ES2627797B1 - OPTICAL ELEMENT FOR THE COMPENSATION OF REGULAR ASTIGMATISM WITH TOLERANCE TO ROTATIONS REGARDING THE AXIS OF EYE ASTIGMATISM AND ASSOCIATED METHOD - Google Patents

Abstract

Optical element for compensation of regular astigmatism with rotation tolerance with respect to the axis of ocular astigmatism and associated method. # The object of the present invention relates to a method of manufacturing an optical element for compensation of regular astigmatism, with total tolerance or partial to rotations of said element with respect to the axis of ocular astigmatism. The method comprises defining the surface of said optical element, so that the error of the ocular wavefront is compensated due to regular astigmatism by means of the wavefront produced by said optical element. Said compensation includes the introduction of high-order aberrations, in terms of Zernike polynomials, in the refractive profile of said optical element, to optimize its visual quality in a range of rotation errors with respect to the axis of astigmatism to compensate. The invention also relates to optical elements such as contact lenses, suitable for regular astigmatism compensation, and manufactured by said method.

Description

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spherical) that is necessary to compensate for the refractive defect and, thus, achieve the correct imaging of distant objects.

Myopia is a refractive defect in which the ocular optical system has more dioptric power than is necessary, so it is compensated with spherical lenses of negative (divergent) power. On the other hand, farsightedness is compensated with spherical lenses of positive (convergent) power, opposite to the power deficit that the ocular optical system suffers. What is involved, in this case, is to compensate for the defect with a refractive profile opposite to the error that the eye has.

Refractive defects that cannot be fully compensated effectively by spherical lenses are usually referred to as astigmatic refractive defects, and were first described by Thomas Young in 1801. Typically, the cause of this type of defect is found in the geometry of the first corneal surface.

An astigmatic refractive defect is said to be cylindrical when it can be satisfactorily compensated by the addition of a cylindrical lens with power in a suitable orientation. When the combination of a spherical and a cylindrical lens is necessary, the sphero-cylindrical astigmatic refractive defect is mentioned.

At present, the combined effect of a cylindrical and a spherical lens is achieved by lenses with toric surfaces. The astigmatic refractive defect that can be adequately compensated with a combination of spherical and cylindrical lenses is called regular astigmatism, or spherical-cylindrical.

Finally, there are also subjects with refractive defects for which there is no spherical-cylindrical compensation that achieves good visual quality, even in the absence of sensory or perceptual pathology. This type of refractive defect has traditionally been known as irregular astigmatism.

Obviating the possibility of adapting rigid contact lenses in the case where regular astigmatism is mostly corneal, the optimal compensation of irregular astigmatisms must be carried out by means of lenses with geometries different from the traditional ones (spherical and toric), being such more demanding lenses in terms of positioning criteria in front of the eye than the spherical lenses

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cylindrical Therefore, it is not usual to find refractive compensation for irregular astigmatisms in the market.

In what can be considered as a great advance towards the understanding and compensation of irregular astigmatisms, an alternative classification of ocular refractive defects has been extended in the field of vision sciences. This classification, instead of being based on the geometry of the lens that is used to compensate them, is based on the analysis of the wavefront aberration presented by each eye in question.

The aberration of the ocular wavefront, called W (p, 0) (expressed in polar coordinates), is the difference between the wavefront produced by the eye after refracting the light and the one it should have to achieve good visual quality In far vision. It is represented as a two-dimensional map that is defined on the pupillary opening and, today, it is possible to measure it objectively with instruments called eye aberrometers.

The eye aberrometers parameterize the wavefront according to its composition as the sum of Zernike polynomials on the pupillary opening. Said Zernike polynomials can be expressed in polar coordinates, Znm (p, 0), where p is the radial coordinate with a variation interval [0,1], and 0 the azimuthal component with a variation interval of [0.2n], and they consist of a radial factor Rnm (p) defined by the following equation:

angular frequency

The polynomials Znm (p, 0), expressed in polar coordinates (p, 0), allow you to write the function of the wavefront of the aberration W (p, 0) as:

Typically, Zernike polynomials are grouped according to the integer to which the radial coordinate of their analytical expression is elevated, so that the

aberration of the ocular wavefront is quantified with a value in microns according to the

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image 1

The lower index (n) denotes the degree of the radial polynomial and the upper index (m) denotes the

image2

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importance of its composition of each of the second, third, fourth, fifth and sixth order groups in the total wavefront aberration. In more detail, the importance of each of the terms that make up each order is quantified by the value of its corresponding coefficient also measured in microns. Figure 1 of this document shows the pyramid corresponding to the Zernike polynomials grouped according to the order and the most conventional name for each polynomial.

In connection with the classical classification of refractive defects such as spherical, sphero-cylindrical (or regular) and irregular, it is generally understood that the coefficients of Zernike polynomials of order 2 (called low order coefficients) determine the type and degree of sphero-cylindrical compensation, while the coefficients of order> 2 (called high order coefficients) determine how irregular the astigmatic refractive defect in question is.

Most astigmatic refractive defects are regular, and are adequately compensated with properly oriented sphero-cylindrical lenses. Similarly to the compensation with spherical lenses, typically an optimal spherical cylindrical compensation should have a refractive profile inverse to the refractive defect that the eye possesses, so that it is compensated and the patient achieves good visual quality. Consequently, each regular astigmatism has a pair of lenses that, properly oriented, manage to provide good quality to the subject who suffers from it.

When the axis of the sphero-cylindrical lens is perfectly parallel to the axis of ocular astigmatism that is to be compensated, the patient achieves good visual quality. However, when it is not possible that the spherical-cylindrical compensation axis remains parallel with the axis of ocular astigmatism, the visual quality decreases and may be unacceptable to the user. A retinal image simulation obtained with sphero-cylindrical compensations with different orientation errors is presented in Figure 2 of this document. In said figure, when the axis of the correction cylinder is 180 °, the quality of the retinal image is maximum for all the ametropias of the figure.

The problem of fitting correctly oriented sphero-cylindrical lenses with respect to the refractive defect of each individual can be reasonably solved for glasses,

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provided that the technology of measurement, marking, blocking and carving of lenses currently exists is used with the appropriate precautions.

However, when sphero-cylindrical compensation is dispensed as a contact lens, ensuring that the axis of the compensating cylinder will be oriented parallel to the axis of ocular astigmatism is much more uncertain, due to factors that destabilize the lens and cause it to lose Its optimal orientation.

Studies indicate that more than 30% of the contact lenses that fit are soft toric contact lenses. This data is very similar to the percentage of prescriptions with an amount equal to or greater than 0.75D of astigmatism, so that optimal visual quality should be guaranteed to these patients. Patient satisfaction with toric contact lens depends on several factors. Comfort, an optimal and stable vision and a good corneal physiology are some of the most important and, for example, the lack of stability in the orientation is usually the main cause of success or failure in the adaptation of contact lenses. This situation of instability is mainly due to the position of the eyelids and the eyelid dynamics. To minimize this problem and ensure optimal and stable vision during transport, contact lenses incorporate different stabilization methods. However, all of them can pose problems to the patient that are, mainly, related to the appearance of discomfort in the use of the lens, and to the increase of complexity in its manufacturing process. Some of these methods are described below.

Use of ballasts prisms: it is one of the most used methods, and includes the use of a lower base prism that makes the contact lens more thick in the lower part than in the upper one. Therefore, the upper eyelid tends to move the lower area down, rotating the contact lens to an unwanted position. Some examples of ballasted prisms are described in US 4573774, US 5125728, US 5020898 and WO 1998045749.

Dynamic stabilization: consists in giving a smaller thickness to the upper and lower area of the lens in relation to its central area. Some of these designs can be seen in US 4095878, US 5650837 and US 8646908. The thickest area in the vertical can also be maintained along the palpebral opening and the thinnest line in the horizontal. This difference in thickness causes that, when the eyelid acts on the

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contact lens, it maintains stability, as in the invention described in US 5100225.

Adaptation to the patient's cornea: In this case, the shape of the cornea of the wearer is taken into account for the design of the optimal base curve that allows stabilization of rotation (see, for example, US 6406145). Sometimes an optimization is also included according to the geometry of the eyelids as in the method described in US 8668331.

Truncated: it involves the removal of a part of the contact lens, usually between 1 and 1.5 mm from the lower area so that the lens rests on the lower eyelid.

Alternatively, contact lenses have also been designed with other stabilization methods that employ channels, ridges or small holes as a stabilization method, such as those described in US 4211476, US 6626534 and US 5009497. Despite the variety of stabilization methods It is not usual to find that a contact lens only uses one design. Most commonly, a combination of stabilization methods is used, as described in US 8690320 and US 7628485.

The techniques described above assume valid approximations for the stabilization of the lens position in the user's eye. However, these techniques are not without problems that mainly affect the discomfort in their use and, sometimes, the appearance of irritation due to the interaction of said lenses with the patient's eyelid. Also, increases in the thickness of the lens as a result of introducing the different stabilization elements, imply a lower transmission of oxygen in that area of the cornea through the material, and this can also create discomfort to the patient who uses it.

A possible sub-optimal solution, to compensate for astigmatism and avoid stability problems, is to employ a rotation-tolerant optical element, such as a lens with only spherical power, with the intermediate value between the maximum and minimum powers of the Optimum sphero-cylindrical lenses, using what is called the spherical equivalent (S + C / 2). Compensation for regular astigmatism with a spherical lens is tolerant of rotation, although visual quality may be insufficient

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for certain amounts of astigmatism, as seen in Figure 3 of this document.

Today, there is a wide variety of soft monofocal, bifocal and multifocal contact lenses on the market, both to correct spherical errors and astigmatisms. However, patients with high astigmatism do not fall within the range of available cylindrical powers as molded contact lenses have a limited range of powers. In these cases, they are forced to acquire personalized contact lenses, which implies a considerable increase in price, as a result of the greater complexity of the lenses. Alternatively, there are also lenses available for immediate sale, such as daily, biweekly or monthly replacement contact lenses. However, patients with high astigmatism, for whom the tolerance to the rotation of the cylinder axis is very small, have a very limited range to choose between such lenses.

As a consequence of the limitations and problems posed by the known solutions described above, the need arises to obtain optical elements, preferably contact lenses, that correct the defects of regular astigmatism of the patient during use, stably before rotations in relation to the axis of astigmatism, that are not uncomfortable or irritating to the user, and that can be manufactured using industry standard techniques belonging to this field. The present invention is oriented to satisfy said need.

BRIEF DESCRIPTION OF THE INVENTION

In view of what is described in previous paragraphs, an object of the present invention is, therefore, to obtain methods of manufacturing optical elements for the compensation of regular astigmatism, with total or partial tolerance to rotations or changes in position of said element. regarding the axis of ocular astigmatism.

Said object is preferably performed by obtaining optical elements for astigmatism compensation whose surface comprises a wavefront that is described by a function F (r, 0) with triaxial symmetry such that, expressed in polar coordinates, F ( r, 0) = F (r, (0 + n2n3)) for integer n, where r is the radial coordinate with respect to the center of the surface of the optical element, and 0 is the polar angular coordinate on said surface.

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In a preferred embodiment of the invention, the wavefront is described by a function F (r, 0) proportional to the product R (r) -G (0), expressed in polar coordinates, where R (r) is a function with Radial symmetry and G (0) is a function with angular geometry defined as G (0) = G (0 + n-2-n3).

In another preferred embodiment of the invention, the function R (r) is described as a sum of functions R (r) = IRnrn, where n is between 1 and infinity and Rn is a constant coefficient.

In another preferred embodiment of the invention, the wavefront is defined by the function F (r, 0) = CT (R (r) G (0)), where CT is a constant between 0.15 and 2 microns.

In another preferred embodiment of the invention, the function of the wavefront F (r, 0) is combined with a spherical compensation phase, defined by the function FD (r, 0) = D (2RD (r) -1), where RD (r) = r2, and the constant D corresponds to the spherical equivalent (S + C / 2) of the sphero-cylindrical ametropia to compensate, expressed in microns.

In another preferred embodiment of the invention, the function of the wavefront F (r, 0) is combined with a regular astigmatic compensation phase, defined by the function Fa (r, 0) = A-RA (r) -cos2 ( 0 + AA), where RA (r) = r2 and where Aa is between 0 and n / 2 radians. More preferably, A is a constant between 0 and 4 microns.

In another preferred embodiment of the invention, the optical element is a contact lens.

For the realization of the optical elements described by the present invention, a method is carried out which comprises the definition of the surface of said optical elements (mainly, their anterior surface with respect to the tracing of the incident ray in the eye), so that the error of the ocular wavefront is compensated due to regular astigmatism by the wavefront produced by said optical element.

Advantageously, said compensation includes the introduction of high-order aberrations, in terms of Zernike polynomials, in the refractive profile of said optical element, to optimize the visual quality thereof in a range of rotation errors with respect to the axis of astigmatism to compensate . More preferably, the

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Additional introduction of low-order aberrations in the refractive profile of the optical element in combination with high-order aberrations, to compensate for the error in the eye wave front.

For the optimization of the visual quality, an iterative algorithm of adjustment of the introduced aberrations is preferably used, until reaching a desired value of said visual quality for the range of rotation errors with respect to the axis of astigmatism. Examples of such algorithms are, for example, Levenberg-Marquardt adjustment procedures, or simulated annealing algorithms.

For the definition of the surface of the optical element of the invention, said optical element comprises its parameterization based on Zernike, B-Splines or Fourier harmonics polynomials, by means of a composition of one or more two-dimensional regions.

Likewise, the visual quality is calculated, preferably, by the wavefront calculated by actual ray tracing across the surface of the optical element, for the range of rotation errors with respect to the axis of astigmatism to be compensated. More preferably, the method of the invention comprises the calculation of the subjective refraction of the eye to be compensated to obtain the sphere, cylinder and axis necessary to achieve the desired visual quality, and the calculation of the wavefront to be presented by the optical element for said prescription.

In another preferred embodiment of the invention, it is also possible to provide the optical element with a partial tolerance calculated as a function of the value of the residual cylindrical component that occurs when the compensation with respect to ametropia is rotated.

In another preferred embodiment of the invention where the optical element is a contact lens, it is also possible to incorporate one or more stabilization means of said lens, wherein said means comprise the use of ballasts, dynamic stabilization, surface adaptation internal lens to the patient's cornea and / or truncated.

The present invention thus comprises a set of techniques for the design of contact lenses, capable of compensating sphero-cylindrical ametropias with a high tolerance to an error in their rotational orientation, as far as visual quality is concerned. Dispose of

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An element that adequately compensates for regular astigmatism, without the need to maintain a specific orientation with respect to the ocular axis, can mean a remarkable advance in the technical field of the invention, since:

- It involves more comfortable contact lenses for the user, since it is not necessary to thicken the peripheral areas of the same asymmetrically, to stabilize their orientation.

- High astigmatisms, whose compensation with a sphero-cylindrical lens is potentially intolerant of rotations, can achieve compensation that provides a more stable visual quality, despite the turns of the lenses during flickering or during lens insertion.

- It allows to benefit from the use of daily disposable lenses to a greater amount of astigmatic population, since a single lens design can be valid for a wide range of astigmatism axes. As mentioned above, single-use contact lenses are only available for a very limited range of axes in each cylindrical power.

- Potentially, contact lenses for compensation of presbyopia by simultaneous vision could also benefit from the method of the invention, adding astigmatism compensators tolerant to the orientation of the cylinder in its refractive profile. Finding a compensation for regular astigmatism for which it is not necessary for the lens to be oriented implies the reduction of a parameter to consider when presenting a range of lens manufacturing.

DESCRIPTION OF THE DRAWINGS

To complete the description of the invention and in order to help a better understanding of its technical characteristics, the present document is accompanied by a set of figures where, for illustrative and non-limiting purposes, the following is represented:

Figure 1 shows the pyramid corresponding to the Zernike polynomials, grouped according to the order and the most conventional name for each polynomial.

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Figure 2 shows a retinal image simulation obtained with sphere-cylindrical compensations with different orientation errors, according to a known embodiment belonging to the state of the art.

Figure 3 shows a compensation of a regular astigmatism with a spherical lens would be tolerant of rotation, according to a known embodiment belonging to the state of the art.

Figure 4 shows a schematic of an optical element according to a preferred embodiment of the present invention, comprising a surface configured to produce a wavefront with triaxic symmetry (Figure 4a) and a schematic representation of an astigmatic eye (Figure 4b).

Figure 5 shows schematically, in three stages (Figures 5a-5c) the result of superimposing and rotating the triaxic symmetry wavefront produced by the optical element of the invention (horizontal stripes) on an astigmatic eye. When rotating the triax wave front over the eye, there is a partial compensation of astigmatism (overlap zone).

Figure 6 shows retinal images of a Snellen visual acuity optotype equal to 1, observed through a contact lens made according to the method of the invention (left), placed with the corrective axis parallel to the axis of astigmatism (0 ° ) and rotated + 20 ° and -20 ° over the eye of a patient P1 (upper row) and over the eye of the patient P2 (lower row). Retinal images are shown on the right with a contact lens of traditional design without high-order aberration (indicated as "without HOA"), with its correct spherical cylindrical compensation and rotated 20 ° on the same ametropic eyes.

Figure 7 shows retinal images of a Snellen visual acuity optotype equal to 1, observed through the rotated contact lens 0 °, 10 °, 30 ° and 90 ° over the eye of a P1 patient (upper row) and over the eye of a P2 patient (lower row).

Figure 8 shows retinal images of a Snellen visual acuity optotype equal to 1, observed through the traditional contact lens (spherical cylindrical correction only) rotated 0 °, 10 °, 30 ° and 90 ° over the eye of a patient P1 (upper row) and over the eye of a patient P2 (lower row).

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DETAILED DESCRIPTION OF THE INVENTION

As described in preceding paragraphs, the present invention relates to a method of design and manufacture of optical elements (for example, contact lenses) for the compensation of regular astigmatism whose optical zone is tolerant, in its positioning in front of the optical system ocular, to rotations and offsets of its position against the axis of astigmatism of the eye. The invention also relates to the optical elements obtained by the application of said method.

As mentioned in the background description of the invention, existing contact lenses seek to compensate for astigmatism by means of optical zones with refractive profile that, with the proper orientation, conjugate the ocular refractive error. However, the present invention relates, as an improvement to known technologies, to contact lenses with an optical zone specially designed to compensate for astigmatism, and which are advantageously also invariant to the rotation / decentration of said lenses in the eye. In this type of compensation, it is not intended, therefore, the conjugation of the ocular wavefront error with the wavefront produced by the element to compensate, but rather a sufficient compensation of regular astigmatism by means of optimal amounts of high-order aberrations in the profile refractive (n> 2, if described in terms of Zernike polynomials). In order for the raised element to function properly, these additional amounts of high-order aberrations must be able (if necessary, in combination with the appropriate terms of order 2) to maintain said partial compensation against rotations of the contact lens in the optical zone in the They are registered. In this sense, due to their geometric peculiarities, the use of said high-order aberrations constitutes an essential element of the invention since, by means of its adjustment in the definition of the surface of the optical element, it is possible to obtain the properties of triactic symmetry mentioned, thanks to which the regular astigmatism compensation is obtained for any orientation of the optical element in relation to the astigmatism axis.

The optical element referred to in the present invention is characterized by comprising a surface that produces a wavefront that is described by a function F (r, 0) with triaxic symmetry (Figure 4 of this document), so that F ( r, 0) = F (r, 0 + n2n3), where n is an integer. Said wavefront F (r, 0) is defined by the expression F (r, 0) = R (r) G (0) as the product of a radial function R (r) = Irn with n = 1 ... .m, being m

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an integer, and another angular function G (9) = G (0 + n-2 ^ n3). Additionally, F (r, 0) can comprise a multiplicative constant CT, adopting the form F (r, 9) = CTR (r) G (9). The CT value is preferably 0.15-2 microns (for a pupil radius r = 3mm, normalized to the unit circle).

Optionally, the optical element of the invention may be combined with a spherical compensation phase, defined by the function FD (r, 0) = D (2RD (r) -1), where RD (r) = r2, and the constant D corresponds to the spherical equivalent (S + C / 2) of the spherical cylindrical ametropia to be compensated; and / or with a regular astigmatic compensation phase, so that Fa (r, 9) = AR (r) cos2 (9 + AA), where R (r) = r2 and where Aa is a phase between 0-n / 2 radians. The constant A is between 0-4 microns (for a pupil radius r = 3mm, normalized to the unit circle).

The combination of a function F (r, 9) with the appropriate CT value with a regular astigmatic compensation phase Fa (r, 9), gives rise to an optical element that, when rotated in front of an astigmatic eye, compensates for the ametropia of partial or total way, whatever the orientation of that element.

Figure 5 shows schematically what happens when superimposing and rotating the triactic symmetry wavefront produced by the element of the invention (horizontal stripes) over an astigmatic eye (vertical stripes). When rotating the triax wave front over the eye, there is a partial compensation of astigmatism (overlap zone). The area corresponding to this partial compensation remains constant during the rotation of the triactic wavefront. The areas that do not have compensation cause the rays that pass through the system to deviate, creating a halo that reduces the contrast, but does not reduce the visual acuity. This characteristic gives the element of the invention the ability to tolerate rotation with respect to the axis of astigmatism.

To obtain the specific geometry of the optical elements according to the invention, an optimization process of the optical zone is performed, using as an optimization element the visual quality obtained by the optical element, for a range of rotation errors with respect to the axis of astigmatism To compensate. Said process preferably comprises first measuring subjective refraction and aberration of the patient's wavefront. Subsequently, the visual tolerance to the rotation of your

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optical sphere-cylindrical compensation, by numerical simulation and / or by subjective estimation (by test lens, visual simulation, etc.).

With this information, the CT and A values appropriate to the subjective refraction and the wavefront aberration of the patient are calculated, as well as the degree of visual tolerance to the rotation of their spherical-cylindrical optical compensation. Such calculations can be performed, for example, by computer simulation or by carving elements that provide different wave fronts, performing experimental tests on the patient.

After obtaining the values of CT and A, the corresponding contact lens that produces the final wavefront is manufactured. In the case of the design that provides partial tolerance to rotation, the most appropriate stabilization method will be included. Finally, the contact lens is adapted and tested in its use by the patient.

- Examples of design and manufacture of the optical elements according to the method of the invention:

Design example 1: The appropriate value of CT and A can be obtained through the use of analytical equations, depending on the type of tolerance required for the optical element. For a configuration in which it is desired to obtain a total rotation tolerance, the value of CT is calculated based on the value of the cylindrical component of the refraction (C) by means of a second degree polynomial function Tf (C) with AT coefficients , BT and CT (Table 1 of this document).

 Tolerance (Tol)

 At Bt Ct

 Universal

 0.085 0.104 0.645

Table 1

In this case, the regular astigmatic phase Fa (r, 0) that would be added to the function F (r, 0) would be zero (A = 0) and the spherical phase FD (r, 0) corresponds to a phase of (S + C / 2) diopters.

In the case that the element to be configured presents a design with a partial tolerance (Tol), the CT value that will be added to the design of the optical element is calculated on the one hand, of the value of the residual cylindrical component (CR ) That

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it produces when rotating the compensation with respect to the ametropia a certain number of degrees (Tol) and, on the other hand, of the own tolerance value (Tol) that it is wanted to provide.

In this case, the regular astigmatic phase Fa (r, 0) that would be added to the function F (r, 0) would be the one corresponding to the amount of astigmatic refraction to be compensated and the spherical phase FD (r, 0) corresponds with a phase of (S + C / 2) diopters.

The partial compensation design that can incorporate, according to the tolerance that is desired to provide to the element, any of the existing stabilization methods in the market.

Design example 2: It is also possible to determine the value of the desired CT and A coefficients by means of a wavefront simulation system, with the aim of checking different designs to the subject until the astigmatic ametropia compensation present is tolerant to partial and / or total rotation.

Design example 3: On the other hand, carving elements that provide different wave fronts to perform experimental tests on the patient would also be a valid method to obtain the CT and A coefficients.

For the design of the optical zone of the contact lens of the invention, optimization is preferably carried out only on the anterior surface of the optical zone, since that of the posterior face is usually chosen with a determined geometry independently of the refractive error, to facilitate comfort in the lens bearing by the user.

For the optimization of the front face of the lens, its surface can be parameterized as the composition of a series of two-dimensional functions, optimal for manufacturing with existing instruments in the industry for carving contact lenses (Zernike polynomials, B-splines, Fourier harmonics, etc.). The surface may be defined by a single zone, or as a set of multiple bordering zones.

The visual quality is preferably calculated by the wavefront calculated by actual ray tracing across the surface, for each of the orientation errors. As the visual quality metrics that have best been demonstrated

correlate empirically with visual quality depend nonlinearly with the

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Wavefront, the technique to choose for optimization can be, for example, a valid algorithm for this type of parametric dependence (for example, Levenberg-Marquardt, "Simulated Annealing", or a similar one among those known in the state of The technique).

In a preferred embodiment of the invention, optimization is carried out directly on the wavefront error that occurs when compensating the astigmatism with the element to be optimized. In this way, once the wavefront that the compensating element must have to be rotatable tolerant is obtained, an optimization of the anterior surface of the contact lens is carried out by means of real ray tracing, so that the optical zone presents said refraction when a flat wave front hits it.

- Examples of application of the contact lenses of the invention:

Application example 1: Myopic patient with different astigmatisms and compensation tolerant to a rotation range of ± 20 °.

The case of a myopic patient (P1) with a refraction (Rx1) -1.00DE -0.75DC x 70 °, and a myopic patient (P2) with a refraction (Rx2) -1.00DE -3.75DC is analyzed. x 70 °, both with a pupil radius (R) of 3 mm. They are prescribed a contact lens made according to the method of the invention, which allows them to see a line of visual acuity of Snellen equal to 1, maintaining good visual quality for a rotation range with respect to the axis of astigmatism of ± 20 °.

For this, a measurement of the subjective refraction of the patient is made to obtain the sphere, cylinder and axis that it needs to achieve the best possible visual acuity.

One of the design methods of the element would be by calculating the functions F (r, 0), FD (r, 0) and Fa (r, 0) that the optical element must present for this prescription. For this example, we use a wavefront F (r, 0) defined by the product of a radial part R (r) = r3, another angular part G (0) = cos (30 + A), where A has a value which optimizes peripheral thicknesses, and a CT value> 0.2 microns for P1 and a CT value> 0.75 microns for P2, both for a pupil radius (R) of 3 mm. For this example, element A will be the value in microns of the total compensation and the spherical phase, FD (r, 0), corresponds

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with a phase of -1.38 D for P1 and -2.88 D for P2. Next, the CT value that provides the desired tolerance at the rotation range ± 20 ° is calculated.

Once the parameterization of the ocular element is obtained, the optical element is manufactured as a contact lens, so that its refractive profile introduces the wavefront calculated in the previous step, for each of the patients with the calculated coefficients . For the design of the optical zone of the contact lens, the optimization is preferably performed only on the anterior surface of the optical zone, since that of the posterior face is usually chosen with a geometry determined independently of the refractive error, to facilitate the comfort in the bearing of the lens by the user.

Taking into account the calculated contact lens parameters and through the use of commercial software, the geometry of the front surface of the contact lens is defined, also setting its posterior radius (rp = 8.3 mm), the index of material refraction (n = 1.42), the diameter of the optical zone (0zo = 6 mm) and its minimum thickness (tm = 0.1 mm)

Finally, the contact lens is adapted to the patients in question. The adaptation is carried out through the typical contact lens adaptation protocols (placement and removal review, etc.).

Figure 6 of this document shows the retinal images of an optotype with a = 5 arc minutes, corresponding to a Snellen visual acuity equal to 1, observed through the contact lens placed with the corrective axis parallel to the axis of astigmatism ( 0 °) and rotated + 20 ° and -20 ° over the patient's eye P1 (upper row) and over the patient's eye P2 (lower row). In addition, to the right of said Figure 6 the retinal images for the same eye are shown, with a contact lens of traditional design with its correct spherical cylindrical compensation and rotated 20 °.

As can be seen, the method of the present invention is capable of providing lens designs with a very satisfactory quality of the retinal image within the tolerance range described.

Application example 2: Myopic patients with different astigmatisms and invariant rotation compensation.

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The case of a myopic patient (P1) with a refraction (Rx1) -1.00DE -0.75DC x 70 °, and a myopic patient (P2) with a refraction (Rx2) -1.00DE -3.75DC is analyzed. x 70 °, both with a pupil radius (R) of 3 mm. They are prescribed a contact lens made by the method object of the invention, which allows them to see a Snellen AV line equal to 1, regardless of the position of the element with respect to the axis of astigmatism.

For this, a measurement of the subjective refraction of the patient is made to obtain the sphere, cylinder and axis that it needs to achieve the best possible visual acuity. One of the design methods of the element would be by calculating the functions F (r, 0), FD (r, 0) and Fa (r, 0) that the optical element must present for this prescription. For this example, we use a wavefront F (r, 0) defined by the product of a radial part R (r) = r3, another angular part G (0) = cos (30 + A), where A has a value which optimizes peripheral thicknesses, and a CT value that provides the characteristic of total tolerance, regardless of the position of the element with respect to the axis of astigmatism. For P1 the value is CT> 0.3 microns and for P2 the value will be CT> 1 microns for a pupil radius (R) of 3 mm. For this example, Fa (r, 0) = 0 (A = 0) and the spherical phase, FD (r, 0), corresponds to a phase of -1.38 D for P1 and -2.88 D for P2.

Once the parameterization of the ocular element is obtained, the optical element is manufactured as a contact lens, so that its refractive profile introduces the wavefront calculated in the previous step.

For the design of the optical zone of the contact lens, optimization is preferably carried out only on the anterior surface of the optical zone, since that of the posterior face is usually chosen with a geometry determined independently of the refractive error. This facilitates comfort in the carrying of the lens by the user.

Taking into account the calculated contact lens parameters and through the use of commercial software, the geometry of the front surface of the contact lens is defined, also setting its posterior radius (rp = 8.3 mm), the index of material refraction (n = 1.42), the diameter of the optical zone (0zo = 6 mm) and its minimum thickness (tm = 0.1 mm)

Finally, the contact lens is adapted to the patients in question, using the typical contact lens adaptation protocols (placement and removal review, etc.).

5 Figure 7 of this document shows the retinal images of an optotype with a = 5 arc minutes, corresponding to a visual acuity of Snellen equal to 1, observed through the contact lens obtained according to the method of the invention, rotated a series of different degrees (0 °, 10 °, 30 ° and 90 °) on the eye of patient P1 (upper row) and on the eye of patient P2 (lower row). Figure 8, for its part, shows 10 retinal images for the same eye, with a contact lens of traditional design with its correct spherical cylindrical compensation also rotated the same degrees as in Figure 7.

As can be seen, the method of the present invention is capable of providing 15 lens designs with a very satisfactory quality of the retinal image for any tolerance angle.

Claims (13)

5 10 fifteen twenty 25 30 35 1. Optical element for the compensation of regular astigmatism with rotation tolerance with respect to the axis of ocular astigmatism, characterized in that its surface comprises a wavefront that is described by a function F (r, 0) with triaxic symmetry such that, expressed in polar coordinates, F (r, 0) = F (r, (0 + n-2-n3)) for integer n, where r is a radial coordinate with respect to the center of the surface of the optical element, and 0 is the polar angular coordinate on said surface. 2. - Optical element according to the preceding claim, wherein the wavefront is described by a function F (r, 0) proportional to the product R (r) G (0), expressed in polar coordinates, where R (r) is a function with radial symmetry and G (0) is a function with angular geometry defined as G (0) = G (0 + n2n3). 3. - Optical element according to any of the preceding claims, wherein R (r) is described as a sum of functions R (r) = IRNrN, where N is between 1 and infinity and RN is a constant coefficient. 4. - Optical element according to any of the preceding claims, wherein the wavefront is defined by the function F (r, 0) = CT (R (r) G (0)), wherein CT is a constant between 0, 15-2 microns 5. - Optical element according to any of the preceding claims, wherein the function of the wavefront F (r, 0) is combined with a spherical compensation phase, defined by the function FD (r, 0) = D (2RD (r ) -1), where RD (r) = r2, D is a constant equal to the value (S + C / 2) corresponding to the sphero-cylindrical ametropia to compensate, and / or a regular astigmatic compensation phase defined by the function Fa (r, 0) = A-RA (r) -cos2 (0 + AA), where RA (r) = r2 and where Aa is between 0 and n / 2 radians. 6. - Optical element according to the preceding claim, wherein A is a constant between 0-4 microns. 7. - Optical element according to any of the preceding claims, wherein said element is a contact lens. 5 10 fifteen twenty 25 30 35 8. - Method of manufacturing an optical element for the compensation of regular astigmatism according to any of the preceding claims, with total or partial tolerance to rotations of said element with respect to the axis of ocular astigmatism; which comprises defining the surface of said optical element, so that the error of the ocular wavefront is compensated due to regular astigmatism by the wavefront produced by said optical element; and the method being characterized in that said compensation comprises the introduction of high-order aberrations, in terms of Zernike polynomials, in the refractive profile of said optical element, to optimize the visual quality thereof in a range of rotation errors with respect to the axis of astigmatism to compensate; and because the surface in the optical element obtained by said compensation comprises a wavefront described by a function F (r, 0) with triaxial symmetry such that, expressed in polar coordinates, F (r, 0) = F (r , (0 + n2n3)) for n integer, where r is a radial coordinate with respect to the center of the surface of the optical element, and 0 is the polar angular coordinate on said surface. 9. - Method according to the preceding claim, comprising the additional introduction of low order aberrations in the refractive profile of the optical element in combination with high order aberrations, to compensate for the error in the eye wave front. 10. - Method according to any of claims 8-9, wherein the visual quality is calculated by the wavefront calculated by actual ray tracing across the surface of the optical element, for the range of rotation errors relative to the axis of astigmatism to compensate. 11. - Method according to the preceding claim, comprising the calculation of the subjective refraction of the eye to be compensated to obtain the sphere, cylinder and axis necessary to achieve the desired visual quality, and the calculation of the wavefront to be presented by the optical element for said prescription. 12. - Method according to any of claims 8-11, wherein the optical element is provided with a partial tolerance calculated as a function of the value of the residual cylindrical component that occurs when the compensation with respect to the ametropia is rotated. 13. Method according to any of claims 8-12, wherein the optical element is a contact lens; and wherein said method comprises the incorporation of one or more lens stabilization means, wherein said means comprise the use of ballasts, dynamic stabilization, adaptation of the internal surface 5 of the lens to the patient's cornea and / or truncated .