ES2655268A1 - METHOD AND DEVICE FOR DETERMINING THE SUBJECTIVE SUBJECTIVE EYE REFRACING AUTOMATICALLY (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Method and device for determining the subjective ocular refraction in an automated way, characterized in that the method comprises a previous stage in which an ocular refraction is performed at the beginning and a second stage where ocular refractions are calculated according to range values (R <sub > S , RC , R{al }) and step (PS , PCand P{al }), each ocular refraction is transformed to a power vector with values of sphere (S), power (C) and axis (α) that are transformed to a spherical equivalent (M) and crossed cylinders of Jackson (J0and J45), a metric is calculated for each refraction, the eye refractions are ordered according to this metric, the ocular refractions are shown to the patient until obtaining a final ocular refraction with final values of sphere (S), power (C) and axis (α).

Description

DESCRIPTION

METHOD AND DEVICE FOR DETERMINING THE OCULAR SUBJECTIVE REFRACTION AUTOMATICALLY

 5

Technical sector

The present invention relates to a method and a device for measuring the subjective ocular refraction of a patient. The method consists of a predefined spherical cylindrical lens exchange algorithm that allows to determine the optimal values of 10 power of the S sphere, power of the C cylinder and orientation of the axis of the α cylinder of the lenses that provide the best visual perception for each patient, improving the measurement time with respect to conventional ocular subjective refraction methods, and minimizing the subjectivity introduced by the patient and the examiner. The device that employs the method of the invention belongs to the family of stereoscopic systems of virtual reality and instruments called automated phoropters, and must be able to exchange a set of sphero-cylindrical lenses synchronously with the visual optotypes presented at patient being examined and with a control mechanism that allows the patient to enter information to the device.

 twenty

State of the art

The most recent data from the World Health Organization estimate that refractive error (myopia, farsightedness and / or astigmatism) is the major cause of visual dysfunction, affecting 43% of the general population. It can be concluded that the measure of refractive error belongs to a field of global interest.

The ocular refraction, that is the values of sphere S, cylinder C and axis α of the optimal lenses for the patient, can be obtained objectively or subjectively. On the one hand, objective measures of ocular refraction can now be obtained quickly by means of, for example, autorefractometers or wavefront sensors. These measures are currently used as a starting point for subjective refraction. Although there are several studies that report that most of these devices are accurate and agree with subjective refraction, they are not used directly to prescribe optical corrections given that the patient's satisfaction with this correction as well as their visual acuity with it.

Correction are not enough. The main reason why objective refractive measures are limited is the lack of psychophysical response of the patient.

On the other hand, subjective refraction is considered the reference method for determining ocular refraction. This method is traditionally based on comparing different combinations of sphero-cylindrical lenses, using visual acuity changes as a criterion to reach the combination of S-sphere, C-cylinder and α-axis that results in maximum visual acuity. Commonly, the mechanism for exchanging lenses in subjective refraction is done through the use of phoropters and / or test lenses. Unlike the objective refraction, the subjective refraction is based fundamentally on the psychophysical response of the patient and on the examiner's abilities, giving the subjective refraction a repetitiveness worse than that of the objective methods and a significantly longer measurement time. It should be noted that there is no standardized and unique protocol for the determination of subjective refraction, the most widespread consists of the following steps:

1. Obtain an initial refraction, that is to say initial values of S sphere, C cylinder and α axis, by means of an autorefractometer, wavefront sensor, retinoscopy or even by prior prescription of the patient.

2. Occlusion of one eye of the patient and myopia of the other eye on its initial refraction 20 (for example, a +2.00 D positive spherical lens can be added to its initial refraction).

3. Reduction of the positive lens in steps of 0.25 D until obtaining a visual acuity of 0.8 (in decimal scale) or up to 0.00 D of addition.

4. Estimation of the axis orientation of the α-cylinder through the use of Jackson 25 cross cylinders (JO J45)

5. Estimation of the power of cylinder C through the use of Jackson's crossed cylinders (JO J45)

6. Refinement of the power of the S sphere (adjust the value of the S sphere to maximum visual acuity). 30

7. Repeat the process for the occluded eye.

8. Match the accommodative states of both eyes by using a vertical prism that dissociates binocular vision.

9. Refine the S sphere binocularly.

 35

Note that in each of these steps for the determination of subjective refraction, the patient must respond to the task of discerning different optotypes (usually they are letters or numbers of a specific size). That is to say, in all the steps the psychophysical response of the patient is obtained.

 5

To date, there are very precise objective eye refraction systems but unable to provide the patient with an optical prescription as satisfactory as subjective refraction, and even, they are unable in certain circumstances to execute correctly. In turn, subjective refraction lacks the precision of objective methods, they are more laborious, require a much longer duration and are dependent on the skills between examiners. A good system of ocular refraction should be able to obtain the benefits that come from objective and subjective methods, that is, it should be fast and accurate, it should agree with the reference method (subjective refraction) and should include the patient's psycho-physical response. as well as minimizing the impact of the examiner.

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There are several drawbacks associated with the methods of objective refraction. Among the most notable are the lack of psychophysical response by the patient, this leads to objective refractions that do not allow the patient to obtain optimal satisfaction and / or visual acuity to their subjective refraction. Another drawback of these methods is their high sensitivity to eye diseases such as cataracts or small pupils, in which cases the objective measurement can hardly be performed reliably. Finally, objective methods tend to myopic overcorrection (known as 'instrumental myopia' or 'instrumental accommodation') given their lack of psychophysical response by the patient as well as the fact of being embedded in optical instruments with a relatively visual field reduced and with simple visual stimuli and without depth clues. This myopic overcorrection is also associated with the inability to detect refractive dysfunctions known as latent farsightedness and pseudo-myopia.

The main disadvantages of subjective refraction are its reduced accuracy, that is, the low repeatability and reproducibility associated with the subjectivity of the method (depends on the patient and the examiner), the lack of standardization of the method, as well as the measurement time , while the objective methods allow measurements of the order of a few seconds, the subjective refraction is in the order of 15 to 30 minutes per patient. This time can lead to a greater imprecision in young patients, with little attention span, or with limited communication skills. 35

Object of the invention

According to the invention, a method of subjective ocular refraction is used to determine the optimal values of sphere (S), cylinder (C) and axis (α) of the sphero-cylindrical lenses that provide the best visual perception for each patient. 5

The method of the invention comprises at least:

 a previous stage where an ocular start refraction is obtained according to the start values of sphere (S), power (C) and axis (α); 10

 a first stage where the size of an optotype is determined according to the best monocular visual acuity of a patient for the values of onset of sphere (S), power (C) and axis (α); Preferably, the best visual acuity is performed by means of a psychophysical method of forced choice of four alternatives. But any other psychophysical method could be used.

 a second stage where:

or values of range of sphere RS, of cylinder RC, and of axis Rα, and values of passage of sphere PS, of cylinder PC and of axis Pα are predetermined;

or a set of ocular (ref) refractions within the range values (RS, RC, Rα and with the step values (PS, PC and Pα) are calculated;

or each ocular refraction is transformed to a power vector with values of sphere (S), power (C) and axis (α), said values being transformed to a spherical equivalent (M) and Jackson's crossed cylinders (J0 and J45) according to the following equations:

       [one]

      [2]

      [3] 30

or a metric is calculated for each ocular refraction;

or the ocular refractions transformed to power vectors are ordered according to the

previously calculated metrics;

or the patient is shown ocular refractions with the optotype size determined in the first stage until a final ocular refraction of the second stage is obtained with final values of sphere (S), power (C) and axis (α). 5

Preferably the metric used to order ocular refractions is Euclidean distance (ED), such that:

or a Euclidean distance (ED) is calculated for each ocular refraction according to the following equation:

 . [4]

or the ocular refractions transformed to power vectors 15 are ordered in ascending order according to the Euclidean distance calculated previously;

or the patient is shown ocular refractions with the optotype size determined in the first stage until the final ocular refraction of the second stage is obtained with final values of sphere (S), power (C) and axis (α). twenty

The number of eye refractions is calculated according to the following equation:

   [5]

 25

where RS, RC, Rα are the range values and PS, PC, and Pα are the step values, and

where rounding () is a function that rounds the argument to the nearest integer.

The ocular refractions are shown to the patient consecutively in pairs, the patient having to select a refraction of each pair, where the refractions of the first pair correspond to the refractions for imin = 1 and imax = Nref, while the following pairs of refractions correspond to the refractions for imin = rounding ((Nref + 1) / 2) and imax = Nref, or imin = 1 and imax = rounding ((Nref + 1) / 2). This algorithm of approximation to the correct result of subjective refraction is not limiting, being able to

use other root search algorithms such as the Brent, Newton, secant, interpolation, polynomial, etc. algorithm.

The method can be applied binocularly, for this the previous, first and second stages are applied on both eyes of the patient, the method further comprising in this case a third, and fourth stages. Thus, in the third stage it is checked whether there is anisometropia, both in sphere (S) and in cylinder (C), for this:

or a maximum inter-eye sphere error (EIOS) and a maximum inter-eye cylinder error (EIOC) are preset; 10

or second ocular refractions are calculated between the refraction of the right eye and the refraction of the left eye obtained in the second stage using the ball pitch (PS) and cylinder (PC) values defined in the second stage; fifteen

or each second ocular refraction is transformed to a power vector and a metric is calculated, preferably its Euclidean distance (ED) with respect to a reference refraction selected from one of the second ocular refractions; twenty

or at least three pairs of the second ocular refractions transformed to power vectors are selected and compared with the second ocular refractions to reduce inter-eye error (EIOS, EIOC), obtaining an ocular refraction for each eye with sphere values (S), power (C) and axis (α). 25

In the fourth stage the size of an optotype is determined according to the best monocular visual acuity of a patient for the values of sphere (S), power (C) and axis (α) of the ocular refractions for each eye obtained in the third stage Preferably, the best visual acuity is carried out by means of a psychophysical method of forced choice of four alternatives. But any other psychophysical method could be used.

The method additionally comprises a fifth stage that can be applied to one or both eyes, where in the fifth stage:

 35

or third ocular refractions are calculated which are comprised between the ocular refraction obtained in the third stage and said ocular refraction of the third stage plus a sphere myoption value (MS) and a cylinder myopia value (MC);

 5

or every third ocular refraction is transformed to a power vector and a metric is calculated, preferably its Euclidean distance (ED) with respect to the ocular refraction obtained in the third stage, the third ocular refractions being ordered ascending according to said metric, preferably Euclidean distance (ED); 10

or the third ocular refractions with the optotype size determined in the fourth stage are shown to the patient until a final ocular refraction of the fifth stage is obtained with final values of sphere (S), power (C) and axis (α).

 fifteen

In accordance with all this, a method is obtained to determine the subjective ocular refraction where the sphere (S), power (C) and axis (α) information of the lenses are shown to the patient in a single scalar, this is a power vector, so that the accuracy of the method is improved and its execution time is reduced compared to conventional subjective refraction methods. twenty

The object of the invention is also a device for carrying out the method capable of changing the sphero-cylindrical power of both eyes quickly and synchronously with the visual stimuli presented and with a control mechanism that allows the patient to enter information into the system. This control mechanism can be an eye-tracker system that detects the position in the visual field in which the patient is fixing his attention or a keyboard.

Description of the figures

 30

Figure 1A depicts a scene shown to the patient during the first stage of monocular visual acuity and the fifth stage of binocular balance, according to a task of forced choice of 4 alternatives.

Figure 1B depicts scenes shown to the patient during the second stage of

Binocular bisection and the third stage of anisometropia testing.

Figure 2A shows a graph with the dependence of the Euclidean distance (ED) with the cylinder value (C) of the most negative refraction (M1, J01, J451).

 5

Figure 2B shows a three-dimensional representation of all possible ocular refractions that are presented to the patient for their choice.

Figure 2D shows a three-dimensional representation of all possible ocular refractions transformed to power vectors. 10

Figures 2C and 2E respectively show a planar representation of Figures 2B and 2D.

Figure 3 depicts a scene shown to the patient for a forced choice task 15 of 8 alternatives.

Figure 4 represents a spatial scene shown to the patient for a task of forced choice of 4 alternatives.

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Figure 5 represents a sequence of time scenes shown to the patient for a task of forced choice of 4 alternatives.

Detailed description of the invention

 25

An ocular refraction consists in the representation of a visual stimulus (optotype) before the eyes of a patient to determine the values of sphere (S), cylinder (C) and axis (α) that define the sphero-cylindrical lenses that result in a better visual acuity for the patient and that allow to correct the defects of his vision.

 30

The sphere (S) is expressed in multiples of 0.25 diopters (D), and refers to the spherical power (S) of the sphero-cylindrical lenses that each patient needs to be able to correct their visual impairment (myopia or farsightedness). The value of the sphere (S) is expressed in a negative sign when there is myopia (-1.00, -1.25, -1.50, ...) and is expressed in a positive sign, or omitted, when there is farsightedness (+1.00, 1.25, +1.50 , ...). 35

The cylinder (C) and the axis (α) refer respectively to the cylindrical power (C) and the orientation of the axis of the cylinder (α) in which the sphero-cylindrical lenses must be placed in front of each eye to correct the astigmatism. The cylinder (C) is expressed in diopters (D) and α axis in degrees. 5

The method of the invention can be applied monocularly, for this it comprises a previous stage of initial ocular refraction, a first stage of monocular visual acuity and a second stage of binocular bisection, however the method can be applied binocularly, for this the method additionally it comprises a third stage of anisometropia check and a fourth stage of monocular visual acuity. Additionally, the method also comprises a fifth stage of binocular balance that can be applied to one or both eyes.

Previous stage: Ocular refraction of onset 15

The subjective ocular refraction method comprises the previous stage where an initial ocular refraction is performed, which is a sphero-cylindrical refraction in negative cylindrical notation (the cylindrical power C is expressed with a negative sign) for both eyes. Through said ocular start refraction, start values are obtained for the sphere (S), the cylinder (C) and the axis (α) of the lenses. If the method is applied binocularly, an initial ocular refraction is obtained for each eye.

As is done in conventional clinical practice, the initial ocular refraction to determine the subjective ocular refraction can be obtained by an autorefractometer, a wavefront sensor, a retinoscopy or a prior medical prescription.

First stage: Monocular visual acuity

After the previous stage of initial ocular refraction, the method of the invention comprises the first stage in which the monocular visual acuity of one or both eyes of the patient is checked using the initial values of the sphere (S), the cylinder (C ) and the axis (α).

For this, in the first stage the patient is subjected to a task of forced choice of 4 alternatives, first the process is performed in one eye and then in the contralateral eye. Se 35

it shows on an screen an optotype with an initial visual acuity, preferably a very low value of visual acuity (for example 0.4 logMAR), so that the patient must correctly distinguish the optotype. In the example of figure 1A as an optotype, a “Snellen” E is shown in the center of the visual field and the patient must correctly determine the orientation of the optotype with the gaze, for this a device 5 is incorporated that incorporates a tracking system of the eye (eye-tracker) that allows to know what orientation the patient is selecting with the look. This process can be repeated several times to reduce the percentage of success by chance. If the patient achieves a certain number of times the distinction of the optotype, the optotype decreases in size (for example 0.1 logMAR), on the contrary, if the patient is not able to correctly discern the displayed optotype, the optotype increases in size. This process is repeated until the patient is unable to correctly detect the optotype, or up to a limited upper limit (for example, the maximum resolution that the screen can display). The best visual acuity obtained with this test in both eyes is used to establish the size of the optotype to be used in the later stages of the method, specifically in the second stage of binocular bisection and in the third stage of anisometropia testing.

Second stage: Binocular bisection

In the second stage, ocular (ref) refractions are determined in which it is assumed that the final subjective ocular refraction will be included, and each refraction is associated with values of sphere (S), cylinder (C) and axis ( α) for the lenses.

In the second stage, six free parameters are determined which are a sphere range value (RS), a cylinder range value (RC), an axis range value (Rα), a value of 25 sphere pitch (PS ), a cylinder pitch value (PC) and an axis pitch value (Pα).

The range values are calculated in comparison with the start values of sphere (S), cylinder (C) and axis (α) of the start refraction of the previous stage, and are values in which it is assumed that it will the final subjective ocular refraction is included. 30

For example, it could be considered that the final subjective ocular refraction could differ from the initial refraction between -0.75 D to +1.00 D for the sphere (S), that is to say a sphere range value (RS) of 1.75 D; ± 0.50 D for the cylinder (C), ie a cylinder range (RC) value of 1.00 D; and ± 10º for the axis (α), that is, an axis range value (Rα) of 20º. 35

These range values determine the duration of the method and are based on the assumption that the initial ocular refraction is close to the final subjective ocular refraction. It is also important to note that the cylinder (RC) and axis (Rα) range values are theoretically bounded, that is, the axis (Rα) cannot vary more than 179º, so that its maximum value goes from 1º to 180º. Regarding the value of cylinder range (RC), it can be expressed in negative or positive notation but both notations cannot be mixed given the inter-relationship between the values of sphere (S), cylinder (C) and axis (α) of the lenses, so that the maximum cylinder range (RC) value is bounded below and can range from any arbitrary value to 0.00 D. 10

After predetermining the range values (RS, RC, Rα), the step values (PS, PC, Pα) must be predetermined, that is the precision, for each sphere variable (S), cylinder (C) and axis (α) from one refraction to another. Typically, 0.25 D can be used as the sphere pitch value (PS) and as the cylinder pitch value (PC) and 5th as the axis pitch value (Pα). fifteen

Once the six free parameters have been predetermined (RS, RC, Rα, PS, PC, Pα), all possible combinations of ocular (ref) refractions within the range values (RS, RC, Rα) can be calculated. ) and with the step values (PS, PC, Pα). twenty

At this point, all ocular refractions are transformed to an orthonormal base with a power vector associated with each refraction, that is, each three values of sphere (S), cylinder (C) and axis (α) are transformed into equivalent spherical (M) and some crossed cylinders of Jackson (J0 and J45). 25

This transformation allows algebraic operations on the values (S, C, α) of each refraction in which each value is independent of the other. It should be noted that the sphere (S), the cylinder (C) and the axis (α) are not independent variables, so that a change in the value of one of them implies an adjustment of the others, however this problem does not exist 30 for variables transformed to power vectors, whereby the method for determining subjective eye repair is faster and more accurate than conventional methods.

To carry out the transformation to an orthonormal base, equations 1, 2 and 3 are used. Note that in these equations the cylindrical power must be expressed negatively.

       [one]

      [2] 5

      [3]

Then the second stage comprises calculating all the Euclidean distances (ED) between all the generated ocular refractions (Mi, J0i, J45i, for i = 1..Nref) with respect to the most negative refraction (M1, J01, J451). M1 being the most negative value among all 10 possible spherical equivalents considered (M) and (Nref) being the maximum number of ocular refractions considered. The subscript i denotes the integer of each ocular refraction generated. Euclidean distance (ED) is calculated according to the following equation:

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    [4]

The maximum number of refractions (Nref) is obtained from the following equation, where rounding () is a function that rounds the argument to the nearest integer and where RS, RC, Rα are the values of range and PS, PC, and Pα are the step values. twenty

   [5]

As can be seen in Figure 2A, once the 6 free parameters (RS, RC, Rα, PS, PC, Pα) have been predetermined, the maximum number of refractions (Nref) depends on the cylinder value (C ) more negative among all those considered. Specifically, Figure 2A shows the dependence of the Euclidean distance (ED) with the cylinder value (C) of the most negative refraction (M1, J01, J451). The specific case with the following free parameters is shown in this graph: RE = 2.00 D, RO = 0º and PE = PC = 0.25 D. The number of possible refractions (Nref) are (in ascending order): 9, 18, 27 , 36 and 45. 30

From this point on, all ocular refractions generated and transformed to power vectors are sorted in ascending order according to the Euclidean distance (ED) previously calculated.

Once this computational process has been carried out to order the power vectors, a double forced task can be carried out inspired by a bisection algorithm, which belongs to the field of mathematical root search algorithms. For this task in which the response of the patient will intervene, the ocular refractions transformed to power vectors are shown to the patient until a final ocular refraction of the second stage is obtained according to final values of sphere (S), power (C) and axis (α). 10

For this, the patient is presented with an Snellen optotype E (Figure 1B) for example 4 seconds with an ocular refraction given by one of the ends of the entire range of ordered refractions, after 4 seconds the same optotype is presented with ocular refraction opposite the range of ordered refractions. That is, the first pair of refractions can be the one associated with the power vector M1, J01, J451 and the second one can be the one associated with the vector MNref, J0Nref, J45Nref. It should be noted that the decision to present a refraction in the first or second place is preferably randomized. The size determined in the first stage of the method is used as the optotype size. twenty

Once the two pairs of refractions have been presented, the patient is required to respond which image (refraction) he perceives most comfortably by indicating the right or left direction (for example, by pressing the arrow keys on a keyboard) where each direction corresponds to select the first or second refraction presented. When selecting one of them, in the next pair of images to compare the refraction that has not previously been selected, it is changed by the refraction corresponding to the average of the index of rounded refractions to the nearest integer. That is, in the first pair of images (refractions) to compare, both pairs of refractions correspond to the index imin = 1 and imax = Nref, while in the second selection, these indexes correspond to imin or imax = rounding ((Nref + 1) / 2) and imax = Nref or imin = 1 (depending on whether the patient has selected the refractive index imax = Nref or imin = 1). In addition to this root search algorithm to approximate the correct result of subjective refraction, the method can use other root search algorithms such as the Brent, Newton, secant, interpolation, polynomial algorithm, etc. 35

This procedure is repeated until imin = imax. In order to reduce the percentage of error by chance, each comparison of refractions can be repeated a certain number of times, for example 3. Finally in this second stage a final ocular refraction is obtained according to final values of sphere (S) , power (C) and axis (α), which is the ocular refraction that results in better visual acuity for the patient.

When the method is applied binocularly the steps of the second stage for each eye are repeated, consequently obtaining an ocular refraction for each eye, which will not be the final subjective ocular refraction since in addition a third stage of anisometropia check is performed, a fourth stage of monocular visual acuity and a fifth stage of binocular balance.

Figures 2B and 2D respectively show a three-dimensional representation of all possible sphero-cylindrical refractions and of these same transformed to 15 power vectors, considering the specific case for RS = 2.00 D, RC = 1.00 D, Rα = 0º, PS = Pα = 0.25 D and a refraction in both eyes of -3.00-1.50x90º. Note that since Rα = 0º, all refractions are included in planes (α = 90º in Figure 2B and J45 = 0 D in Figure 2D). These planes are shown in Figures 2C and 2E. Each point represents a refraction and the line connects each refraction in ascending order of Euclidean distance 20 with respect to the most negative refraction.

Third stage: Anisometropia check

Following the second stage, the method of the invention additionally comprises the third stage where it is checked whether anisometropia exists. Anisometropia is defined as the difference in refraction between right and left eye, so this function aims to reduce inter-eye error, understanding this error as the differences in both sphere and cylinder between right eye and left eye that are not they are due to physiological anisometropia but to a measurement error in the refraction of the beginning of the method. 30

In the third stage it is checked whether anisometropia exists, both in sphere (S) and in cylinder (C), of at least 0.25 D or more. This third stage uses the output parameters of the second stage as input parameters, so the final sphere values are compared

(S), power (C) and axis (α) obtained in the second stage with the start values of sphere (S), the cylinder (C) and the axis (α) obtained in the previous stage.

For example, if the optimal ocular subjective refraction of a patient obtained in the second stage is for the right and left eye respectively, -2.75 and -2.00 D (refractions 5 only with spherical component) and the starting refractions obtained in the previous stage they are respectively -2.75 D and -1.75 D. There is a physiological anisometropia of 0.75 D and there is an inter-eye error in a sphere of 0.25 D that comes from the start refraction.

Thus, in the third stage in a first step, a maximum inter-eye error in 10 sphere (EIOS) and a maximum inter-eye error in cylinder (EIOC) are presumed to be derived from the two starting refractions obtained in the previous stage (one referring to the right eye and another referring to the left eye) with respect to the ocular refraction obtained in the second stage.

In a second step, second ocular refractions obtained from all the possible combinations of refractions between the refraction of the right eye and the refraction of the left eye obtained in the second stage are calculated. For this, the same ball pitch (PS) and cylinder (PC) values defined in the second stage are used and as sphere range (RS) and cylinder (RC) values those between the right eye refraction and the left eye refraction obtained in the second stage 20

In a third step, analogously to the second stage, all second ocular refractions are transformed to power vectors and the Euclidean distance (ED) of each of them is calculated with respect to a reference refraction selected from one of the 25 second ocular refractions obtained in the second step (for example, the right eye).

Next, at least three pairs of the second ocular refractions transformed to power vectors are selected to compare them with the ocular refraction 30 obtained in the second stage of binocular bisection, for which the patient is subjected to three forced double tasks. Each of these double forced tasks can be repeated a certain number of times (for example 3 times) in order to reduce the percentage of false positives given by the patient.

 35

First, a selected pair of the second ocular refractions is compared with the ocular refractions for each eye obtained in the second stage to reduce the inter-eye error (EIOS, EIOC) of the left eye, for this in the double task forced to the that the patient is subjected to only changes the refraction of the right eye, while that of the left eye remains invariant. 5

Secondly, another selected pair of the second ocular refractions is compared with the ocular refractions for each eye obtained in the second stage to reduce the inter-eye error (EIOS, EIOC) of the right eye, for this in the double task forced to the that the patient undergoes only the refraction of the left eye is changed, while that of the right eye remains invariant.

Finally, another selected pair of the second ocular refractions is compared with the ocular refractions for each eye obtained in the second stage to reduce the inter-eye error (EIOS, EIOC) of both eyes, for this in the double forced task to The one submitted to the patient changes the refraction of both eyes.

After these comparisons, an ocular refraction is obtained for each eye with values of sphere (S), power (C) and axis (α) according to the patient's responses. Note that it could be the case of obtaining contradictory answers, in which case no change would be made.

Fourth stage: Monocular visual acuity

The method additionally comprises the fourth stage where the size of an optotype is determined according to the best monocular visual acuity of the patient, this stage is performed analogously to the first stage, but in this case the optotype selection is performed for the values of sphere (S), power (C) and axis (α) of the ocular spare parts obtained in the third stage of anisometropia check.

 30

Fifth stage: Binocular balance

The method additionally comprises the fifth stage of binocular balance in which third ocular refractions are calculated that are comprised between the ocular refraction obtained in the third stage of anisometropia checking and said refraction 35

ocular the third stage plus a value of sphere myopia (MS) and a value of cylinder myopia (MC), where the value of sphere myoping (MS) is added to the sphere value (S) of ocular refraction the third stage and the value of myopicization in cylinder (MC) is added to the value of cylinder (C) of ocular refraction the third stage. As in the second stage, the third ocular refractions are calculated with the step values (PS, PC, 5 Pα) of said second stage.

From then on, each third ocular refraction is transformed into a power vector and its Euclidean distance (ED) is calculated with respect to the ocular refraction obtained in the third stage of anisometropia check, ascending the 10 third ocular refractions in ascending order. its Euclidean distance (ED).

Next, the patient is presented with the third most positive ocular refraction (see Figure 1A), that is, the one with the highest value of myopia in sphere (MS) or cylinder (MC), using the optotype size identified in The fourth stage fifteen

The patient must correctly distinguish the optotype, if he does not succeed, myopia decreases one step, that is, the next third refraction closest to the third refraction that is being represented from all previously calculated is presented. To reduce the percentage of success by chance of the patient, the process can be repeated several 20 times. The fifth stage ends when the patient is able to properly determine the presented optotype, or if the limit refraction in the calculated range had been reached. The third ocular retraction obtained with its values of sphere (S), power (C) and axis (α) in the fifth stage is the final subjective refraction resulting in a better visual acuity for the patient. The fifth stage can be performed on one or both eyes of the patient.

In the first, fourth and fifth of the method a psycho-physical response of the patient is obtained through a forced task of 4 alternatives, as shown in the preferred embodiment of Figure 1A, however, the same result could be reached by means of a forced task of n-alternatives, where each alternative is arranged radially on a display, for example, by a task of 8 alternatives the percentage of successes by chance decreases from 1/4 to 1/8 increasing the accuracy of the final result. Figure 3 shows an example of the configuration on the display of an 8-alternative task.

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In the second and third stages of the method, the psychophysical response is obtained through a forced task of 2 alternatives, as shown in the preferred embodiment of Figure 1B, however, the same result could be reached by a forced task of n -alternatives, where each alternative is presented spatially (figure 4) or temporarily (figure 5) on the display. For the spatial case, the stimuli would be presented radially 5 as in Figure 4 and by following the eyes (eye-tracker) the spherocylindrical refraction would be adjusted each time the patient's gaze falls on the area that comprises each stimulus. For both the temporal and spatial case, the selection by the patient of the refraction would be done by tracking the gaze preferably (although the value of the selection could be entered by means of a keyboard). 10 Figure 4 and 5 show the specific case of 4 spatial and temporal alternatives, respectively.

The metric that is used to unify spherocylindrical refraction in a single scalar is preferably Euclidean distance (ED), however, any other more elaborate metric could be used capable of summarizing the information of spherocylindrical refraction in a single scalar. For example, the Visual Strehl Ratio of the Optical Transfer Function (RSVFTO) can be used, which can be calculated using the following equation:

 twenty

where FTO is the optical transfer function for all spatial frequencies with any orientation (fx, fy);

LD is "limited by diffraction"; Y

FSCN is the neural contrast sensitivity function, calculated according to the following equation:

where FSC is the contrast sensitivity function that incorporates both neural and optical effects for all spatial frequencies with any orientation (fx, fy); Y

FTM is the modulation transfer function for all spatial frequencies with any orientation (fx, fy).

It should be noted that any list of values of sphere (S), power (C) and axis (α) can be described by a wavefront from which, for a given value of 5 pupillary diameter and wavelength, and by Using Fourier optics, the optical transfer function can be obtained, as well as the modulation transfer function.

Claims (9)

1.- Method to determine the subjective ocular refraction in an automated way, characterized in that it comprises at least:  5  a previous stage where an ocular start refraction is obtained according to the start values of sphere (S), power (C) and axis (α);  a first stage where the size of an optotype is determined according to the best monocular visual acuity of a patient for the values of onset of sphere (S), power (C) and axis (α);  a second stage where: or predetermined values of range of sphere (RS), of cylinder (RC), and of axis (Rα), 15 and values of passage of sphere (PS) of cylinder (PC) and of axis (Pα); or ocular refractions are calculated within the range values (RS, RC, Rα) and with the pass values (PS, PC and Pα);  twenty or each ocular refraction is transformed into a power vector with values of sphere (S), power (C) and axis (α), said values being transformed to a spherical equivalent (M) and Jackson's crossed cylinders (J0 and J45) according to the following equations:         25 or a metric is calculated for each ocular refraction;  30 or the ocular refractions transformed to power vectors are ordered according to the previously calculated metrics; or the patient is shown ocular refractions with the optotype size determined in the first stage until obtaining a final ocular refraction of the second stage with final values of sphere (S), power (C) and axis (α). 2. Method for determining the subjective ocular refraction in an automated manner, according to the preceding claim, characterized in that the metric for ordering the ocular refractions is the Euclidean distance (ED), such that or a Euclidean distance (ED) is calculated for each ocular refraction according to the following equation:      10 the subscript i being the integer of each ocular refraction. or the ocular refractions transformed to power vectors are ordered in ascending order according to the Euclidean distance calculated previously;  fifteen or the patient is shown ocular refractions with the optotype size determined in the first stage until the final ocular refraction of the second stage is obtained with final values of sphere (S), power (C) and axis (α). 3. Method for determining the subjective ocular refraction in an automated way, according to any one of the preceding claims, characterized in that the method is performed binocularly, wherein in the previous stage an initial ocular refraction is performed for each eye of the patient. , and in the second stage a final ocular refraction for each eye. 4. Method for determining the subjective ocular refraction in an automated way, according to any one of the preceding claims, characterized in that the number of ocular refractions is calculated according to the following equation:    [5]  30 where RS, RC, Rα are the range values and PS, PC, and Pα are the step values, and where rounding () is a function that rounds the argument to the nearest integer. 5.- Method to determine the subjective ocular refraction in an automated way, according to the The preceding claim, characterized in that the ocular refractions are shown to the patient consecutively in pairs, the patient having to select a refraction of each pair, wherein the refractions of the first pair correspond to the refractions for imin = 1 and imax = Nref, while that the following pairs of refractions correspond to the refractions for imin = rounding ((Nref + 1) / 2) and imax = Nref, or imin = 1 and 5 imax = rounding ((Nref + 1) / 2). 6. Method for determining the subjective ocular refraction in an automated way, according to any one of claims 3 to 5, characterized in that it additionally comprises a third stage where it is checked whether there is anisometropia, both in sphere (S) and in cylinder 10 (C), for this: or a maximum inter-eye sphere error (EIOS) and a maximum inter-eye cylinder error (EIOC) are preset;  fifteen or second ocular refractions are calculated between the refraction of the right eye and the refraction of the left eye obtained in the second stage using the ball pitch (PS) and cylinder (PC) values defined in the second stage; or each second ocular refraction is transformed to a power vector and its Euclidean distance (ED) is calculated with respect to a reference refraction selected from one of the second ocular refractions; or three pairs of the second ocular refractions transformed to power vectors are selected and compared with the second ocular refractions to reduce the inter-eye error (EIOS, EIOC), obtaining an ocular refraction for each eye with sphere values ( S), power (C) and axis (α). 7. Method for determining the subjective ocular refraction in an automated manner, according to the preceding claim, characterized in that it additionally comprises a fourth stage 30 in which the size of an optotype is determined according to the best monocular visual acuity of a patient for values of sphere (S), power (C) and axis (α) of the ocular refractions obtained in the third stage. 8.- Method to determine the subjective ocular refraction in an automated way, according to the previous claim, characterized in that it additionally comprises a fifth stage wherein: or third ocular refractions are calculated that are comprised between the ocular refraction obtained in the third stage and said ocular refraction of the third stage plus a sphere myolation value (MS) and a cylinder myoization value (MC), or each third ocular refraction is transformed into a power vector and its Euclidean distance (ED) is calculated with respect to the ocular refraction obtained in the third stage, the third ocular refractions being ascending ascending according to its Euclidean distance (ED); or the third ocular refractions with the optotype size determined in the fourth stage are shown to the patient until a final ocular refraction of the fifth stage is obtained with final values of sphere (S), power (C) and axis (α). 9. Device used to carry out the method defined according to any one of the preceding claims.