>, and the infrared telescopes <NUM> of the eye tracker <NUM> can be positioned peripheral to the main optical pathway of the system <NUM>. For reference, in this aspect, the accommodation optics lenses <NUM> -- mirror <NUM> - stereo display screen <NUM> axis for each eye is typically referred to as the main optical pathway in this aspect.

<FIG> illustrates a variant of the system <NUM> of <FIG>, in which the stereo display <NUM> can include a single stereo display screen <NUM>, and synchronizing glasses <NUM>. The synchronizing glasses <NUM> can be shutter glasses or polarized glasses. In this aspect, the projected visible images <NUM>-<NUM> and <NUM>-<NUM> of the left and right stereo display screen <NUM>-<NUM> and <NUM>-<NUM> of <FIG> are both displayed by the single stereo display screen <NUM> in a rapidly alternating sequence. The synchronizing glasses <NUM> can be precisely coordinated with this alternating sequence, allowing the projection of the visible images <NUM>-<NUM> and <NUM>-<NUM> to the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM> in a rapidly alternating manner, creating the impression of separate images being projected into these eyes. The synchronizing glasses <NUM> can be analogous to the 3D glasses used in the projection of 3D movies, and can rely on liquid crystal LCD layers that can rapidly change the circular polarization of the two lenses of the synchronizing glasses <NUM>. Such systems <NUM> can achieve smaller footprints for the system <NUM> that can be advantageous. For optimal operations, a sufficiently wide field of view for the stereo display screen <NUM> can be helpful.

Some aspects of the system <NUM> do not need to include the mirrors <NUM> or <NUM>'. In these systems, the eye tracker <NUM> may include small implementations of the IR cameras <NUM>, positioned close to the front of the system <NUM>, slanted at a sufficiently large angle so that the IR cameras <NUM> do not block the projections by the stereo display screens <NUM>. The image recognition system <NUM> of such implementations of the eye tracker <NUM> can include a geometric transformation unit to determine the direction of the eye visual axes from a substantially slanted IR image <NUM> and Purkinje spots P1,. P4, possibly some spots even being obscured by the slant.

In aspects of the system <NUM>, the accommodation optics <NUM> can include phoropter wheels <NUM>-<NUM> and <NUM>-<NUM> with a series of accommodation optics lenses <NUM>-<NUM> and <NUM>-<NUM> of varying optical power. These accommodation optics lenses <NUM> are useful to simulate the apparent distance for the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>.

As described below in relation to the method <NUM>, the system <NUM> can be employed to project visible images <NUM> at different apparent distances for a patient. Doing so can involve at least two technical solutions. First, inserting the accommodation optics lenses <NUM> with their variable optical power into the main optical pathway can create the impression of the projected visible images <NUM> being farther or closer. Second, projecting the visible images <NUM>-<NUM> and <NUM>-<NUM> closer or farther from each other can simulate an appropriate vergence of these images, another important factor in making these images appear as being at the apparent distance for the patient.

In some aspects, for the first technical solution, the accommodation optics <NUM> can include, in place of the phoropter wheel <NUM>, or in combination with the phoropter wheel <NUM>, curved mirrors, trial lenses, flip in/flip out lenses, adjustable liquid lenses, deformable mirrors, z-directionally movable mirrors, rotating diffractive optical elements, translating diffractive optical elements, variable focus moire lenses, or focusing lens groups.

<FIG> illustrate that for the second technical solution, the accommodation optics <NUM> can include a pair of rotatable deflectors <NUM>, rotatable prisms <NUM>, or adjustable prisms <NUM> (only one shown), to deflect the projection of the images <NUM>-<NUM> and <NUM>-<NUM> to the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>, to simulate a vergence of the apparent distance for the first eye and the second eye.

In some aspects, the vergence can be simulated not by the above optical elements, but by shifting the projecting of the projected visible images <NUM>-<NUM> and <NUM>-<NUM> with the stereo display screens <NUM>-<NUM> and <NUM>-<NUM> towards each other, in other words, projecting them closer to each other.

In some systems <NUM> the accommodation optics <NUM> and the stereo display <NUM> can be combined into a single light field display that includes a microlens array, where the projected visible images <NUM>-<NUM> and <NUM>-<NUM> shown on the stereo display screens <NUM>-<NUM> and <NUM>-<NUM>, combined with the optical characteristics of the microlens array can be used to vary the apparent distance of the projected visible images <NUM>-<NUM> and <NUM>-<NUM> as seen by a patient.

In some systems <NUM>, the accommodation optics <NUM> and the stereo display <NUM> can be combined into a single light field display that includes a mems scanner, a focus modulator, or a light source.

Having described the problem of prismatic or accommodative misalignments and embodiments of the system <NUM> that were developed to provide progress in the context of the misalignment problems, next, various methods <NUM> will be described for determining binocular misalignments using embodiments of the system <NUM>.

<FIG> illustrate a method <NUM> of how to use the above described aspects of the system <NUM> to determine a binocular alignment of the eyes <NUM>-<NUM> and <NUM>-<NUM>.

<FIG> illustrates that the method <NUM> includes a measuring <NUM> of a disassociated phoria of the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM> of a patient at an apparent distance, and a determining <NUM> of an accommodative convergence of the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM> at the apparent distance using the measured disassociated phoria. As mentioned earlier, the method <NUM> is a two-stage method, and thus its results integrate the information and knowledge revealed by the two different stages.

As described below in detail, in some embodiments, the measuring <NUM> can include projecting non-fusible visible images <NUM>-<NUM> and <NUM>-<NUM> for the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM> using the stereo display <NUM> of the system <NUM>. For the purpose of describing the method <NUM> more concisely, the visible images <NUM>-<NUM> and <NUM>-<NUM> of <FIG> will be simply referred to as images <NUM>-<NUM> and <NUM>-<NUM> in what follows.

Examples of projecting non-fusible images in order to determine a disassociated phoria have been described, e.g., in relation to <FIG>. There, the two non-fusible images <NUM>-<NUM>-s and <NUM>-<NUM>-s were of comparable appearance, or dominance. Some embodiments of the method <NUM> also involve projecting such non-fusible images of comparable dominance.

In other embodiments, the projecting can include projecting a dominant image for the first eye <NUM>-<NUM>, and projecting a non-dominant image for the second eye <NUM>-<NUM>. As described in relation to <FIG>, the eye <NUM>-<NUM> that sees the non-dominant image often starts wandering off after the brain's efforts to fuse the two non-fusible images fail. The measuring <NUM> includes tracking the eyes <NUM>-<NUM> and <NUM>-<NUM> with the eye tracker <NUM>, and determining when the wandering eye <NUM>-<NUM> eventually achieves a relaxed orientation. Achieving this relaxed state can be inferred, for example, by the eye tracker <NUM> determining that the movement of the eye <NUM>-<NUM> slowed below a threshold, or changed from a directional movement to a random jitter, or came to a halt. Once the eye tracker <NUM> determined that the eye <NUM>-<NUM> reached the relaxed state, the disassociated phoria can be measured by measuring an orientation of at least one of the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM> by the eye tracker <NUM>.

<FIG> describes implementations of these steps in more detail, and <FIG> illustrate these steps in a particular embodiment. In these embodiments, the measuring <NUM> can include the followings.

<FIG>, left panel illustrates that the projecting of a centered image step <NUM> can include projecting a centered image <NUM>-<NUM>, a cross in this case, on the stereo display screen <NUM>-<NUM> of the stereo display <NUM> of the system <NUM>. The projecting <NUM> can be done with an apparent distance vergence <NUM>. A reference axis <NUM>-<NUM> is introduced for reference as a central normal that connects a center of the first eye <NUM>-<NUM> with a center of the stereo display screen <NUM>-<NUM>. With this, the apparent distance vergence <NUM> can be characterized by an apparent distance vergence angle α=α(L), the angle that a first eye visual axis <NUM>-<NUM> makes with the reference axis <NUM>-<NUM> when looking at an object that is placed halfway between the two eyes <NUM>-<NUM> and <NUM>-<NUM> at the apparent distance L. More generally, the apparent distance vergence <NUM> will be represented by and referred to as the line directed from a center of the first eye <NUM>-<NUM> with the angle α(L) relative to the reference axis <NUM>-<NUM>, even if the first eye visual axis <NUM>-<NUM> is not pointing along this line.

The centered image <NUM>-<NUM> is centered in the sense that it is moved off the center of the stereo display screen <NUM>-<NUM> only by the apparent distance vergence angle α(L) to simulate the apparent distance vergence <NUM>. For brevity's sake, sometimes this angle will be only referred to as the vergence angle α. The definition of the first eye visual axis <NUM>-<NUM> can incorporate a lens or any other relevant portion of the accommodation optics <NUM>-<NUM>, through which the first eye <NUM>-<NUM> is observing the centered image <NUM>-<NUM>.

<FIG>, right panel illustrates the projecting of a distributed image step <NUM> for the second eye <NUM>-<NUM>, in this case, a set of irregularly placed balls or spheres of random size and position, without an apparent center. The centered image <NUM>-<NUM> is an example of a dominant image, and the distributed image <NUM>-<NUM> is an example of a non-dominant image. The centered, dominant image <NUM>-<NUM> and the distributed, non-dominant image <NUM>-<NUM> are examples of non-fusible images. Alternatively, the stereo display screen <NUM>-<NUM> can be simply darkened as another embodiment of the non-fusible distributed image <NUM>-<NUM>, instead of the irregularly placed balls, in analogy to the block in <FIG>.

<FIG> illustrates that, as described earlier, the second eye <NUM>-<NUM> will initially also turn inward by approximately the same apparent distance vergence angle α as the first eye <NUM>-<NUM>, but, after the brain fails to fuse the non-fusible central image <NUM>-<NUM> and distributed image <NUM>-<NUM>, the second eye <NUM>-<NUM> wanders away. The eye tracker <NUM> can execute the tracking step <NUM> of the second eye <NUM>-<NUM> until the optometrist, or an automated program, determines that the wandering second eye <NUM>-<NUM> reached a relaxed state from a stabilization of the tracked rotation in the identifying step <NUM>. This stabilization can be defined in various ways: from the eye coming to a stop, or an amplitude of the eye's jitter becoming less than a threshold, or a directional rotation of the eye evolving into a directionless wandering.

In the measuring step <NUM>, once the relaxed state has been identified in step <NUM>, the eye tracker <NUM> can measure the orientation of the relaxed second eye <NUM>-<NUM> by determining the angle δ the second eye visual axis <NUM>-<NUM> with the apparent vergence <NUM>. In this measuring step <NUM>, δ, the angular deviation of the relaxed second eye <NUM>-<NUM> from the apparent distance vergence <NUM> will be referred to as the disassociated phoria <NUM>, with its disassociated phoria angle δ. This definition is in close analogy with that of <FIG>. As mentioned before, small differences exist among various practitioner's definitions of the disassociated phoria.

In some related embodiments, the tracking step <NUM> may involve tracking a rotation of the first eye <NUM>-<NUM>, the second eye <NUM>-<NUM>, or both. In these embodiments, the disassociated phoria <NUM> can be defined from measuring <NUM> a first eye phoria angle <NUM>--<NUM>, a second eye phoria angle <NUM>--<NUM>, and determining the disassociated phoria δ as some type of a mean of δ-<NUM> and δ-<NUM>.

<FIG> illustrated that the steps <NUM>-<NUM> of the overall measuring step <NUM> can be performed as a near vision distance, e.g. L being in the range of <NUM>-<NUM>.

<FIG> illustrate that the same steps <NUM>-<NUM> can be also performed as part of a distance vision test, when the apparent distance is L large, and the apparent distance vergence angle is α=<NUM>. In related embodiments, L can be in the <NUM>-<NUM> range. Expressed in diopters, the method <NUM> can be performed at near vision distances corresponding to <NUM>-3D, at distance vision distances corresponding to <NUM>-<NUM>.

To summarize, the result of the measuring step <NUM>, the first stage of the method <NUM>, is the disassociated phoria <NUM>, with its disassociated phoria angle δ. The second stage of the method <NUM>, the determining step <NUM>, carries out additional tests of the prismatic misalignment that build on the just determined disassociated phoria <NUM>. Therefore, the overall method <NUM> is a combination of the first and second stages and thus the method <NUM> integrates two distinct tests of prismatic misalignments, and thus integrates knowledge and data about two different types of the binocular alignment. Doing so promises a qualitatively more complete treatment and a qualitatively better improvement of the visual acuity.

<FIG> illustrates that the determining step <NUM> includes a presenting step <NUM> of a first image for the first eye and a second image for the second eye, with the apparent distance vergence, corrected with the measured disassociated phoria, using the stereo display; wherein the first image and the second image are fusible.

<FIG> illustrates that in some implementations of the presenting step <NUM>, a fusible first image <NUM>-<NUM> can be presented on the stereo display screen <NUM>-<NUM> for the first eye <NUM>-<NUM>, and a fusible second image <NUM>-<NUM> can be presented on the stereo display screen <NUM>-<NUM> for the second eye <NUM>-<NUM>. These fusible images <NUM>-<NUM> and <NUM>-<NUM> can be peripheral. For example, the peripheral images <NUM>-<NUM> and <NUM>-<NUM> can be two, essentially identical circular bands, or rings, of balls or planets, as shown. Centers of the fusible images <NUM>-<NUM> and <NUM>-<NUM> can be shifted towards each other according to the apparent distance vergence <NUM>, the vergence angle α being corrected by the disassociated phoria δ (<NUM>), as measured in the measuring step <NUM>. The measured disassociated phoria δ can be symmetrically distributed as δ/<NUM>-δ/<NUM> between the two eyes, as shown. In these typical cases, the centers of the fusible images <NUM>-<NUM> and <NUM>-<NUM> can be shifted towards each other according to α-δ/<NUM>, the vergence angle α, corrected by the disassociated phoria δ, relative to the reference axes <NUM>-<NUM> and <NUM>-<NUM>. In response, the first eye visual axis <NUM>-<NUM> and the second eye visual axis <NUM>-<NUM> typically align with the apparent distance vergence <NUM>, corrected by the disassociated phoria <NUM>, as shown by these visual axes <NUM> pointing towards the centers of the fusible images <NUM>.

In some cases, when the binocular misalignment of the two eyes is asymmetric, the optometrist may have reasons to attribute the measured disassociated phoria δ unevenly between the two eyes. It is also noted that the earlier convention is continued to make the description more comprehensible: the description will refer to a pair of "limitation N-<NUM> and limitation N-<NUM>" simply as "limitations N", where doing so does not lead to confusion.

The shift of the fusible images <NUM> can be impacted by the accommodation optics <NUM>. The settings of the accommodation optics <NUM> can depend on L, the accommodative distance, or a spectacle power preferred by the patient, possibly further corrected by a cylinder or aberration.

In some embodiments, the fusible first image <NUM>-<NUM> and the fusible second image <NUM>-<NUM> can be dynamic. In <FIG>, the directed dashed arcs indicate that the rings of planets can be rotating around their center. Experiments have shown that making the peripheral fusible images <NUM> rotate captures peripheral prismatic effects more reliably and reproducibly. In the presenting step <NUM> the radius, spatial distribution, coloring, dynamics, and speed of rotation of these fusible images <NUM> could all be adjusted to provide the alignment information with the optimal weight.

In some embodiments, the first image <NUM>-<NUM> and the second image <NUM>-<NUM> can be static. In some embodiments, the first image <NUM>-<NUM> and the second image <NUM>-<NUM> can be central. These embodiments may present their own medical advantages.

<FIG> describes and <FIG> illustrates that the presenting step <NUM> is followed by a projecting step <NUM>. The projecting step <NUM> includes a projecting of a first added central image <NUM>-<NUM> for the first eye <NUM>-<NUM>, and a projecting of a second added central image <NUM>-<NUM> for the second eye <NUM>-<NUM>. These central images <NUM> can be projected at the center of the fusible images <NUM>. In the embodiment of fusible images <NUM> being circulating planets, the added central images <NUM> can be projected at the center of their circulation, e.g., as a cross, as shown.

The projecting <NUM> of these two added central images <NUM>-<NUM> and <NUM>-<NUM> is performed in an alternating manner, using the stereo display <NUM>. To express the alternating manner of the projecting <NUM>, only one of the added central images, the cross <NUM>-<NUM> is shown with a solid line, and the other added central image, <NUM>-<NUM> is shown with a dashed line in <FIG>. The period of the alternating can be selected according to several different criteria, and can be less than <NUM> second, in a range of <NUM>-<NUM> second, in some cases in a range of <NUM>-<NUM> seconds.

Had δ, the angle of the disassociated phoria <NUM>, measured in step <NUM>, completely captured the binocular alignments of the eyes <NUM>, then the eyes <NUM> would not have needed to adjust to the projecting step <NUM> of the added central images <NUM> with the vergence angle α, corrected by the disassociated phoria angle <NUM>/<NUM>. This would have manifested itself in that the eye visual axes <NUM> would have had remained aligned with the vergence angle α, corrected by the disassociated phoria angle δ/<NUM> after the projecting step <NUM>.

However, Applicant's studies revealed that patients moved and adjusted their eyes <NUM> in response to the projecting <NUM> of the added central images <NUM> with the corrected vergence angle α-δ/<NUM>. This led Applicant to the recognition that additional measurements were necessary to determine the remaining, residual prismatic misalignment of the eyes. These additional measurements are described in steps <NUM>-<NUM>, as follows.

<FIG> describes and <FIG> illustrates that in order to determine residual prismatic misalignments, the projecting step <NUM> can be followed by the tracking <NUM> of an adjustment of the first eye <NUM>-<NUM> in response to the projecting of the first added central image <NUM>-<NUM>, and tracking an adjustment of the second eye <NUM>-<NUM> in response to the projecting of the second added central image <NUM>-<NUM>, using an eye tracker <NUM>. <FIG> illustrates that the first eye <NUM>-<NUM> adjusts to the projecting <NUM> by rotating the first eye visual axis <NUM>-<NUM> with an adjustment angle of the first eye <NUM>-<NUM>, denoted by ε-<NUM>, and the second eye <NUM>-<NUM> adjusts by rotating the second eye visual axis <NUM>-<NUM> with an adjustment angle of the second eye <NUM>-<NUM>, denoted by ε-<NUM>. From now on, for brevity, the angles will be referenced to the apparent distance vergence corrected by the disassociated phoria, having the angle α-δ/<NUM>, instead of the reference axis <NUM>. The fact that the adjustment angles ε-<NUM> and ε-<NUM> were found non-zero, necessitated the subsequent steps of the determining step <NUM>.

<FIG> shows that the determining the accommodative convergence step <NUM> next includes projecting <NUM> a shifted first added central image <NUM>-<NUM> with a first iterative associated phoria ϕ(n)-<NUM>, to reduce the adjustment of the first eye <NUM>-<NUM>, and projecting a shifted second added central image <NUM>-<NUM> with a second iterative associated phoria ϕ(n)-<NUM>, to reduce the adjustment of the second eye <NUM>-<NUM>. Here the adjustment of the eye can be measured by a change of the adjustment angle ε(n)-<NUM>, as elaborated below.

For clarity and brevity, in this <FIG> only the first eye <NUM>-<NUM> is illustrated explicitly. The shifted added central images <NUM> are connected to the eyes <NUM> and characterized by shifted image axes <NUM>. <FIG> shows the first shifted image axis <NUM>-<NUM>, connecting the shifted first added central image <NUM>-<NUM> to the first eye <NUM>-<NUM>.

It was described in relation to <FIG> that the fixation disparity γ and the associated phoria γ*, necessary to compensate it, are not simply equal and opposite to each other. In analogy to this recognition, the associated phoria ϕ(n)-<NUM> is not simply equal and opposite to the adjustment angle of the first eye, ε(n)-<NUM>. Therefore, embodiments of the method <NUM> determine these quantities iteratively, in steps <NUM>, <NUM>,. The step index is shown in the above definitions as ϕ(n)-<NUM> and ε(n)-<NUM>: the first first iterative associated phoria is denoted with ϕ(<NUM>)-<NUM>, the first second iterative associated phoria by ϕ(<NUM>)-<NUM>, and so on. Naturally, the "-<NUM>" and "-<NUM>" indices continue to label the angles of the first eye <NUM>-<NUM> and the second eye <NUM>-<NUM>, respectively, while the "(<NUM>)", "(<NUM>)",. "(n)" indices label the first, second, and n-th steps of the iterative process.

As in the projecting step <NUM>, the projecting <NUM> of these shifted added central images <NUM>-<NUM> and <NUM>-<NUM> can be performed in an alternating manner, using the stereo display <NUM> and the computer <NUM>.

<FIG> further illustrates that the projecting step <NUM> can be followed by the tracking <NUM> of an adjustment of the first eye <NUM>-<NUM> in response to the projecting of the shifted first added central image <NUM>-<NUM>, and tracking an adjustment of the second eye <NUM>-<NUM> in response to the projecting of the shifted second added central image <NUM>-<NUM>, using the eye tracker <NUM>. Specifying the presentation to the first eye <NUM>-<NUM> only, the tracking step <NUM> includes the tracking of the adjustment angle ε(n+<NUM>)-<NUM> of the first eye <NUM>-<NUM> in response to the projecting <NUM> of the shifted first added central image <NUM>-<NUM> with the first iterative associated phoria ϕ(n)-<NUM>.

This tracking step <NUM> is analogous to the tracking step <NUM>. It is distinguished by the iterative step index having grown from (n) to (n+<NUM>). In simplified terms, embodiments of the method involve shifting the added central image <NUM> with the iterative associated phoria ϕ(n), tracking the responsive adjustment angle ε(n+<NUM>) of the eye <NUM>, determining the adjustment of the eye <NUM> from the change of the adjustment angle ε(n+<NUM>)-ε(n), and then repeating the shifting of the added central image <NUM> with a new iterative associated phoria ϕ(n+<NUM>), selected in magnitude and sign to reduce the change of the adjustment angle ε(n+<NUM>)-ε(n).

In some embodiments, the magnitude of ϕ(n+<NUM>)-ϕ(n) can be chosen to be equal to ε(n+<NUM>)-ε(n): |ϕ(n+<NUM>)-ϕ(n)| = |ε(n+<NUM>)-ε(n)|. In some cases, these embodiments may exhibit a slow convergence. Therefore, in some embodiments, |ϕ(n+<NUM>)-ϕ(n)| can be chosen to be equal to λ|ε(n+<NUM>)-ε(n)|: |ϕ(n+<NUM>)-ϕ(n)| = λ|ε(n+<NUM>)-ε(n)|, where λ < <NUM>. These embodiments often exhibit good convergence. Other, non-linear, polynomial, non-analytic or analytic relationships can also be employed in various embodiments.

After performing these steps <NUM> and <NUM> iteratively, the determining step <NUM> can be performed to determine whether an effective adjustment of the first and second eye is less than an adjustment threshold. Using the above framework, the determining step <NUM> may evaluate whether the change of the adjustment angle |ε(n+<NUM>)-ε(n)|, is less than a threshold. The effective adjustment can be defined in various ways. It can involve the change of the adjustment angle of only one of the eyes: |ε(n+<NUM>)-ε(n)| for the eye <NUM>-<NUM>; or the sum of the changes of the adjustment angles for both eyes <NUM>-<NUM> and <NUM>-<NUM>, or some weighted average, or a non-linear relation.

If the change of the adjustment angle |ε(n+<NUM>)-ε(n)| is greater than a threshold, then the method can return to the projecting step <NUM> of the shifted first added central image <NUM>, as shown in <FIG>.

On the other hand, if in step (n), the adjustment of the eye, as characterized by, e.g., the change of the adjustment angle |ε(n)-ε(n-<NUM>)|, is found to be less than the threshold, then the iteration can stop and the method can continue with the identifying <NUM> of a stabilized associated phoria ϕ from the last first iterative associated phoria ϕ(n)-<NUM>, and the last second iterative associated phoria ϕ(n)-<NUM>. Again, different formulas can be adopted to define the stabilized associated phoria ϕ in this step <NUM>, for example, ϕ = (ϕ(n)-<NUM>) + (ϕ(n)-<NUM>).

In the preceding embodiments, the disassociated phoria δ and the stabilized associated phoria ϕ were typically defined for the two eyes together. Thus, the per-eye values are half of the here-defined angles, in symmetrical cases.

The identifying step <NUM> can be followed by the identifying <NUM> of a sum of the disassociated phoria δ and the stabilized associated phoria ϕ, (δ+ϕ), as a correction to the accommodative convergence AC, with the accommodative convergence angle α, that corresponds to the apparent distance. With this, the full, or fully corrected, accommodative convergence, determined by the method <NUM>, can be expressed via the tangent of the corresponding full, or fully corrected, accommodative convergence angle: [α -(δ+ϕ)/<NUM>], in terms of prism diopters Δ. As mentioned earlier, a typical definition of the accommodative convergence is AC = <NUM> tan [α -(δ+ϕ)/<NUM>], in prism diopters Δ. This form shows one of the ways the result of embodiments of the method <NUM> is a distinct step forward compared to previous methods, where only the disassociated phoria δ was used to correct α, translating into AC = <NUM> tan [α - δ/<NUM>]. Another difference compared to previous methods is the particular system <NUM> and method <NUM>, by which δ was determined.

With the fully corrected AC having been determined by the method <NUM>, the binocular alignment can be again characterized by the AC/A ratio, the ratio of the accommodative convergence AC to the accommodative response A, to characterize the binocular alignment. This AC/A ratio can be determined for a single distance, or can be formed from AC and A values for multiple distances. For brevity, from here on, the fully corrected accommodative convergence AC will be simply referred to as accommodative convergence AC.

In some embodiments, the method <NUM> can include determining a distance vision accommodative convergence AC(Ld) as an accommodative convergence resulting from performing the method <NUM> at a distance vision apparent distance Ld; and determining a near vision accommodative convergence AC(Ln) as an accommodative convergence resulting from performing the method at a near vision apparent distance Ln.

With this preparation, in some embodiments, the binocular alignment of the first eye and the second eye can be characterized by first determining a distance vision accommodative response A(Ld) and a near vision accommodative response A(Ln), in diopters; and then by constructing a ratio of the distance vision accommodative convergence AC(Ld) minus the near vision accommodative convergence AC(Ld), divided by the distance vision accommodative response A(Ld) minus the near vision accommodative response A(Ln), to characterize the binocular alignment of the first eye and the second eye: <MAT>.

In some embodiments, the measuring <NUM> at the apparent distance and the determining <NUM> at the apparent distance can be performed using the accommodation optics <NUM>.

When the drawbacks of existing methods were described earlier, the subjectivity of the patient's feedback has been identified as one source of scatter in the data, and reason for limited reproducibility. In this context, it is mentioned that embodiments of the method <NUM> can be performed without soliciting a substantive response from the patient to determine one of the key quantities or angles. (Of course, non-substantive responses about, e.g., comfort, can very well be part of the method <NUM>. ) This is one of the keys why the method <NUM> delivers measurements with high reproducibility.

<FIG> illustrates that in some embodiments, when the method <NUM> is performed at apparent distances corresponding to near vision, the disassociated phoria and the accommodative convergence corresponding to the near vision can be determined at viewing angles below an equatorial direction <NUM> by displaying the centered images <NUM> below the equatorial direction <NUM>.

Applicant's extensive experimentation demonstrated that when prismatic eye glasses were manufactured based on the accommodative convergence determined by the method <NUM>, the patients wearing these glasses reported particularly promising reduction of digital-device related visual discomforts, pains and migraines.

It is quite likely that this substantial improvement has been achieved, among others, because the method <NUM> developed and integrated solutions regarding the points (<NUM>)-(<NUM>) identified earlier as follows.

For all these reason, the above described system <NUM> and method <NUM> offer promising new ways to reduce eye-strain related discomfort, pain and migraines.

Claim 1:
An objective method (<NUM>) to determine a binocular alignment, the method comprising:
measuring (<NUM>), via an eye tracker (<NUM>), a disassociated phoria (<NUM>) of a first eye (<NUM>-<NUM>) and a second eye (<NUM>-<NUM>) of a patient at an apparent distance; and
determining (<NUM>) an accommodative convergence of the first eye (<NUM>-<NUM>) and the second eye (<NUM>-<NUM>) at the apparent distance, characterized in that said determining (<NUM>) involves using the measured disassociated phoria (<NUM>), the determining (<NUM>) comprising:
presenting (<NUM>) a first image (<NUM>-<NUM>) for the first eye (<NUM>-<NUM>) and a second image (<NUM>-<NUM>) for the second eye (<NUM>-<NUM>), with the apparent distance vergence corrected with the measured disassociated phoria, using a stereo display (<NUM>); wherein the first image (<NUM>-<NUM>) and the second image (<NUM>-<NUM>) are fusible;
projecting (<NUM>) a first added central image (<NUM>-<NUM>) for the first eye (<NUM>-<NUM>), and projecting (<NUM>) a second added central image (<NUM>-<NUM>) for the second eye (<NUM>-<NUM>), in an alternating manner, using the stereo display (<NUM>); and
tracking (<NUM>) an adjustment of the first eye (<NUM>-<NUM>) in response to the projecting (<NUM>) of the first added central image (<NUM>-<NUM>), and tracking (<NUM>) an adjustment of the second eye (<NUM>-<NUM>) in response to the projecting (<NUM>) of the second added central image (<NUM>-<NUM>), using the eye tracker (<NUM>).