100 of FIGS. 3A-F which have a shared refraction 143, only the shared channel 141 needs to cover the wide range of refractions, and the first channel 111 and second channel 121 only need to cover a narrow differential refraction which is the narrow refraction difference between the first refraction 113 and the second refraction 123, presented to the patient as the comparison steps or intervals. This refraction can vary in a much narrower range, such as a defocus range of −1D to +1D. Therefore, in such shared refraction embodiments of the multi-channel subjective refractor 100, only the optical elements in the shared channel 141 cover the wide range of sphere and cylinder powers, and are therefore expansive and expensive, while the small and narrow-range optical elements in the first channel 111 and second channel 121 cover only the much-narrower differential refraction range, and are therefore small and much less expensive. Such shared refraction embodiments therefore offer benefits for an optometry practice.

In an example, the shared channel 141 can be configured to cover a wide defocus range of −20D to +20D, while both the first channel 111 and the second channel 121 can be configured to cover only the narrow differential defocus range of −1D to +1D. In another example, the shared channel 141 can be configured to cover the wide defocus range of −20D to +20D, the wide cylinder power range of −10, or −15, cylinder D to +10, or +15, cylinder D, and the wide cylinder angle range from 0 to 180 degrees, whereas the first channel 111 and the second channel 121 can be configured to cover only the differential defocus range of −1.5D to +1.5D and the differential cylinder power range of −1 cylinder D to +1 cylinder D. Similarly, in some embodiments of the multi-channel subjective refractor 100 at least one of the first channel defocus CD1, the first channel cylinder CC1, the second channel defocus CD2 and the second channel cylinder CC2 are all less than two diopters, where “diopter” refers inclusively to both sphere and cylinder diopters.

Of course, in some embodiments of the multi-channel subjective refractor 100, at least one of the first channel 111 and the second channel 121 can cover wide diopter ranges. For example, at least one of the first channel defocus CD1 and the second channel defocus CD2 can cover a range of +/−15 D, in some cases +/−20 D and at least one of the first channel cylinder CC1 and the second channel cylinder CC2 can cover +/−10 D, in some cases +/−15 D.

A further simplification can be achieved in some embodiments of the multi-channel subjective refractor 100 by using a design where one of the first channel 111 or the second channel 121 is not configured to refract the corresponding first image 110i or second image 120i at all. In such embodiments, one of the first refraction 113 or the second refraction 123 simply equals the shared refraction 143, and the differential refraction is generated only by the other, refracting channel. Finally, in some embodiments, different portions of the differential refraction can be implemented in different channels. For example, the differential defocus can be implemented only in the first channel 111 as CD1, but not accompanied by a differential channel cylinder (i.e. CC1=0), while the differential cylinder is implemented in the second channel 121 as CC2, wherein the second channel 121 does not have any defocus: CD2=0.

FIGS. 3B-F show several embodiments of such “shared-refraction plus distributed differential refraction” designs. In particular, FIG. 3B shows an embodiment where the first channel 111 is only refracts the first image 110i with a first channel cylinder CC1 via a first stokes lens 116, while the second channel 121 is configured to refract the second image 120i with a second channel defocus CD2 via a second translational stage 125 that moves the second display 120 along the axis. In some cases, the second channel 121 can further include a second stokes lens 126 to also refract the second image with a second channel cylinder CC2, as shown. In this embodiment, the shared channel 141 includes a shared movable lens 144 to refract both images with a shared defocus SD, but not with a shared cylinder SC. The summary refraction table reads as:

shared + channels

first defocus
D1 = SD + 0

first cylinder
C1 = 0 + CC1

second defocus
D2 = SD + CD2

second cylinder
C2 = 0 + CC2

FIG. 3C shows another exemplary embodiment of the multi-channel subjective refractor 100, where the shared channel 141 includes both the shared movable lens 144 to refract the first and second images 110i/120i with the shared defocus SD, and a shared stokes lens 146 to refract the first and second images 110i/120i with a shared cylinder SC. In addition, the first channel 111 has the first stokes lens 116 to refract the first image 110i with the first channel cylinder CC1, and the second channel 121 has a second movable lens 124 to refract the second image 120i with the second channel defocus CD2. The corresponding refraction table reads as:

shared + channels

first defocus
D1 = SD + 0

first cylinder
C1 = SC + CC1

second defocus
D2 = SD + CD2

second cylinder
C2 = SC + 0

FIG. 3D shows yet another implementation of the multi-channel subjective refractor 100. Here the shared channel 141 again includes the shared movable lens 144 to refract the first and second images 110i/120i with the shared defocus SD, and also includes the shared stokes lens 146 to refract the first and second images 110i/120i with a shared cylinder SC. The first channel 111 has the first stokes lens 116 to refract the first image 110i with the first channel cylinder CC1, and the second channel has the second translational stage 125 to translate the second display 120 to refract the second image 120i with the second channel defocus CD2. FIG. 3D shows that in this description the term “lens” is used in a broad, inclusive way to refer to any lens assembly that satisfies the overall function of a lens. Lens assemblies are often used in place of individual lenses to optimize the system performance in face of other challenges. These include, for example, the need to reduce chromatic aberration by using a crown-flint doublet in place of a single lens as the shared movable lens 144, as shown in FIG. 3D. These lens assemblies are also referred to as achromats, or as cemented doublets. Other lens assemblies may be used to increase contrast sensitivity or to reduce thermal expansion coefficients. The refraction table once again reads:

shared + channels

first defocus
D1 = SD + 0

first cylinder
C1 = SC + CC1

second defocus
D2 = SD + CD2

second cylinder
C2 = SC + 0

FIG. 3E shows yet another embodiment of the multi-channel subjective refractor 100. The main difference relative to FIG. 3D is that in the second channel 121, the second channel defocus CD2 is generated by a second variable power lens 127, instead of the second movable lens 124, or the second translational stage 125 for the second display 120. There is a wide and growing selection of innovative variable power lenses 127. These include fluid filled lenses, where the curvature and therefore the power of the lens is varied by controlling the amount and possibly the spatial distribution of the fluid by applying pressure, or pumping fluids from fluid reservoirs. Variable power lenses 127 can also be formed with suitably engineered and spatially distributed liquid crystals where the focus is varied with applying an external voltage. Yet other solutions may also be used, like Alvarez lenses, where two optical elements with a cubic or more complex profile are rotated relative to each other. Some embodiments may achieve the effect of variable power by using a deformable mirror. The refraction table of FIG. 3E is the same as for FIG. 3D, as shown.

Finally, FIG. 3F shows yet another embodiment of the multi-channel subjective refractor 100. This again has the shared movable lens (assembly) 144 to refract the first and second images 110i/120i with a shared defocus SD, and the shared stokes lens 146 to refract the images with a shared cylinder SC. The first channel 111 includes a first translational stage 115 to translate the first display 110 to refract the first image 110i with the first channel defocus CD1, and the first stokes lens 116 to refract the first image 110i with the first channel cylinder CC1. The second channel 121 includes the second translational stage 125 to translate the second display 120 to refract the second image 120i with the second channel defocus CD2. In addition, this embodiment may include a compensator plate 128 that can be included to compensate higher order aberrations or chromatic aberrations that emerge between the first image 110i and the second image 120i because they propagate through different optical elements. This embodiment includes translational stage 115 and 125 in both channels, and thus contains more degrees of freedom than minimally required. Such redundant elements in this and in earlier-described embodiments may be included to provide added control and to further minimize unwanted optical effects, such as chromatic aberrations or higher order aberrations. The refraction table for the embodiment of FIG. 3F reads as:

shared + channels

first defocus
D1 = SD + CD1

first cylinder
C1 = SC + CC1

second defocus
D2 = SD + CD2

second cylinder
C2 = SC + 0

The above-described large number of embodiments of the multi-channel subjective refractor 100 are examples of configuring the first channel 111, the second channel 121 and the shared channel 141 to enable an independent adjustment of the first refraction 113 and the second refraction 123. Before moving on, it is also mentioned that embodiments of the multi-channel subjective refractor 100 can be collimating, as the multi-channel subjective refractor 100 can image the displays 110/120 to infinity. Typically, this effect is achieved by emitting a collimated beam through an exit pupil towards the eye 1 of the patient, as shown with the tracing of the first and second image rays 110ir and 120ir. Further, in some simple optical designs, the projected size of the objects may change as the focus is changed. However, this can lead to an error in the patient's perception as a larger image is often perceived as “clearer” by a patient. Some embodiments of the multi-channel subjective refractor 100 preempt this problem by making use of an optics (first channel 111, second channel 121 and shared channel 141) that is telecentric, and thus the apparent size of the projected object (images 110i/120i) does not change with a changing of the focus. Other embodiments do not need such a telecentric optic, as the size of the images 110i/120i can be also changed electronically on the displays 110/120.

It is mentioned that recently a new class of intraocular lenses has been introduced that are light adjustable non-invasively after implantation. For these light adjustable lenses (LALs), the optometrist performs a refraction measurement after the implantation to measure the difference of the refraction of the implanted LAL from the planned, or patient-preferred refraction. These differences are typically small, typically in the 0.5 D-1.5 D range. Therefore, some embodiments of the multi-channel subjective refractor 100 that are intended to be used only in conjunction of the LAL adjustment procedure, can be made much smaller, since the movable lenses 114/124/144 and the translational stages 115/125 need to cover only the limited range of optical refractive powers of about −2 D to +2 D, instead of the general purpose refractors that typically cover much wider ranges up to −20 D to +20 D. Smaller multi-channel subjective refractors 100 with limited measurement and adjustment ranges naturally cost less, and thus can bring the medical benefits of the LAL to a wider range of patients.

For completeness it is mentioned that in embodiments where the covered diopter range is wider, additional optical design elements may need to be introduced. For example, if the first channel 111, the second channel 121, or the shared channel 141 is designed to cover a wide diopter range of −10D/+10D, then the beam may need to be deflected out by a mirror toward a Porro prism, from where the returning beam is reflected back into the channel by a second mirror. In some designs, the Porro prism can provide coverage for the −10D/+10D diopter range by being moved by 3-5 inches on a moving stage.

FIGS. 4A-B show that embodiments of the multi-channel subjective refractor 100 can be configured to present the first image 110i with the first refraction 113 and the second image 120i with the second refraction 123 simultaneously as an up-down image pair (FIG. 4A), or a side-by-side image pair (FIG. 4B), or any other positioning of an image pair. Corresponding to these presentation types, multi-channel subjective refractors 100 can also be called dual field refractors, simultaneous refractors, parallel refractors, or side-by-side refractors. The presented images can be of a wide variety, including actual photos and pictures, or a line of a Snellen chart, or individual letters, for example the often used capital E, or any kind of eye chart, or a log MAR chart, or an armed force target. The patient's communication may be made clearer by attaching a label to the first image 110i and the second image 120i, e.g. the letters A and B in FIG. 4A.

While the electronics of the multi-channel display 100 clearly enables the first display 110 and the second display 120 to generate different first and second images 110i and 120i, the patient may find comparing identical images with different refractions easier. Also, showing the same line of an eyechart only with different refractions for comparison is the practice optometrists have been following historically. Therefore, in many embodiments of the multi-channel subjective refractor 100 the first image 110i and the second image 120i may be the same, and can include one or more letters of an eye chart, of a Snellen chart, of an army target, or any other figure of an examination chart, which is not necessarily alphanumerical.

FIGS. 4A-B show clearly a key aspect of the multi-channel subjective refractor 100: that the patient is presented simultaneously, in parallel, with the images to be compared. The images are separated not in time, but only in space. As discussed, such refractors 100 (1) eliminate the mental, cognitive pressure on the patient to keep the memory of the visual clarity of previous images active; (2) enable a more accurate comparison because the two images are presented simultaneously and can be directly compared; (3) eliminate the frustrating repeated “back and forth” requests by patients to the optometrist/OD; and (4) greatly reduce the chair time, or time in the lane, because the comparison proceeds much faster, thereby substantially improving the workflow and economy of the optometrist office.

The process of exploring the relevant refraction space can be further accelerated by designing multi-channel subjective refractors 100 that include one or more additional channels, configured to present one or more additional images (beyond the first and second images 110i/120i) with corresponding refractions simultaneously for the eye. Such multi-channel subjective refractors 100 can thus present three, four, or more images simultaneously for the patient, who is then prompted to choose the sharpest image from the three, four or more images.

Here we make some comparative remarks. As known, the human eye refracts light with different wavelengths with slightly different indices of refraction. This is called dispersion, or chromatic aberration. The changing refractive index causes the optical power to change with wavelength. The difference of the eye's optical power between red and green light is approximately 0.5 D in the human eye. As a consequence, if the red component of an incoming light is focused on the retina, then the green component is focused about 0.2 mm in front of the retina. This fact is used in the so-called duochrome eye tests, when half of the black letters on the optical chart are presented over a red background and half of them over a green background. The effect of the eye's chromatic aberration or dispersion is that if the letters over the red background appear sharp, then the letters over the green background will appear blurry; and vice versa. The underlying theory is that the red and green wavelengths project objects that have an effective difference in refraction of about 0.5 D between them. The red and green colors are approximately symmetric on either side of the yellow color, thought to be key to optimize vision. Therefore, the patient is presented by a sequence of lenses and asked whether the letters over the red or green background appear sharper. The optometrist keeps changing the lenses until equal sharpness is achieved for the letters over the red and green backgrounds, which is taken as a sign that the yellow light is best focused on the retina.

This duochrome test is qualitatively different from the here-described method in several aspects. (1) The duochrome device presents two letters with equal optical power, or refraction, for the eye whereas embodiments of the multi-channel subjective refractor 100 present two letters with different refractions.

(2) In the duochrome test, the apparent difference of refractions is not generated by the device, but by the eye's chromatic aberration only, whereas embodiments of the multi-channel subjective refractor 100 do not rely on the eye's chromatic aberration as they typically present the letters over a white background.

(3) The duochrome test is useless for pseudophakic eyes with implanted diffractive IOLs, because those IOLs has minimal or negligible chromatic aberration. Some non-diffractive IOLs can also have lower chromatic aberration. In contrast, the multi-channel subjective refractor 100 can be very helpfully utilized to refract eyes with IOLs, especially light adjustable IOLs (LALs), where the refraction is an important step of the post-operative lens adjustment.

(4) The goal of the duochrome test is to achieve the patient reporting equally clear vision of the presented two letters, whereas a goal of the multi-channel subjective refractor 100 is the patient reporting one letter being clearer than the other one. Often, it is easier to notice and report a visual difference than to conclude that the visions of two eyes are equally clear.

(5) The duochrome test is not capable of testing and measuring cylinder.

(6) The duochrome method cannot easily change the difference between the two presented refractions unless the wavelengths are changed. The chromatic aberration between 550 nm (green) and 650 nm (red) is approximately 0.5 D. If one wanted to change the power difference, the wavelengths of the projections would have to be changed (for example by changing pigments in the ink or changing the emissive source of an electronic display), which is generally not easy to do with standard materials.

(7) Patients may be confused when presented with objects of two different colors and asked to specify the clearer one. One color may be more pleasant than the other or may appear “brighter” to the patient, influencing the patient's choice. Also, eyes are naturally more sensitive to green wavelengths than red, leading to another potential source of error.

(8) Neural detection and processing differences between green and red signals within the retina and optic nerve may also lead to a source of error in the measurement.

(9) Red-and-green duochrome methods won't work well if the starting state of the refractor is not already close to the patient's prescription. Far away from the ideal refraction, picking the sharper image may be difficult and error-prone for the patient. For this reason, duochrome methods are primarily used only for a potential “final adjustment” of refraction after the refraction has already largely been determined.

Some of these differences are well demonstrated in embodiments of the multi-channel subjective refractor 100, where the first display 110 generates the first image 110i with approximately or precisely the same background color as the second display 120 generates the second image 120i, while the first refraction 113 is different from the second refraction 123.

Yet another distinctive aspect of the multi-channel subjective refractor 100 is that it enables evaluating and optimizing vision experiences for patients at patient-preferred distances as part of prescribing glasses, or determining LAL adjustments. Some patients prefer optimized near vision, at distances of about 40 cm, others optimized distance vision at 6 meters, but in office settings it is more and more customary to optimize vision at intermediate distances, such as at 60 cm-70 cm. In a traditional optometrist lane, the measurement distances are fixed, whereas with the multi-channel subjective refractor 100 the optometrist can simulate the visual experience at any distance according to the patient's preference.

FIG. 5 shows that some embodiments of the multi-channel subjective refractor 100 can provide a refractor for each eye, thereby forming a binocular multi-channel subjective refractor 100b. Each of the individual multi-channel subjective refractors 100L and 100R for the left and right eyes, respectively, of this binocular refractor 100b can use or employ any of the previously described embodiments of the multi-channel subjective refractor 100.

FIG. 6 further shows that such a binocular multi-channel subjective refractor 100b can be implemented as a head-mounted binocular multi-channel subjective refractor 100h, which, again, can utilize any previously described embodiment of the individual multi-channel subjective refractor 100.

FIG. 7 shows that the operation of the multi-channel subjective refractor 100 can be partially or fully automated. A few, or several, or all steps of the operation of such automated refractors 100 can be automated, and therefore can be carried out by a lesser trained technician, or possibly even by the patient herself. Naturally, such automation can further reduce the chair time, or demand on the optometrist's lane, and thus can have multiple beneficial effects on the optometry practice. Such automated refractors 100 enable the patient herself to explore the refraction parameter space away from the chair or lane, in a preparation or waiting area. This allows the patient to take all the time needed to repeatedly try out various refractions, possibly for longer periods and allow her eyes to accommodate to the presented refractions. Such unhurried, self-guided refraction measurements with the multi-channel subjective refractor 100 may increase the accuracy and reliability of the eventually chosen optimal refraction.

Some embodiments of such an automated multi-channel subjective refractor 100 may include an automated refraction control system to receive an input from the patient; and to change at least one of the first refraction 113 and the second refraction 123, in response to the patient input. In more detail, the multi-channel subjective refractor 100 may include a user interface 152 to receive a patient input 154; a multi-channel subjective refractor controller 156, to generate a refraction change signal 157 in response to the patient input 154; at least two of a shared actuator 158-S, a first channel actuator 158-1 and a second channel actuator 158-2, coupled to the multi-channel subjective refractor controller 156, to change a corresponding refraction in response to the refraction modification signal 157.

In an example of the operation, the multi-channel controller 100 may present the letter E with a first refraction 113 of 2.0 D, and with a second refraction 123 of 2.5 D for an eye 1, as shown in FIG. 4B, side by side, and the patient may be prompted to create a patient input 154 by indicating which letter is sharper. Having received this patient input 154, the multichannel refractor controller 156, or simply refractor controller 156, can generate a refraction change signal 157 to increase or to decrease the first or second refraction 113/123 presented to the patient.

The patient can generate the patient input 154 in many different ways. The patient input 154 can be verbal, i.e. saying out loud which is the sharper image, and the corresponding electric control input can be generated by the optometrist, or a technician, by selecting a refraction change on a graphical user interface of the user interface 152. In these semi-automated designs, the role of the refractor controller 156 is only to generate a refraction change signal 157 that corresponds to the entered refraction change. In other semi-automated embodiments, the user interface 152 can have dials, knobs, sliders, or any other types of input devices, and the patient can be prompted to turn a knob to create a refraction change command for the refractor controller 156. In this case, the refractor controller 156 again only generates a refraction change signal 157 that corresponds to the refraction change command by the patient, to make the actuators 158-S, 158-1 and 158-2 to carry out the corresponding refraction changes.

In other, fully automated designs, the user interface 152 can be a voice recognition system that understands the verbal patient input 154 and translates it for the refractor controller 156. The patient input can be only which image 110i or 120i appeared sharper for the patient, but may not specify a refraction change value. In these designs, the refractor controller 156 can have a (search) algorithm installed in a processor, or computer, 156-p that actually determined what refraction change is most reasonable given the patient input 154.

In any of the above embodiments, the user interface 152 can be one of a graphic user interface, a voice recognition and control interface, a motion sensor, and an at least partially mechanical interface, including one of a slider, a knob, or a switch.

As discussed, the automated multi-channel subjective refractor 100 can be partially or fully automated. In non-automated traditional refractors, the refraction change is typically created by mechanical changes, e.g., by moving lenses in or out of the optical pathway mechanically.

In partially (semi-) automated multi-channel subjective refractors 100, the refraction change can be partially electronic. For example, the user interface 152 can be a voice recognition system, and the refractor controller 156 is tasked to convert the voice-recognized command into the electronic refraction change signals 157. These refraction change signals 157 eventually can actuate an electromotor that causes the translation of the first or second displays 110/120 along their translational stages 115/125, or move the movable lenses 114/124/144, or rotate the lenses of the stokes lens 116/126/146.

In some embodiments, the multi-channel subjective refractor 100 can be fully automated by including the optional processor 156-p, to scan a relevant refraction parameter space efficiently by executing a search algorithm; and to change the corresponding refraction according to the search algorithm. The refraction parameter space can include at least three dimensions: the defocus/sphere/optical power, the magnitude of the cylinder, and the direction of the cylinder. The latter two can be reparametrized as the cylinder in the 0 degree and in the 45 degree direction, or in the x and y direction. In more complex embodiments of the multi-channel subjective refractor 100, the refraction search space can be spanned by more than three dimensions.

Including the processor 156-p can be very useful, because the mere patient input 154 that, e.g., “the first image 110i with the first refraction 113 appeared sharper than the second image 120i with the second refraction 123”, does not determine unequivocally how to change the refraction. There can be more than one refraction changes that are well-motivated by the same patient input 154. As it is well known, naïve “brute force” scanning search algorithms can be very inefficient. There are now textbooks dedicated to how to accelerate and to improve the efficiency of search algorithms. The search algorithm, coded and stored in a computer-readable medium, in conjunction with the processor 156-p can be any of these optimization algorithms, such as convex optimization, conjugate gradient methods, genetic codes, neural network codes, linear, binary, hashing algorithms, artificial-intelligence-based algorithms, or any other search algorithm. Such search algorithms can change two or even three refraction parameters simultaneously, which enable search process on the multi-channel subjective refractor 100 to converge to the optimal refraction much faster than the naïve scanning methods.

In some embodiments, the multi-channel subjective refractor 100 can also potentially present a series of letters at different resolutions at the end of the refraction process to the patient to read off (or type) using the determined refraction, in order to get another measure of the patient's best corrected visual acuity.

FIG. 8 shows a method 200 of operating the multi-channel subjective refractor 100. The method 200 can include the steps of:

- generating 210 a first image 110i with a first refraction 113 and a second image 120i with a second refraction 123 with the multi-channel subjective refractor 100;
- presenting 220 the first image 110i with the first refraction 113 and the second image 120i with the second refraction 123 simultaneously for an eye 1 of a patient by the multi-channel subjective refractor 100; and
- prompting 230 the patient to identify the sharper of the first image 110i and the second image 120i.

This description of the method steps already captures a distinguishing factor of the refractor 100 and the method 200: that the first and second images 110i and 120i are presented in parallel, simultaneously for the patient.

The generating step 210 and the presenting step 220 can be carried out by the various embodiments of the multi-channel subjective refractor 100, as described in FIGS. 1-7 above. The prompting step 230 can be carried out either verbally by a medical technician or a doctor, or in an automated fashion, e.g. by a voice command generated by the multi-channel subjective refractor 100 itself. As is reasonable, in either of these cases, the patient should be given the necessary time to make a considered choice.

FIG. 9 shows in some detail that in the method 200 the generating 210 can comprise generating 210-1 the first image 110i with a first display 110; generating the second image 120i with a second display 120; refracting 210-2 the first image 110i by a first channel 111 with a first channel refraction 112; refracting the second image 120i by a second channel 123 with a second channel refraction 112; receiving 210-3 and combining the first image 110i and the second image 120i by a beam combiner 130; receiving 210-4 the first image 110i and the second image 120i