ES3033817A1 - Device and method for determining aberrations or measuring optical characteristics - Google Patents

Abstract

The present solution relates to a device and method for determining lens aberrations, wherein the device (100) is characterized in that it comprises an optical system comprising, located around an optical axis (10); an illumination source (1); an object system (2) configured to form an image on the optical axis (10); a support means arranged in a measurement position, configured to support a problem lens (5) on the optical axis (10) of the optical system, a variable focus optical unit (6) without axial displacement and an image capture system (7), comprising a detector (9) configured to capture the image of the object system (2) formed at the end of the optical axis (10). (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

Device and method for determining aberrations or measuring optical characteristics

Technical field of the invention

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.

Background of the invention

Optics and optometry is an area of study of special interest in the healthcare sector, and one that 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 healthcare professional. The current lifestyle is leading to an increase in certain refractive errors, such as myopia in young populations, and the aging of the population is leading to an increase in presbyopia among users. A fundamental part of the work of the optician-optometrist 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 appropriate optical-optometric equipment. An error in measuring the power of the lenses or in their marking leads to an incorrect prescription given to the patient and, consequently, generates user dissatisfaction due to poor visual quality. Uncorrected astigmatism or astigmatism caused by a poor prescription leads to reduced visual performance, which can have a functional impact, reducing the ability to perform other tasks such as reading, working at a computer, or driving, as well as potentially contributing to the development of asthenopia symptoms.

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 may have multiple natural surfaces, including ophthalmic lenses. These surfaces are traversed by a beam of rays, forming the 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 viewing, since it has been formed directly on the sensor or image recording medium, or on 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. That is, 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.

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 local distance of the element, or set of elements, expressed in meters. This focal distance is calculated with respect to the principal planes of the lens, which are not visible physical elements, so, in the field of ophthalmics, ophthalmology and optometry, the posterior vertex dioptric power is usually used, where the distance of the lens image focus is taken from the posterior vertex of the lens instead of from the principal image plane.

Determining optical characteristics, such as the posterior vertex dioptric power of ophthalmic lenses, is fundamental and crucial in the process of compensating for refractive errors. 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 compensating for refractive error, in addition to marking the lens position. 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.

Conventional manual frontos use a test that the user must focus by observing through the eyepiece, and the observer manually adjusts the variable 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, giving 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.

The final result will be a composite of the results obtained for each of the principal meridians (tangential planes of a lens or optical system where the extreme dioptric power values are located). A series of steps must be taken to obtain the sphero-cylindrical notation commonly used in optometry and ophthalmic lens manufacturing. These steps, which must be taken to obtain the sphero-cylindrical notation, can present a series of problems, such as: possible confusion when recording the orientation of the measured meridians, long measurement times, the subjectivity of the measurement, and the dependence of the result on the observer's ametropia. In short, since it is a completely manual process, there are a number of factors that can inherently affect the measurement. Unfortunately, these types of errors can occur relatively frequently when using this type of frontos.

On the other hand, automatic frontos, while not presenting these drawbacks by directly providing the final measurement result with little intervention in the process by the user, are based on complex technologies (wavefront sensors, aberrometers, etc.) and, consequently, are more expensive than manual ones.

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.

Document US10976217B2 refers to a high-resolution image capture apparatus for a lens, allowing the LED light head to illuminate the objective and capture an image of it seen through a cuvette filled with saline solution. According to this solution, an image is first captured with an optical power of zero and then 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 in which 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 US2007121100 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, a lens, and a mirror inclined at 45°. 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 each lens is designed according to said position. Application WO2019002656 describes a device for measuring the optical power of optical test systems (4). The device includes an assembly that generates an optical object (2), a support (3) for the optical test 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 an eyeglass lens without the need to measure the surface geometry of the crystal. It includes: 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 ray; 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.

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.

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 correcting and compensating for a wide range of these aberrations. There are variable-power lenses based on electrowetting, for example, the opto-fluidic lens, or TOFU lens, from the English 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 can be corrected up to the fourth radial Zernike order. This lens is adjustable by the action of a voltage change. Examples of this type of lenses can be found developed in application EP3123213A1.

Currently known solutions present at least one of the following limitations when determining aberrations or measuring optical characteristics in optical and ophthalmic lenses:

- High influence on the part of the professional handling the device.

- Existing devices have large dimensions

- Low portability

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

- Increasing precision involves high complexity and cost

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

Summary of the invention

The object of the present invention is to provide a solution to the problems that currently exist when 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, both contact lenses and those used in glasses or other optical aberration correction systems. Specifically, the present solution relates to a device for determining aberrations or measuring optical characteristics that comprises a variable focus optical unit such as, for example, a TOFU lens. 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.

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 formed optical axis. The illumination source is configured to illuminate along the optical axis, in the direction of the target system. The target system, for example, a test 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. Additionally, the device comprises a support means for a test lens. Said support means is configured to support an ophthalmic lens, the test lens, in a measuring position on the formed optical axis. A test lens is understood to be the lens whose characteristics are to be determined.

The variable focus optical unit is a variable dioptric power element, which can be either solely spherical or solely astigmatic, or a combination of both characteristics, capable of generating high-order aberrations by electronically controlling 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, where said interface comprises a set of tunable actuation zones. Said tunable assembly 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 controller element configured to modify at least one actuation zone of the interface of the variable focus optical unit. In this way, the curvature modification 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 image of the target system.

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. By adjusting the curvature of the variable-focus optical unit, the image generated in the image capture system's detector plane results in a sharp image and can be used as a reference image. However, when the test 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 it is not necessary to modify the distance between lenses, as is the case with known solutions, a compact device is achieved.

In a second aspect of the invention, the solution relates to a method of 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 image capture system is clearly visible. To achieve 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. Next, the user of the device places a problem lens on the support means configured for this purpose, resulting in a blurred image in the detector plane of the image capture system. To achieve image refocusing, the curvature of the variable focus optical unit is acted upon. The result of modifying the curvature of the interface of the variable focus optical unit is the displacement of the plane where the image of the object system is formed, allowing refocusing of the image on the plane where the detector of the image capture system is located. 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. Finally, once refocusing is complete, the curvature change can be determined to refocus the image, compared to the initially adjusted curvature, and thus, the change in this curvature can be correlated with an optical characteristic of the target lens, for example, the lens's dioptric power.

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 minimal 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.

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

1 Lighting source

2 Object system

3 Condenser lens

4 Test

5 Problem lens

6 Variable focus optical unit

61 Interface

62 Set of action zones

7 Image capture system

8 Focusing lens

9 Detector

10 Optical axis

Brief description of the figures

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

Figure 2 shows a schematic of an embodiment of a variable focus optical unit comprising an interface and a set of actuation zones formed by 32 electrodes.

Figure 3 shows a detailed diagram of the arrangement of an embodiment of a variable focus optical unit between the test and the image.

Figure 4a-4m shows a photograph of an out-of-focus image (left) after insertion of a problem 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, l) -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.

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 test lenses (B) L10, (C) L11, (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.

Detailed description of the invention

In a first aspect of the invention, a device (100) for determining aberrations or measuring an optical characteristic is described.

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). 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.

Thus, in a first embodiment, the illumination source (1) is an illumination source with condensing optics. In this embodiment, the illumination source (1) comprises a condensing 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).

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 axis (10), defocusing the resulting image in the detector plane (9).

For its part, as can be seen in Figure 2, the variable focus optical unit (6) comprises, first of all, a tunable refractive liquid interface (61). That is, the variable focus unit (6) comprises a set of actuation zones (62) configured to modify the curvature of the interface (61). In a particular embodiment, the tuning of the interface is carried out via electrowetting. In this way, the set of actuation zones (62) is tunable via electrowetting. Alternatively, other tuning means can be used such as the mechanical deformation of a membrane (actuated by pressure and/or torsion, among others), dielectric elastomers or even sound or temperature control that are currently under development. In an alternative embodiment, the interface (61) can be tunable by using pressure membranes.

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.

In a particular embodiment, the interface (61) may have a sphero-cylindrical power. Thus, in another 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 in 16 pairs of opposite actuation zones. In this way, 16 meridians can be configured on which the variable focus optical unit (6) acts.

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.

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). In a particular embodiment, the image capture system (7) may be 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.

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.

The inclusion of an external lens, or problem lens (5), in the support medium of a previously focused device (100) can generate a blur of the image in the plane on which the detector (9) of the image capture system (7) is located. Thus, analyzing the dioptric 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 dioptric power different from 0.

As indicated above, the variable focus optical unit (6) has the ability to focus the image by varying the curvature of the interface (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.

In an initial embodiment of the solution, the controller element can be actuated by the user. Alternatively, in another particular embodiment, said controller element can also be actuated automatically.

In order to be able to actuate the controller element automatically, the device (100) may further comprise an image processing system, associated with the capture system (7). Said image processing system may be configured to calculate and send a corresponding signal to the controller 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 the spherical and astigmatic components of the problem lens (5).

In a further embodiment, said image processing system may be a feedback system. According to this feature, the system may perform a series of iterations, sending a signal to the image processing controller element, until a sharp and focused image is obtained. In this way, the user interaction of the device is limited 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. Said numerical analysis is based on metrics such as sharpness, final magnification, blurriness, among others. In turn, the final magnification may 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).

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 processing the image towards the final adjustment measurement.

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.

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.

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:

- 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 sharp image of the object system (2) of the device (100),

- 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).

- refocusing the image obtained on the detector plane (9) by acting on the curvature of the interface (61) of the variable focus optical unit (6);

- determining the change in the curvature of the variable focus optical unit (6); and - correlating the change in the curvature of the variable focus optical unit (6) with an optical characteristic of the problem lens (5).

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, image processing can define an iterative process, automatically feeding back until obtaining a focused image on the detector (9) of the device (100). To do this, a numerical analysis of the image can be performed based on metrics such as sharpness, final magnification, blurriness, among others. 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).

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.

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.

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 great 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.

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

- Lighting source (1) comprising: Thorlabs brand green LED (505nm), and a condenser lens (3): Achromatic doublet with focal length f<’ 1>= 100 mm, Linos brand.

- 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.

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

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

- Image capture system (7) comprising a focusing lens (8), an achromatic doublet with a focal length of 0'& = 40 mm, Edmund Optics model 47665; and a detector (9), IDS UI-3582LE-C (AB00488). It is a CMOS sensor with a resolution of 2560x1920 pixels (4.92 Mpx), 15.2 fps, and a pixel size of 2.2 gm.

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.

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

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.

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, to control the TOFU lens, the image capture system's sensor has been programmed to process the image received. Different combination criteria are applied to the image received by the sensor, based on blurring, edge detection, and magnification. As indicated above, the processing system can be adapted to perform an analysis based on a set of criteria, with sharpness being the most important.

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).

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.

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.

With the previously estimated starting value M, the processing system can perform a sweep of the purely spherical power necessary to refocus the resulting image through the input of the problem lens (5). Specifically, it acts by varying each of the electrodes of the TOFU lens equally, modifying the curvature of the interface. To do this, the value M can be translated into voltage VM by consulting the characterization of the variable focus optical unit (6), and a manual or automatic variation of the voltage is carried out in a range centered on V<m> so that the curvature of the variable focus optical unit is modified as the voltage is varied. The width of said range can be estimated by the eccentricity, such 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 into voltage V and multiplied by a factor of 1.75. In the case of a voltage range less than 0.75 V, a range of 0.75 V is set. In these sweeps, the detector (9) captures the image for each voltage combination 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 sharpness calculation 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, the sharpness of said image is calculated, which translates into 30 sharpness values related to the voltage.

Sharpness will increase to a point of better 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.

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

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° to 180°. One of the orientations is expected to give better image quality (sharpness), and this would select the orientation of the lens astigmatism.

II. Astigmatism scanning: in the orientation chosen in the previous step, 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.

III. It focuses on the calculated value of the eccentricity, for example, ± equivalent to 0.75 D. For several voltage values, the sharpness of the resulting image is calculated and the image voltage with the best sharpness is chosen.

IV. Final spherical adjustment scan: As a final check, a spherical scan is performed again, in which each target area is varied equally; for example, the voltage of each electrode, based on the voltage value obtained in the astigmatism scan step. Once again, the curvature values, or curvature-modifying voltages, that provide the sharpest image among those obtained in the scan are chosen.

The combination of all voltages gives a sharp image in all orientations. Obtaining a sharp image in all directions 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 for 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 principal powers are located).

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.

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 processing the image towards the final adjustment measurement.

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.

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).

Figures 4a-4f and Figures 4h-4m show a photograph of an out-of-focus image (left) after insertion of 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), different from 0.00 D, in the support means of the device (100) produces a certain blurriness. Said blurriness is corrected by adjusting the TOFU lens, which compensates for the action of the problem lens (5), and the final image when the compensation has been carried out with the TOFU lens and therefore the measurement, as a function of the spherical power of the problem lens (5) indicated by the manufacturer.

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 steps of 2 D, 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.

Table 2. Frontal dioptric power results

Additionally, a Zemax simulation was performed on spherocylindrical 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.

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

Table 3 shows the frontal power results for the spherical-cylindrical test lenses: 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 one obtained from the measurement in spherical-cylindrical notation.

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

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

The differences obtained in frontal power averaged 0.022 ± 0.010 D in the Zemax measurements and -0.007 ± 0.018 D in the experimental measurements. The maximum differences were 0.036 D and 0.075 D, for the Zemax and experimental measurements, respectively. Given that 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 expected behavior of the TOFU lens, taking into account the manufacturing tolerances of the TOFU lens.

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.

A second embodiment of the present solution has been carried out with the following components. The experiment has been performed with the following components: Illumination source (S) comprising a Thorlabs green LED (505 nm), and a Linos brand achromatic doublet condenser lens (L1), focal length f'i = 100 mm.

- Object system (2) comprising a Test (4), contact grid of 26 mm diameter.

- Variable focus optical unit (6) comprising a 32-electrode sphero-cylindrical TOFU lens according to the dimensions in Table 5.

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

- Image capture system (7) comprising a focusing lens (8), an achromatic doublet with a focal length of 0'& = 40 mm, Edmund Optics model 47665; and a detector (9), IDS UI-3582LE-C (AB00488). It is a CMOS sensor with a resolution of 2560x1920 pixels (4.92 Mpx), 15.2 fps, and a pixel size of 2.2 pm.

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

In this second example, measurements were taken on nine spherocylindrical 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 test lens, voltages are obtained that recreate a refractive interface that positions 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 test lens to be obtained.

The results are shown in Table 6 and 7.

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

Table 7. Voltage measurement results for each lens.

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

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 (15)

1. - A device for determining aberrations of a lens, where the device (100) is characterized in that it comprises an optical system comprising, located around an optical axis (10); <o>an input illumination source (1) configured to illuminate along an optical axis (10) in the direction of an object system (2), <o>an object system (2) configured to form an image on the optical axis (10); <o>a support means arranged in a measuring position, configured to support a test lens (5) on the optical axis (10) of the optical system, <o>a variable focus optical unit (6) without axial displacement comprising ■ a refractive liquid interface (61), ■ a set of tunable action zones (62) configured to modify the curvature of the interface, and ■ a control element configured to modify at least one actuation zone (62) of the interface (61) of the variable focus optical unit (6); and <o>an image capture system (7), comprising a detector (9) configured to capture the image of the object system (2) formed at the end of the optical axis (10). 2. - The device according to claim 1, wherein the illumination source (1) is an illumination source with condensing 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 interface (61) is an interface with sphero-cylindrical power. 7. - The device according to any one of claims 1 to 6, wherein the set of action zones (62) is tunable via electro-wetting. 8. - The device according to any one of claims 1 to 7, wherein the set of actuation zones (62) comprises at least two pairs of actuation zones (62a, 62b). 9. - The device according to any one of claims 1 to 8, 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). 10. The device according to any one of claims 1 to 9, wherein the image capture system (7) is configured to digitize the image captured by the detector (9). 11. The device according to claim 10, wherein the device (100) further comprises an image processing system. 12. The device according to claim 11, wherein the image processing system is configured to perform a numerical analysis of the focus. 13. The device according to any one of claims 11 to 12, wherein the image processing system emits a drive signal to the controlling element of the variable focus optical unit (6). 14. Method for determining the 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 13, calibrating the variable focus optical unit (6) so that the image formed on the detector (9) of the image capture system (7) is a sharp image 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 is modified; - determine the modification of the curvature of the interface (61); and - correlate the modification of the curvature with an optical characteristic of the problem lens (5). 15. Method according to claim 14, wherein the method comprises automatic refocusing of the image.