Device and method for determining aberrations or measuring optical characteristics

Abstract

The present invention relates to a device and method for determining aberrations of a lens, wherein the device (100) is characterised in that it comprises an optical system comprising, located about an optical axis (10), a light source (1); an object system (2) configured to form an image in the optical axis (10); a support means arranged in a measurement position, configured to support a test lens (5) on the optical axis (10) of the optical system, an optical unit having variable focal point (6) without axial movement and an image capturing system (7), comprising a detector (9) configured to capture the image of the object system (2) formed at the final end of the optical axis (10).

Description

[0001] DESCRIPTION

[0002] Device and method for determining aberrations or measuring optical characteristics

[0003] Technical field of the invention

[0004] The present invention falls within the field of optics. Specifically, it relates to a device and method for determining aberrations or measuring optical characteristics in optical and ophthalmic lenses, ophthalmological lenses, or multi-lens systems, including contact lenses and those used in eyeglasses and other optical aberration correction systems.

[0005] Background of the invention

[0006] Optics and optometry is an area of ​​study of special interest in the healthcare sector. It is constantly growing due to the prevalence of various types of visual defects within the population, placing increasing importance on the work of the optician-optometrist as a primary care healthcare professional. The current lifestyle is leading to an increase in certain refractive errors, such as myopia in young populations, while the aging of the population leads to an increase in presbyopia among users. A fundamental part of the optician-optometrist's work is obtaining the appropriate optical prescription for each user and providing a solution to these refractive errors. To provide users with adequate optical compensation, it is necessary to follow a methodology and use the appropriate optical-optometric equipment.An error in lens power measurement or marking results in an incorrect prescription given to the patient and, consequently, leads to user dissatisfaction due to poor visual quality. Uncorrected astigmatism or astigmatism caused by an incorrect prescription leads to reduced visual performance, which can have a functional impact, reducing the ability to perform other tasks such as reading, computer work, or driving, and can also potentially contribute to the development of asthenopia symptoms.

[0007] In this description, an optical system is defined as a system formed by a set of separating surfaces for media with different refractive indices. These separating surfaces can have multiple natures or variations, among which are ophthalmic lenses. These surfaces are traversed by a beam of rays, forming an optical axis of the system. The optical axis, in turn, is an imaginary line that defines the path along which light propagates through the system. Generally, for a system composed of simple lenses and / or mirrors, the axis passes through the center of curvature of each surface and coincides with the axis of rotational symmetry. A focused image is understood to be an image that presents characteristics or quality suitable for visualization, since it has been formed directly on the sensor or image recording medium, or the retina in the case of direct observation.In this sense, the sharpness of the optical system is understood as the contrast of the test elements against an illuminated background. In other words, sharpness is the quality of an image that indicates clarity or distinction in the reproduction of details, related to resolution and contrast. Its determination may or may not require user intervention.

[0008] In addition to sharpness, other criteria can be used to determine the quality of the resulting image. In this sense, blurriness is understood as the quality of an image given by the lack of sharpness. Image details cannot be clearly resolved or distinguished from the background. Additionally, the edges of a digital image can be defined as transitions between significantly different gray levels, also known as discontinuities. They provide valuable information about object boundaries and can be used for image segmentation, object recognition, etc. Most edge detection techniques employ local operators based on different discrete approximations of the first and second derivatives of the image gray levels. On the other hand, the magnification of an optical system is the aspect ratio of the image size relative to the object size.It can be calculated as the image size divided by the object size. The dioptric power of a lens or optical system is defined as the inverse of the focal length of the element, or set of elements, expressed in meters. This focal length is calculated with respect to the principal planes of the lens, which are not visible physical elements. Therefore, in the fields of ophthalmics, ophthalmology, and optometry, the back vertex dioptric power is often used, where the distance from the image focus of the lens is taken from the back vertex of the lens rather than from the principal image plane.

[0009] The determination of optical characteristics, such as the posterior vertex dioptric power of ophthalmic lenses, is fundamental and crucial in the process of refractive error compensation. Currently, the most widely used devices in optometric offices for measuring dioptric power are fronto-focometers. A fronto-focometer, or fronto, is an instrument for measuring the dioptric power of lenses. Its function is based on determining the posterior vertex power of a lens, commonly used for refractive error compensation, in addition to marking the lens positioning. Two main types of fronto-focometers are available on the market: manual (more affordable and widespread) and automatic models (40% more expensive) with different capacities and features.

[0010] Conventional manual frontos use a test that the user must focus by observing it through the eyepiece, and the observer manually adjusts the adjustable dioptric power wheel to achieve this goal. When measuring a spherical lens (without astigmatism), it is inserted into the fronto in the designated position, and through the eyepiece, the observer perceives the defocus of the T test uniformly. The T test is refocused using the fronto's power wheel, yielding a dioptric power result when a sharp, focused image is achieved, where the T test elements can be resolved by the user. On the other hand, when the lens being measured is astigmatic, the T test image defocuses unevenly depending on the lens power in each meridian.For the refocusing of the T test in this second case, it is necessary to focus each of the test blades in two independent measurements that are performed following the same method as with a spherical lens with the addition of the orientation of the T test on the main meridians of the lens.

[0011] The final result will be a composition between the results obtained for each of the principal meridians (tangential planes of a lens or optical system where the extreme values ​​of dioptric power are found), with which a series of steps must be carried out until obtaining the spherical-cylindrical notation commonly used in the practice of optometry and in the manufacture of ophthalmic lenses. These steps that must be carried out until obtaining the spherical-cylindrical notation can present a series of derived problems such as: possible confusion when noting the orientation of the measured meridians, long measurement time, the subjectivity of the measurement and the dependence of the result on the ametropia of the observer, in short, as it is a completely manual and subjective process, there are a set of factors that can inherently affect the measurement performed.Unfortunately, these types of errors can occur relatively frequently when using this type of fronto. On the other hand, automatic fronto, while free from these drawbacks by directly providing the final measurement result with little user intervention, are based on complex technologies (wavefront sensors, aberrometers, etc.) and, consequently, are more expensive than manual ones.

[0012] Therefore, in summary, while the manual frontofocometer is based on the axial displacement of the test within the optical system to obtain the dioptric power of the lens in the different meridians, the automatic frontofocometer is based on other optical principles such as aberrometry, which increases its price compared to manual ones. Some examples of this type of solution, protected by patent applications, can be found in the documents described below.

[0013] Document US10976217B2 refers to a high-resolution image capture apparatus for a lens, allowing the LED light head to illuminate the lens and capture an image of it seen through a saline-filled cuvette. According to this solution, an image is first captured with zero optical power, and then the image is captured with the contact lens inside the cuvette, capturing an image through the lens suspended in the alkaline solution. Through this comparison, the optical power of the lens is calculated. Alternatively, document US2002140928 discloses an apparatus for measuring the optical properties of ophthalmic lenses. Said document describes a solution where a reference image is created and the optical properties of the lens are measured.The measurement is performed based on the displacement of the reference image from a base position in which the lenses are not deposited in the system compared to a measured position in which the path traveled by the rays of the optical system includes said lenses. On the other hand, document US2018106700 describes systems and methods for determining optical parameters of ophthalmic lenses. This document includes means for processing an image of an object captured through the lenses, determining said optical characteristics based on, at least, that image. For its part, document US2007121 100 refers to a system for measuring the characteristics of ophthalmic lenses, including optical power. However, said apparatus consists of an image capture and processing system, polarizing filter(s), a ray reflection system, lens and a mirror inclined at 45°. e. Document WO2018178493 discloses a method for designing ophthalmic lenses and an apparatus for measuring their optical characteristics. The invention comprises: positioning an object at a certain distance; a reference frame for the user for each eye, keeping one eye uncovered and covering the other; a screen that is placed in front of the eye with a through hole, moving the position of the hole until said object is seen through the hole. Subsequently, the positions of the holes are adjusted to achieve binocular vision and design each lens according to said position. Application WO2019002656 describes a device for measuring the optical power of optical testing systems (4).The device includes an optical object generating assembly (2), a support (3) for the optical testing system, a digital image detector and a deflector assembly (6) intended to produce lateral displacement of the initial optical image (41), such that a displaced optical image (61) and another reference optical image (60) are generated. The digital image detector (5) captures both images in at least one that contains data on the lateral displacement, calculating from them and by means of processing means the optical power of the system to be tested (4). Finally, document ES2171474 presents an apparatus for measuring the refractive index of a crystal such as a lens for glasses without the need to measure the surface geometry of the crystal.Including: a) a source of a spatially coherent beam of radiation; b) a beam splitter for supplying a sample beam and a reference beam; c) a translatable retroreflector that reflects the reference beam; d) a holding device; e) a detector that evaluates the reflected reference and sample rays in order to produce a detector output signal; and f) an analyzing element that determines the refractive index of the material in response to the position of the translatable reflector and the thickness of the material.

[0014] On the other hand, there is also research related to this type of solution. For example, the document "A New Calibration Method for the Dioptric Power of Intraocular Lenses" discloses a series of methods for obtaining dioptric power in intraocular lenses: calculation from measured dimensions, determination from the measured posterior focal length, and determination from the measured magnification. The document "Refractive index distribution and optical properties of the isolated human lens measured using magnetic resonance imaging (MRI)" presents a noninvasive MRI technique for measuring the distribution of the refractive index from the crystalline lens, performing a mapping of the crystalline lens. This publication describes focal length measurements obtained by the propagation of simulated light rays through the lens.

[0015] Finally, a variable-focus optical unit can be defined as a lens or set of lenses where, as its name suggests, the focus can be modified. An example of this type of lens can be seen in "Electrowetting Lenticular Lens for a Multi-View Autostereoscopic 3D Display," which shows a lens system incorporated into autostereoscopic 3D displays based on electrowetting. These lenses allow the lens focal length to be adjusted by applying electrical voltage. In other words, fluidic lenses based on electrowetting actuation are attractive due to their wide focal adjustment range, but they are limited by optical aberrations, either intrinsic to the lenses themselves or due to the optical imaging systems in which they are used.However, the ability to control the shape of the meniscus that forms the refractive surface of the lens with a high degree of spatial precision will allow for the correction and compensation of a wide range of these aberrations. There are variable-power lenses based on electrowetting, for example, the opto-fluidic lens, or TOFU lens, for Tunable Opto Fluidic Unit. Some lenses are controlled by only four electrodes, which limits the generation of astigmatism in orientations other than these. Alternatively, there are lenses controlled by 32 electrodes placed azimuthally, for which most aberrations up to the fourth radial Zernike order can be corrected. This lens is tunable by the action of a voltage change. Examples of this type of lens can be found developed in application EP3123213A1.

[0016] Additionally, it is worth highlighting document KR 20060000999 A which describes an optical system for an automatic lens meter for measuring the refractive power of a lens. The system comprises a light source (10), a collimating lens (20), an expanding concave lens (40) and a convex lens (65). The collimating lens (20) is in the form of a convex lens installed at a predetermined focal length from the light source, such that the measuring light beam generated from the light source (10) is transmitted and propagates in parallel.The expanding concave lens (40) is installed at the rear of the object lens (30) so that the horizontal measuring light beam passing through the collimating lens (20) expands with respect to the optical axis after passing through the object lens (30), and reaches a disk or diaphragm (50) in which a plurality of openings (55) are formed at a predetermined angle on a circumference to disperse the measuring light beam passing through the expanding concave lens (40) into a plurality of smaller beams. The convex lens (65) allows the measuring light beam passing through the disk (50) to be converged on the optical axis, and the plurality of openings (55).A typical optical system is provided for an automatic lensmeter, further comprising a prism lens (60) installed immediately behind the aperture opening (50) and comprising a plurality of prisms (66) corresponding to the apertures, and a focusing lens (70) installed behind the prism lens (60) so as to redirect / focus the light beam from the aperture and passing through the prism lens (60) onto a two-dimensional sensor array (80). Specifically, the system describes the use of prisms and apertured disc to determine the power of a test lens, using a subsequent operation unit for determining the reference position of the beam and the position after introduction of the test lens.

[0017] However, it is worth noting the limitations existing in the comparison of the image captured after including the problem lens in the optical axis as described in this document.

[0018] Currently known solutions present at least one of the following limitations when determining aberrations or measuring optical characteristics (such as dioptric power) in optical and ophthalmic lenses:

[0019] - High influence on the part of the professional handling the device.

[0020] - Existing devices have large dimensions

[0021] - Low portability

[0022] - Low measurement capacity in determining the different types of existing aberrations

[0023] Increasing precision involves high complexity and cost

[0024] - Low or no sharpness measurement capacity

[0025] Therefore, it is necessary to develop new solutions for determining aberrations or measuring optical characteristics in optical and ophthalmic lenses.

[0026] Summary of the invention

[0027] The object of the present invention is to provide a solution to the problems currently encountered in determining aberrations or measuring optical characteristics in optical and ophthalmic lenses. Specifically, in a first aspect, the present solution relates to a device for determining optical characteristics in optical and ophthalmic lenses, including contact lenses and those used in eyeglasses or other optical aberration correction systems. Specifically, the present solution relates to a device for determining aberrations, for example, the prismatic effect, or measuring optical characteristics, both spherical and astigmatic, comprising a variable-focus optical unit such as, for example, a TOFU lens.

[0028] Thus, the device comprises an optical system comprising the following elements: an illumination source, an object system, a support medium, a variable focus optical unit, and an image capture system.

[0029] These elements are arranged consecutively, forming an optical axis starting at the illumination source and ending at the image capture system. However, the position of the support means can be modified along the optical axis formed. The illumination source is configured to illuminate along the optical axis, in the direction of the object system. The object system is located after the illumination source and is the object to be clearly visualized in the plane where the image capture system is located. To this end, the object system comprises a test so that the sharpness of an image can be measured and defined. Additionally, the device comprises a means for supporting a test lens. Said support means is configured to support an ophthalmic lens, the test lens, in a measuring position on the optical axis formed.A problem lens is understood to be a lens whose characteristics are to be determined.

[0030] The variable focus optical unit is a variable dioptric power element capable of generating high-order aberrations through electronic control of the voltage applied to the electrodes comprising it, which allows the curvature of an interface of liquids contained within it to be changed. That is, the variable focus optical unit comprises a refractive liquid interface capable of generating, unlike other previous solutions, sphero-cylindrical dioptric power, where said interface comprises a set of tunable actuation zones. Said tunable set allows the curvature of the interface of the variable focus optical unit to be modified, altering its behavior. To this end, the variable focus optical unit comprises a control element configured to modify at least one actuation zone of the interface of the variable focus optical unit.In this way, modifying the curvature of the refractive liquid interface of the variable-focus optical unit can compensate for the effect generated by the inclusion of a problem lens in the optical axis of the device, and said modification can be used to determine the optical characteristics of the problem lens. Finally, to determine the success of the curvature modification in the variable-focus optical unit, the device comprises an image capture system. Said image capture system comprises a detector configured to capture the test image of the target system. This image capture system is configured to digitize the image captured by the detector, sending it to an associated image processing system. This processing system is configured to compare the sharpness of the image captured by the detector and the initial sharp image from the test.Additionally, the processing processing system is configured to send a signal to the variable focus optical unit controller element.

[0031] Therefore, the device is initially configured and calibrated such that the target system can be clearly visualized on the image capture system's detector. That is, the inclusion of a variable-focus optical unit in an optical system such as the one described allows the image of an object system to be focused on the image capture system, depending on the sharpness of the captured image. By adjusting the curvature of the variable-focus optical unit, the image generated in the image capture system's detector plane is sharp and can be used as a reference image. However, when the target lens is placed, in use, on the support medium provided for this purpose in the measurement position, the image appears out of focus. Compensation for this inclusion can be achieved solely by adjusting the curvature of the variable-focus optical unit.Since there is no need to modify the distance between lenses, as is the case with known solutions, a compact device is achieved.

[0032] Unlike other previous solutions, such as comparing the position of light beams, the presence of a test in the target system makes it possible to define the sharpness of an image formed in the capture system and to use this characteristic during the adjustment of the variable focus optical unit. In this way, a final refocusing state can be defined, where the final image is once again sharp. In other words, the system according to the present invention provides an alternative for obtaining results regarding the determination of aberrations and the measurement of a characteristic of a problem lens, whether spherical or astigmatic.

[0033] In a second aspect of the invention, the solution relates to a method for determining aberrations or measuring an optical characteristic of a lens or lens system. First, the device according to the present invention is arranged, calibrating the variable focus optical unit so that the image formed on the detector of the test image capture system is clearly visible. To do this, the curvature of the variable focus optical unit can be adjusted so that the image plane resulting from the device's optical system coincides with the detector, such that the captured image is clear. The user of the device then places a test lens on the support means configured for this purpose, resulting in a blurred image on the detector plane of the image capture system. To refocus the image, the curvature of the variable focus optical unit is acted upon.The result of modifying the curvature of the variable-focus optical unit's interface is a shift in the plane where the image of the object system is formed, allowing the image to be refocused on the plane where the image capture system's detector is located, ensuring image sharpness. That is, the final image captured by the detector of an image capture system, once refocusing is complete and the curvature of the variable-focus optical unit is adjusted, is a fully focused image, both spherically and astigmatically. Finally, once refocusing has been performed, the curvature modification can be determined to refocus the image sharply, compared to the initially adjusted curvature, and thus correlate the modification of this curvature with an optical characteristic of the problem lens, for example, the lens' dioptric power.

[0034] Therefore, the proposed solution presents a device and method for determining aberrations and measuring an optical characteristic of a lens, for example, an ophthalmic lens, based on compensation by a variable-focus optical unit for the blur produced by the problem lens. This is an economical solution, requiring little effort or influence from the professional handling the device. Additionally, it is a precise solution with a compact configuration, requiring little space, which increases its portability, as axial displacement of the elements is not required.

[0035] In the figures of the present invention, reference is made to the following set of elements: 100 Device for determining an optical characteristic

[0036] 1 Lighting source

[0037] 2 Object system

[0038] 3 Condenser lens 4 Test

[0039] 5 Problem lens

[0040] 6 Variable focus optical unit

[0041] 61 Interface

[0042] 62 Set of action zones

[0043] 7 Image capture system

[0044] 8 Focusing lens

[0045] 9 Detector

[0046] 10 Optical axis

[0047] Brief description of the figures

[0048] Figure 1 shows a schematic of an embodiment of a device for determining an optical characteristic of a problem lens.

[0049] Figure 2 shows a schematic of one embodiment of a variable-focus optical unit comprising an interface and a set of actuation zones formed by 32 electrodes. Figure 3 shows a schematic of the detailed arrangement of one embodiment of a variable-focus optical unit between the test and the image.

[0050] Figure 4a-4m shows a photograph of an out-of-focus image (left) after fitting a test lens of a) 8.00 D, b) 6.00 D, c) 4.00 D, d) 2.00 D, e) 0.75 D, f) 0.50 D, g) 0.00 D, h) -0.50 D, i) -0.75 D, j) -2.00 D, k) -4.00 D, i) -6.00 D, m) -8.00 D and a refocused image (right) after readjustment of the variable focus optical unit according to the first example.

[0051] Figure 5 shows a photograph of the image of a reference lens (A), and an out-of-focus image (left) after the placement of nine problem lenses (B) L10, (C) L1 1, (D) L12, (E) L13, (F) L14, (G) L15, (H) L16, (I) L17, (J) L18, and a refocused image (right) after readjustment of the variable focus optical unit according to the second example.

[0052] Detailed description of the invention

[0053] In a first aspect of the invention, a device (100) is described for determining aberrations or measuring an optical characteristic. As shown in Figure 1 , the device (100) comprises an optical system formed by: an illumination source (1 ), an object system (2), a support medium, a variable focus optical unit (6), and an image capture system (7), which comprises an associated image processing system. The illumination source (1 ) is responsible for generating a beam of rays that run along the optical axis to illuminate the object system (2). This illumination system (1 ) can have various configurations.

[0054] Thus, in a first embodiment, the illumination source (1 ) is an illumination source with condensing or converging optics. In this embodiment, the illumination source (1 ) comprises a condenser lens (3) configured to direct the beam of rays generated by the illumination source (1 ) to a test (4), comprised in the object system (2), located after the condenser lens (3). Alternatively, the illumination source (1 ) is an illumination source with collimating optics. In this embodiment, the illumination source (1 ) comprises a collimating lens, which directs the beam of rays generated by the illumination source (1 ) to a test (4) of the object system (2). Unlike other previous solutions, based on light beams, the presence of a test (4) makes it possible to determine the complete focus of said beams by means of the sharpness of the image on the detector.In this way, it is possible to determine the spherical and astigmatic power of a problem lens (5).

[0055] The support means is arranged in a measuring position and is configured to support a test lens (5) on the optical axis (10) of the optical system. The measuring position where the support means is located may vary. Thus, in a particular embodiment, the measuring position is located between the object system (2) and the variable focus optical unit (6). Alternatively, the use of a measuring position arranged between the variable focus optical unit (6) is also acceptable. The effect of including a problem lens (5) in both embodiments generates the alteration of the optical formation on the optical axis (10), defocusing the resulting image in the detector plane (9).

[0056] For its part, as can be seen in Figure 2, the variable focus optical unit (6) comprises, firstly, a tunable refractive liquid interface (61 ). That is, the variable focus unit (6) comprises a set of action zones (62) configured to modify the curvature of the interface (61 ), so that the interface (61 ) has the capacity to generate sphero-cylindrical dioptric power. Thus, the set of action zones (62) produce a spherical, cylindrical or sphero-cylindrical effect depending on, for example, the distribution of the electrical tension (voltage) for each of the individual action zones, so that said characteristics of a problem lens (5) introduced into the device (100) can be determined.

[0057] In a particular embodiment, the interface is tuned via electrowetting. Thus, the set of actuation zones (62) is tunable via electrowetting. Alternatively, other tuning means may be used, such as mechanical deformation of a membrane (actuated by pressure and / or torsion, among others), dielectric elastomers, or even sound or temperature control, which are currently under development. In an alternative embodiment, the interface (61) may be tuned by using pressure membranes.

[0058] Additionally, said variable focus optical unit (6) comprises a control element configured to modify at least one area of ​​action of said set of areas of action (62). The variation in the set of areas of action of the variable focus optical unit (6) generates a modification of the curvature of the interface (61) comprised in said variable focus optical unit (6), creating a refractive surface with characteristics specifically defined by the user.

[0059] In a particular embodiment, the set of actuation zones (62) comprises at least two pairs of actuation zones. Specifically, in a more particular embodiment, the set of actuation zones comprises a total of 32 actuation zones distributed or electrodes in 16 pairs of opposing actuation zones. In this way, at least 16 meridians can be configured on which the variable focus optical unit (6) acts.

[0060] Optionally, the support half can be configured to act simultaneously as a cover for the variable focus optical unit (6) and as a platform for placing the problem lens (5). An example of this type of support half is a 3D part designed for this purpose. In this particular configuration, the measurement position where the problem lens (5) is placed is placed as close as possible to the variable focus optical unit (6), avoiding vignetting effects in the case of using convergent lighting.

[0061] Finally, the image capture system (7) comprises a detector (9). The detector (9) is configured to capture the image formed by a test (4) of the object system (2). Additionally, the image capture system (7) may comprise a focusing lens (8), such that the detector (9) is located in the image plane of said focusing lens (8). The image capture system (7) is configured to digitize the resulting image captured by the detector (9). Said digitization allows for subsequent processing by the individual or automatic processing by a computer. Alternatively, direct observation, without digitizing, may require the use of other shaping elements, such as a lens that enlarges the size of the image on a recording medium, such that a greater measurement error would be incorporated, including the human error of the user of this device.

[0062] The use of a variable focus optical unit (6) in a device (100) such as the one described in the present solution allows the adjustment of the focus of the image formed on the detector (9) without the need to use movable elements, or other equivalent means, where additional space is required to make an adjustment in the focus of the image.

[0063] The inclusion of an external lens, or problem lens (5), in the support medium of a previously focused device (100), defining a sharp initial image of the test (4), can generate a blur of the image in the plane on which the detector (9) of the image capture system (7) is located. In this way, analyzing the dioptic power, the absence of blur after the inclusion of the problem lens (5) implies that the optical axis (10) has not been modified by said inclusion, so that the problem lens (5) is a flat lens, without the capacity for modification. However, the generation of blur due to the inclusion of a problem lens (5) indicates that said problem lens (5) has a dioptic power different from 0, whether spherical or cylindrical.

[0064] As indicated above, the variable focus optical unit (6) has the ability to focus the image by varying the curvature of the inference (61). Therefore, by modifying the curvature of the variable focus optical unit (6) through the control element, the image is readjusted in the image plane where the detector (9) of the image capture system (7) is located, giving rise to a new sharp image.

[0065] Although the controller element can be actuated by the user, it is recommended that the controller be actuated automatically, which eliminates errors.

[0066] In order to be able to actuate the controlling element automatically, the device (100) comprises an image processing system, associated with the capture system (7). Said image processing system is configured to calculate and send a corresponding signal to the controlling element of the variable focus optical unit (6) so that at least one area of ​​action of said variable focus optical unit (6) is modified, resulting in the variation of the curvature of said variable focus optical unit (6). As indicated, the modification of the curvature of the variable focus optical unit (6) manages to compensate, in contrast to previous solutions, both the spherical and astigmatic components of the problem lens (5).

[0067] Said image processing system is a feedback system, as it is configured to emit an actuating or activating signal to the variable focus optical unit controller element (6) based on the result of the image processing. According to this characteristic, the system can perform a series of iterations, sending a signal to the image processing controller element, until obtaining a completely sharp and focused image of the test (4), with a sharpness similar to the initial sharp image obtained prior to the inclusion of the problem lens (5). In this way, the interaction of the user of the device is limited exclusively to the inclusion of the problem lens (5) in the support medium of the device (100). The processing system is configured to perform a numerical analysis of the image focus based on metrics such as sharpness.In turn, the final magnification can be determined by the magnification of the image in the different orientations to guide the compensation in sphero-cylindrical lenses in the direction of the orientation of the cylindrical component or the sign of the power (positive or negative).

[0068] In summary, the processing system may be adapted to calculate or correlate the lens power from the curvature of the variable focus optical unit (6). In an alternative, the processing system may further comprise means configured for the use of machine learning or application of artificial intelligence, in the processing of the image towards the final adjustment measurement.

[0069] The use of a device (100) of reduced size and appropriate characteristics for the purpose set allows the use of shorter focal length lenses and that in turn, unlike current solutions, makes it possible to reduce the size and increase practicality, in an economical way for the user.

[0070] The variable focus optical unit (6) can be characterized with a Hartmann-Shack aberrometer, measuring the wavefront generated by said variable focus optical unit (6) as a function of the curvature it presents. Said characterization of the variable focus optical unit (6) provides information on the spherical and astigmatic dioptric power (low order aberrations) generated by the component, but also information on high order aberrations that may or may not be used in the subsequent measurement on a problem lens (5). That is, the prior calibration of the variable focus optical unit (6) used allows a broader characterization of the analyzed problem lens (5), by also being able to determine Zernike coefficients, which may contain more interesting information about the optical surface, beyond the dioptric power with which one usually works, at an ophthalmological and optometric level, in the compensation of refractive errors.Currently, there are other means that can alternatively perform this characterization. That is, characterization using other aberrometers or wavefront sensors would also be acceptable.

[0071] In a second aspect of the invention, a method is described for determining the aberrations of a problem lens (5). Said method comprises the following steps:

[0072] - arranging a device (100) as described above, calibrating the variable focus optical unit (6) so that the image formed on the detector (9) of the image capture system (7) is a clear image of the test (4) of the object system (2) of the device (100),

[0073] - arranging a problem lens (5) in the support means of the device (100), giving rise to a blurred image in the detector plane (9) of the image capture system (7).

[0074] - refocus the image obtained on the detector plane (9) by acting on the curvature of the interface (61) of the variable focus optical unit (6), again obtaining a clear image of the test (4);

[0075] - determining the modification of the curvature of the interface (61) of the variable focus optical unit (6) generating the sharp image; and

[0076] - correlate the modification of the curvature of the variable focus optical unit (6) with an optical characteristic of the problem lens (5).

[0077] In a further embodiment, the measurement and compensation of the blur of the problem lens (5) can be carried out automatically, by means of an image processing system. In this way, the refocusing of the image comprises the steps of computer analyzing the image, sending a signal to the controlling element of the variable focus optical unit (6) and acting on the curvature of the interface (61). In this way, the image processing can define an iterative process, automatically feeding back until a focused image is obtained on the detector (9) of the device (100). For this purpose, a numerical analysis of the image based on metrics such as sharpness, final magnification, blurriness, among others, can be performed.In turn, the final magnification can be determined by the magnification of the image in the different orientations to guide the compensation in sphero-cylindrical lenses in the direction of the orientation of the cylindrical component or the sign of the power (positive or negative).

[0078] In particular, an automatic image focus can be defined that includes:

[0079] I. a spherical power sweep modifying the dioptric power of the set of action zones (62), defining an interface (61) comprising a spherical curvature generating a locally sharp image;

[0080] II. an orientation sweep modifying the dioptric power, in a separate and orderly manner, in a localized manner in the different meridians of the spherical interface (61) of stage I, defining an interface (61) comprising an initial sphero-cylindrical curvature with an objective axis, maintaining the spherical curvature of stage I;

[0081] III. an astigmatism sweep by modifying the dioptric power of the interface (61 ) according to stage II, giving rise to an interface (61 ) comprising a target sphero-cylindrical curvature keeping the spherical curvature generating the locally sharp image fixed according to stage I, and the target axis defined in stage II, where the target sphero-cylindrical curvature comprises a target power such that it refocuses the image.

[0082] Optionally, a final spherical adjustment sweep can be performed by varying the power of each area of ​​action, resulting in a sharp final test image (4), with a sharpness similar to the sharp initial test image (4). Alternatively, the order of these steps can be modified according to a person skilled in the art. For example, obtaining a target axis can be obtained prior to characterizing the spherical curvature.

[0083] A locally sharp image can be understood as a sharp image in one of the meridians existing in the interface (61 ). This local sharpness is achieved by defining a spherical curvature, obtained through the set of action zones (62) of the interface (61 ), which compensates for the spherical power produced by the problem lens (5). According to this method, we can define a spherical curvature as that curvature of the interface that produces spherical dioptric power. In contrast, a sphero-cylindrical curvature is that curvature where the dioptric power produced comprises both a spherical and astigmatic effect.

[0084] In this way, an initial sphero-cylindrical curvature can be defined as that curvature which partially compensates for the sphero-cylindrical power introduced by the problem lens (5). That is to say, the initial sphero-cylindrical curvature allows to define an objective axis, as that axis defined by a subset of action zones (62) of the device which compensates for the astigmatism of a locally sharp image, obtained by the compensation of the spherical part.

[0085] On the other hand, orientation is used in image processing because the shape of the beam, circular for the experimentally validated implementation, suffers an oval deformation in the presence of astigmatism, and the orientation of said ellipse (angle formed with the horizontal by the longest axis of the ellipse) can be associated with the orientation of the astigmatism. In this way, a target axis can be defined.

[0086] Finally, the target sphero-cylindrical curvature is that curvature that comprises a target sphero-cylindrical power. Thus, the target power is that power that defines a new curvature of the set of action zones (62) of the interface (61) so that it compensates for the modification generated by the incorporation of a problem lens (5) in the optical axis. That is, as can be seen in this method, the action zones (62) can be modified to compensate for the spherical and cylindrical effect of a problem lens (5) introduced into the device (100), and thus determine these characteristics of the problem lens (5) when the image is refocused.

[0087] By way of example, in a particular embodiment where the set of action zones is defined by a set of electrodes, the final result of the image processing is a combination of voltages for the different electrodes that produce at the interface the curvature that re-forms the image on the detector (9) clearly, regardless of the type of problem lens (5), that is, whether the problem lens is spherical or introduces astigmatism. Regardless of the process, manual or automatic, used for image processing or adjustment of the curvature of the variable focus optical unit (6), the final image taken by the detector (9) is a totally focused image, in all directions.

[0088] However, the use of an automatic image processing system can make it unnecessary to view the image during the process, reducing the number of elements that make up the device (100). This differs from other solutions currently used, for example, the observation made in a manual frontofocometer for an astigmatic lens requires focusing each of the main meridians separately, with only one direction of the test being focused each time a measurement is made.

[0089] Therefore, a device (100) and a method are achieved that allow the determination of an optical characteristic of a problem lens (5), both the spherical and astigmatic components. The proposed device (100) allows the optimization of the elements, reducing their dimensions, thereby improving the practicality and portability of the described device. The method by which the lens measurement is obtained is easily understood by the user who uses the device, without needing extensive knowledge in aberrometry or interferometry. Additionally, a device can be designed that achieves the determination automatically. That is, user interaction during the calibration and focusing of the image is avoided.

[0090] A first example of implementation of this solution has been made with the following components:

[0091] - Lighting source (1) comprising: Thorlabs brand green LED (505nm), and a condenser lens (3): Achromatic doublet with focal length f'i = 100 mm, Linos brand.

[0092] - An object system (2) comprising: a test (4) contact grid of 26 mm diameter. This is a circular object in which the upper half is concentric lines separated by 1 mm, while the lower half is a radial scale of angles.

[0093] - Variable focus optical unit (6) comprising a 32-electrode TOFU lens, according to the dimensions in Table 1:

[0094] Table 1. Dimensions of the device between the test and the image according to example 1

[0095] - Image capture system (7) comprising a focusing lens (8), achromatic doublet with focal length fó b= 40 mm, Edmund Optics model 47665; and a detector (9), IDS UI-3582LE-C (AB00488). It is a CMOS sensor that has a resolution of 2560x1920 pixels (4.92 Mpx), 15.2 fps, and 2.2 pm pixel size.

[0096] Figure 3 shows a schematic of part of the device, specifically from the test to the detector, without showing the illumination system. This schematic shows an arbitrary test lens, the TOFU lens (central element), and an achromatic doublet that acts as a focusing lens on the sensor.

[0097] Additionally, to carry out this example, an image processing system was used. Specifically, in this case, a computer with Matlab software was used.

[0098] This example of the solution's implementation focuses the test image (4) on the detector (9) when the focal length of the TOFU lens is 105 mm, equivalent to approximately 9.5 D.

[0099] From this initial position, whose curvature is known, as well as the voltages that generate said curvature, the measurement of the problem lens (5) will be obtained from the curvature modification values ​​to refocus the image on the sensor when a problem lens (5) is included in the measurement position (12.5 mm prior to the TOFU lens). Additionally, for the control of the TOFU lens, an image processing has been programmed received in the sensor of the image capture system. On the image received in the sensor, different combination criteria are applied, based on blurring, edge detection and magnification. As indicated previously, the processing system can be adapted to carry out an analysis from a set of criteria, the sharpness measurement being the most important.

[0100] Specifically, the image processing system may employ the size and eccentricity of the blurred image when the problem lens (5) is introduced relative to the reference image captured by the detector (9). These factors may serve as a guide to establish a starting curvature of the variable focus optical unit (6).

[0101] To do this, the processing system is able to compare said size with a database containing blurred images generated by different ophthalmic lenses of known dioptric power, which allows the size of the blurred image to be correlated with the power of the spherical equivalent or blur M of the problem lens (5) introduced, where M = S + C / 2, with S being the value of the sphere and C the value of the cylinder. Although it is not an exact measurement, it provides an approximate starting value M.

[0102] Additionally, the eccentricity of the test image on the detector (9) allows the processing system to estimate the presence and orientation of the astigmatism, since the circular test image can take an elliptical shape and the size relationship between both meridians can be correlated with the pure astigmatism of the system, so that the range in which the next iteration is performed can be fine-tuned. Additionally, the orientation of said ellipse is related to the orientation of the astigmatism. As in the previous step, the approximation made by the eccentricity is not an exact measure, but it allows defining or improving a first iterative value.

[0103] With the previously estimated starting value M, the processing system can perform a sweep of the purely spherical power required to refocus the resulting image through the input of the problem lens (5). Specifically, it acts by varying each of the TOFU lens electrodes equally, modifying the curvature of the interface. To do this, the value M can be translated into voltage V M consulting the characterization of the variable focus optical unit (6), and a variation, manual or automatic, of the voltage is carried out in a range centered on V Mso that the curvature of the variable focus optical unit is modified as the voltage varies. The width of this range can be estimated by the eccentricity, so that the eccentricity is related to an estimated value of J, where J = C / 2. The range is determined by the interval M ± J, which is translated to voltage V and multiplied by a factor 1.75. In the case of a range in voltages less than 0.75 V, a range of 0.75 V is set. In this initial spherical sweep, the detector (9) captures the image for each combination of voltages and the sharpness for the new image is computed until the point of best image quality is found, which will correspond to the voltages that allow the image to be focused. The calculation of the sharpness for this case has been carried out with the intensity gradients of the image collected by the detector (9).For example, if 30 different voltage values ​​are generated, one image is taken for each voltage value, and the sharpness of that image is calculated, resulting in 30 voltage-related sharpness values. Sharpness will increase to a point of improved image quality because, thanks to the previous criteria, it will be possible to determine the curvature that focuses the image blurred by the problem lens being measured.

[0104] This method of operation by scanning and calculating sharpness can then be performed for an orientation scan, an astigmatism scan, and optionally, a spherical final adjustment scan.

[0105] I. Orientation sweep: Using the interface curvature value, a curvature modifying voltage can be estimated, related to the astigmatism J detected in the eccentricity measurement. Thus, the voltage is decreased in a single meridian (corresponding to a pair of action zones (62a, 62b) of the array or, in a particular embodiment, two opposite electrodes) but the orientation of this meridian is rotated. This translates into decreasing the voltage of two opposite electrodes starting from an orientation of 0 e up to 180 e . One of the orientations is expected to give greater image quality (sharpness), and this would select the orientation of the astigmatism, objective axis, of the lens.

[0106] II. Astigmatism scanning: in the orientation chosen in the previous step, that is, maintaining the target axis, the set of action zones (62) is varied, for example, by modifying the voltage of the electrodes that form it. The voltage variation is carried out from 0 D of astigmatism to twice the astigmatism J estimated from the eccentricity. To do this, it is centered on the calculated value of the eccentricity, for example, ± equivalent to 0.75 D. For various voltage values, the sharpness of the resulting image is calculated and the voltage of the image with the best sharpness is chosen. As a final check, a spherical scan is carried out again in which each action zone is varied equally, for example, the voltage of each electrode, starting from the voltage value obtained in the astigmatism scanning step. Again, the curvature values, or curvature-modifying voltage, that give the sharpest image among those obtained in the scan are chosen.

[0107] The combination of all the voltages gives a sharp image in all orientations, with a sharpness similar to the initial test image (4), prior to the entry of the problem lens (5). Obtaining a sharp image in all directions, unlike previously known solutions, is the sign that the test image is being formed on the detector (9) and that the curvature of the variable focus optical unit (6) given by these voltages compensates in the dioptric power introduced by the problem lens (5), both spherical and astigmatic, (so a different measurement should not be made for each meridian where the main powers are located).

[0108] The processing system can then determine the power of the problem lens (5). In accordance with a particular embodiment, the voltages of the 32 electrodes of the actuation zones (62) can be obtained, such that they form a sinusoidal function that can be related to the dioptric power profile of the lens, relating the voltages with the characterization. That is, said power is not obtained directly from the voltages, or in general the curvature, of the variable focus optical unit (6) but some calculations are necessary applying paraxial optics together with the characterization of the variable focus optical unit (6) and / or the use of a look-up table with standard lenses.

[0109] In summary, the processing system may be adapted to calculate or correlate the lens power from the curvature of the variable focus optical unit (6). In an alternative, the processing system may further comprise means configured for the use of machine learning or application of artificial intelligence, in the processing of the image towards the final adjustment measurement. In addition, axial displacements of the elements beyond the change in power of the tunable lens are not necessary, such that the space required for the system is smaller and more compact.

[0110] The use of a device (100) of reduced size and appropriate characteristics for the purpose set allows the use of shorter focal length lenses and that in turn, unlike current solutions, makes it possible to reduce the size and increase practicality, in an economical way for the user.

[0111] The result of this image processing is a response that modifies the voltage of the TOFU lens towards higher or lower values ​​at the local level of each of the 32 electrodes that generate the curvature of the interface (61).

[0112] Figures 4a-4f and Figures 4h-4m show a photograph of an out-of-focus image (left) after inserting a problem lens (5) - from -8 D to +8 D, in steps of 2 D, as well as lenses of ± 0.75 D and ± 0.50 D - and a refocused image (right) after readjustment of the TOFU lens. Figure 4g shows the result in the reference position, i.e. in the absence of the problem lens. Therefore, the incorporation of a problem lens (5), other than 0.00 D, in the support means of the device (100) produces a certain blurriness. This blurriness is corrected by adjusting the TOFU lens, which compensates for the action of the problem lens (5), and the final image when compensation has been made with the TOFU lens and therefore the measurement, based on the spherical power of the problem lens (5) indicated by the manufacturer.

[0113] Thus, the results of the measurements carried out on test lenses (5), from a test box of known spherical power from -8 D to +8 D, in 2 D steps, as well as lenses of ± 0.75 D and ± 0.50 D, show that good sensitivity can be achieved, even at lower power values. The results in vector Fourier notation are shown in Table 1 . In this case, since they are spherical lenses, the conventional notation is not included because the sphere in this case is equivalent to the M value for each case. Furthermore, in the second column from the left, the voltage necessary to act on the TOFU lens and focus the test image (4) on the detector (9) is included. In the previous case, the maximums and minimums have been included because, since these are lenses with astigmatism, an astigmatic surface must be created, for which, at a local level, certain meridians (pairs of electrodes) will have higher or lower voltage.In the case of spherical lenses, the creation of a spherical surface does not require these differences in the electrodes; they all act proportionally.

[0114] Table 2. Frontal dioptic power results

[0115] Additionally, a simulation was performed using Zemax on stereocylindrical lenses based on ophthalmic lens manufacturing parameters. The parameters were chosen to be as similar to real lenses as possible, although the environment in which these measurements were performed was a digital simulation. Likewise, the cylinder axis in these lenses was simulated for different orientations.

[0116] The results obtained according to the simulation are shown below in Table 3 and 4.

[0117] Table 3 shows the frontal power results for the stereocylindrical test lenses: the theoretical results based on the radii of curvature, refractive index, and thickness; and the frontal power measured from the interface curvature in the TOFU lens. It is represented in rectangular Fourier notation, which allows for accurate statistical processing of differences. The first column of this table shows the average, maximum, and minimum voltages used to obtain the curvature given by the simulation. Additionally, Table 4 shows the prescription of the simulated lenses and the measured values ​​in spherocylindrical notation.

[0118] Table 3. Frontal dioptric power results from the simulations, in rectangular Fourier notation.

[0119] L1 Average 103.447 M -0.124 -0.141 AM 0.017

[0120]

[0121] Table 4. Results of measurements on simulated ophthalmic lenses represented in conventional notation (sphere, cylinder and axis)

[0122] The differences obtained in frontal power result in averages of 0.022 ± 0.010 D in the Zemax measurements and -0.007 ± 0.018 D in the experimental measurements. The maximum differences are 0.036 D and 0.075 D, for the Zemax and experimental measurements, respectively. Since the minimum step between powers typically used in patient refraction is 0.12 D, the voltages obtained by both methods are similar and follow the behavior expected by the TOFU lens, where the manufacturing tolerances of the TOFU lens are taken into account.

[0123] For example, the reference position requires a voltage of 104.147 V in the simulations and 105.548 V in the experimental measurements. Although these values ​​are different, the difference can be explained by tolerances and falls within a range between the ±0.50 D powers of the test box lenses. Calibration with lenses of known power would allow this reference point to be further fine-tuned, and the voltage jumps that allow the curvature to be recreated follow a predictable pattern. For example, in the case of spherical lenses, the voltage increase is approximately linear.

[0124] A second embodiment of this solution has been carried out with the following components. The experiment has been carried out with the following components

[0125] Illumination source (S) comprising a green LED (505 nm) Thorlabs brand, and a condenser lens (L1), achromatic doublet with focal length f'i = 100 mm, Linos brand.

[0126] - Object system (2) comprising a Test (4), 26 mm diameter contact reticle. - Variable focus optical unit (6) comprising a 32-electrode sphero-cylindrical TOFU lens according to the dimensions in Table 5.

[0127] Table 5. Dimensions of the device between the object (test) and the image, according to example 2.

[0128] - Image capture system (7) comprising a focusing lens (8), achromatic doublet with focal length f¿ b = 40 mm, Edmund Optics model 47665; and a detector (9), IDS UI-3582LE-C (AB00488). It is a CMOS sensor that has a resolution of 2560x1920 pixels (4.92 Mpx), 15.2 fps, and 2.2 pm pixel size.

[0129] Additionally, to carry out this example, an image processing system based on Matlab software has been used again.

[0130] In this second example, measurements were taken on nine sphero-cylindrical ophthalmic lenses (L10-L18), from different manufacturers and with different refractive indices. The main difference between the two experiments is the use of two different TOFU lenses. As can be seen in Tables 1 and 5, there are differences in the dimensions and the order of the refractive indices. These differences must be present when translating the voltages applied to the lens into dioptric power, as well as other differences in the dimensions of the device, but both lenses follow the same operating principle. From each problem lens, voltages are obtained that recreate a refractive inference that places the focal planes of the system on the sensor after the lenses have displaced them. These voltages, when passed through the calibration values ​​with the Hartmann-Shack aberrometer and the paraxial optics calculations, allow the dioptric power of the problem lens to be obtained.The results are shown in Table 6 and 7.

[0131] Table 6. Results of dioptric power measurements in sphero-cylindrical ophthalmic lenses.

[0132] Table 7. Results of voltage measurements for each of the lenses.

[0133] Figure 5 shows a photograph of an out-of-focus image (left) after the placement of nine problem lenses L10 - L18 and a refocused image (right) after readjustment of the variable focus optical unit according to the second example.

[0134] Therefore, performing two experiments with different variable-focus optical units serves as a demonstration of the experiment's repeatability. Regarding the measurements performed, the main difference between the two experiments is that Example 1 shows experimental measurements of spherical lenses (in addition to simulated results), while Example 2 provides experimental measurements with sphero-cylindrical lenses, with both spherical and astigmatic power. In other words, this device can be used to determine aberrations in astigmatic lenses.

Claims

A device for determining lens aberrations, wherein the device (100) is characterized in that it comprises an optical system comprising, located around an optical axis (10); or an input illumination source (1) configured to illuminate along an optical axis (10) in the direction of an object system (2), or an object system (2) configured to form an image on the optical axis (10) where the object system (2) comprises a test (4) defining a sharp initial image; or a support means arranged in a measurement position, configured to support a problem lens (5) on the optical axis (10) of the optical system, or a variable focus optical unit (6) without axial displacement comprising ■ an inferred (61) refractive liquid with the capacity to generate stereo-cylindrical dioptric power in the meridians of the variable focus optical unit (6), ■ a set of tunable action zones (62) configured to modify the curvature of the interface (61), and ■ a controller element configured to modify at least one area of action (62) of the interface (61) of the variable focus optical unit (6); and an image capture system (7), comprising a detector (9) configured to capture the image of the test (4) of the object system (2) formed at the end of the optical axis (10) and digitize the image captured by the detector (9); and an image processing system, associated with the capture system (7), configured to compare, in use, the sharpness of the image captured by the detector (9) and an initial sharp image of the test (4) and send a signal to the controller element of the variable focus optical unit (6), modifying at least one area of action of said variable focus optical unit (6), in a reiterative manner until a sharp image of the test (4) is obtained. The device according to claim 1, wherein the illumination source (1) is an illumination source with condenser optics. 3.- The device according to claim 1, wherein the illumination source (1) is an illumination source with collimating optics. 4.- The device according to any one of claims 1 to 3, wherein the measuring position is arranged between the object system (2) and the variable focus optical unit (6). 5.- The device according to any one of claims 1 to 3, wherein the measurement position is arranged between the variable focus optical unit (6) and the detector (9) of the image capture system (7). 6.- The device according to any one of claims 1 to 5, wherein the set of action zones (62) is tunable via electro-humidification. 7.- The device according to any one of claims 1 to 6, wherein the set of actuation zones (62) comprises at least two pairs of actuation zones (62a, 62b). 8.- The device according to any one of claims 1 to 7, wherein the image capture system (7) comprises a focusing lens (8), and a detector (9) located in an image plane of said focusing lens (8).

9. The device according to any one of claims 1 to 8, wherein the image processing system is configured to perform a numerical analysis of the focus.

10. Method for determining aberrations of a lens, where the method is characterized in that it comprises: - arranging a device (100) according to any one of claims 1 to 9, calibrating the variable focus optical unit (6) so that the image formed on the detector (9) of the image capture system (7) is a clear image of the test (4) of the object system (2) of the device (100); - arranging a problem lens (5) in the support means, giving rise to a blurred image in the detector plane (9) of the image capture system (7); - refocusing the image by acting on at least one area of action of the interface (61) so that the curvature of the interface (61) is modified, obtaining a sharp image again; - determine the modification of the curvature of the interface (61) generating the sharp image; and - correlate the modification of the curvature with an optical characteristic of the problem lens (5).

11. Method according to claim 10, wherein the method comprises an automatic refocusing of the image comprising: I. a spherical power sweep modifying the dioptric power of the set of action zones (62), defining an interface (61) comprising a spherical curvature generating a locally sharp image; II. an orientation sweep modifying the dioptric power, in a separate and orderly manner, in a localized manner in the different meridians of the spherical interface (61) of stage I, defining an interface (61) comprising an initial sphero-cylindrical curvature with an objective axis, maintaining the spherical curvature of stage I; III. an astigmatism sweep by modifying the dioptric power of the interface (61 ) according to stage II, giving rise to an interface (61 ) comprising a target sphero-cylindrical curvature keeping the spherical curvature generating the locally sharp image fixed according to stage I, and the target axis defined in stage II, where the target sphero-cylindrical curvature comprises a target power such that it refocuses the image.

12. Method according to claim 11, wherein the method further comprises a final spherical adjustment sweep, varying the voltage of each area of action, resulting in a clear final image of the test (4).

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