Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
  • A61B3/1015—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for wavefront analysis

Definitions

• the invention relates to a method for determining the required correction of the refractive error of an eye according to claims 1, 2 and 3 and a corresponding arrangement for determining the required correction of refractive error of an eye according to claims 20, 21 and 22.
• the invention relates to a computer program , a computer program product and a computer for carrying out the method according to the invention.
• the defective human eye has refractive errors that can be described in a first approximation in terms of sphere, cylinder and axis. It is assumed that the refractive error of the eye can be approximately corrected by a lens with a toric surface. This approximation is sufficient to correct for erroneous deflection of light rays striking the pupil center of the eye.
• the information obtained from a wavefront refractor can be used to develop improved vision aids or vision correction methods.
• the best known example of a vision correction procedure is wavefront guided refractive surgery. With this treatment, a volume of any geometry from the
• Such a correction is with vision aids, such as a spectacle lens or a contact lens, not or only partially possible.
• the special feature of a spectacle lens is that the eye must look through different areas of the lens.
• a complete correction of higher-order errors in a spectacle lens is only possible for a specific viewing direction. As soon as the eye looks in a different direction, the correction of the higher order errors is no longer adjusted and worsens the visual acuity. Furthermore, a complete correction of the higher order errors in a spectacle lens would lead to unacceptable distortions outside the range of this correction.
• the wavefront measurement technology can lead to improved spectacle lenses:
• Subjective refraction is usually performed under daylight conditions with high-contrast optotypes. This leads to refraction values which are optimized for these conditions, in particular for good illumination and for high contrast. This refraction is not suitable for many people watching or watching at dusk. Wavefront measurement can be done in the dark or under mydriatic conditions. This information is obtained for a much larger pupil, which, for example, the determination of an objective refraction (in particular the objective second-order refraction), which is also suitable for mesopic or scotopic light conditions.
• spectacle lenses in particular progressive lenses, have intrinsic aberrations. These intrinsic aberrations can be combined with the measured wavefront of the eye to calculate and produce improved eyeglass lenses. These spectacle lenses can, for at least one particular viewing direction, permit at least partial correction of the higher-order aberrations of the eye-spectacle lens system.
• EP 1 324 689 B1 describes a system for determining a correction for correcting aberrations in an eye of a patient.
• the system includes a computing device to determine the correction of the data signals such that when the correction is applied to the eye, an image quality metric on an image plane of the eye is objectively optimized.
• the computing means in a first step defines a search space (ie, values which may take the coefficients) comprising a plurality of sets of coefficients (eg, sphere, cylinder, axis, or the corresponding Zernike coefficients).
• the previously selected image quality metric eg, Strehl ratio, dot blur function variance, dot image blur function energy, etc.
• the optimum value of the image quality metric is selected from all the values of the image quality metric calculated in the second step, and in a fourth step, the correction is made in accordance with one of the plurality of sets of coefficients for which optimal value of the image quality metric was calculated in the third step.
• LN Thibos et al. describe in their paper "Accuracy and precision of objective refraction from wavefront aberrations", which was published in the Journal of Vision (2004) 4, 329-351 on April 23, 2004, a variety of other objective methods for determining the refraction from a wavefront measurement.
• the eye is not a static system like the classical optical systems; it has the capacity of accommodation.
• the human lens alters both its shape and its position to change the power of the eye as a whole.
• the accommodation process is a continuous process whereby the eye-brain system constantly searches for stimuli to constantly generate the best image. This means that the total refractive power of the eye is subject to high-frequency changes.
• the aberration structure of the eye also changes with the accommodation of the eye. Spherical aberration in particular becomes more negative with accommodation on average. A goggle corresponding to the objective or subjective refraction value is therefore often not perceived as optimal by the wearer.
• the object of the invention is therefore to provide a method and an arrangement for determining the required correction of the refractive error of an eye, which take into account the physiology of the eye on the basis of, for example, a measurement of the wavefront of the eye in the calculation of a vision correction.
• optical correction is meant in particular the strength of a spectacle lens or a contact lens but also the extent of a local ablation of natural components of the refractive eye.
• This object is achieved by a method for determining the required correction of the refractive error of an eye with the features of claims 1, 2 or 3 and an arrangement for determining the required correction of refractive error of an eye with the features of claims 20 and 21 and 22, respectively ,
• the method for determining the required optical correction of the refractive error of an eye presupposes that the optical correction is computationally varied within a target or search space.
• This destination or search space need not be known. It is possible that the optical correction is varied until a termination criterion is met.
• an abort criterion may be the achievement of an optimum or a value very close to that optimum of a target criterion given below.
• the optical correction is now selected within the target area as the required optical correction, in which the caustic satisfies an optical correction and eye-transmitting light beam in the region of the retina of the eye predetermined requirements.
• the optical correction is selected in which the quality or qualities, in particular the volume, of the caustic of a light beam propagating through the optical correction and the eye in the spatial environment of the retina of the eye satisfy predetermined requirements.
• the target or Sollkaustik need not necessarily always be reached, but this may possibly only come very close. Kaustik is the more or less narrow constriction of a beam that arises instead of a pixel, which shows the outgoing beam from an object point due to aberrations before it diverge again.
• Threshold exceeds or within a range of the optimum value. This method differs from that known from the prior art, in which the optical correction is chosen such that the second-order refraction is optimized only for one image plane of the eye.
• the inventively designed according to the corresponding independent claim 20 arrangement comprises an analysis device to select the optical correction within the search space as a required optical correction, in which the Kaustik a passing through optical correction and eye light beam in Area of the retina of the eye meets the above-described predetermined requirements.
• inventive method for determining the required optical correction of the refractive error of an eye according to the independent claim 2 comprises the following method steps:
• the refractive properties of the eye are provided.
• the eye is preferably located in a predetermined state of accommodation. It has been found to be beneficial when the eye is focused at infinity, i. when the visual rays of the eyes do not converge to a point nearby.
• the refractive properties of the refractive eye can be e.g. be determined in advance by measuring the wavefront of the eye to be corrected. This process is also known in English as "generating a wavefront aberration map.” Specifically, such a wavefront measurement can be performed by the so-called Shack-Hartmann method or by the so-called Tscherning method The projection of a light beam (Hartmann-Shack) or a light spot pattern (Cherning) on the retina is followed. The course of the reflected rays in the optical system under wavefront conditions is tracked.Virror changes of the rays, or a different image from the original pattern after leaving the optical system are displayed The deviation of this wavefront from the ideal case is called an aberration and can be measured with an aberrometer.
• the Hartmann-S hack method generally uses a CCD camera to capture images, details of which are given, for example thesis of G. M. Spitzlberger "Change of the optical aberrations of the human eye by laser in situ keratomileusis" from
• the so-called ray-tracing method can also be used to determine the refractive power errors of the optically-defective eye.
• a very fine laser beam is scanned through the pupil of the eye to the retina.
• Each laser spot can be identified as a reflex on the macula become. The location and shape of this image on the macula allows conclusions about the refraction and visual quality.
• the refractive properties of the (human or animal) eye can also be determined by measuring the tomography of the eye. Specifically, the geometries of the optically active surfaces of the eye are measured; possibly including the refractive indices of the individual media.
• quantities of parameter sets describing the optical correction are determined. These sizes may e.g. consist of sphere, cylinder and axis or include these. It is also possible for the quantities to include so-called area descriptions or subsets of these area descriptions such as splines, Taylor developments or Zernike developments or individual coefficients of these developments.
• the computer technology allows, as quantities describing the optical correction, the coefficients of an algebraic basis or area representation suitable for the description of the optical correction, such as e.g. Spline, Zernike, or Taylor coefficients.
• a third step it is provided to provide a suitable method for determining a target parameter set from the parameter sets, which provides the optimum optical correction for the refractive properties of the eye provided or determined in the first step, which meets the given requirements.
• this optical correction will be referred to as optical target correction or for the case of an optimization method described below as optimum optical correction.
• a Newton-Raphson method for example, a Newton-Raphson method, a hill climbing method or an "all-tried method" in which all parameter sets contained within a search space of parameter sets have been checked for the given requirements, in particular for an optimum, have proved suitable.
• the above three steps do not define a time order, but it does not matter which of the three steps is provided first and in what sequence the corresponding information. It is only important that the information for the subsequent process to determine the optical target correction, in particular the optimal optical correction are available.
• a (subsequent) fourth step at least two sub-metrics in different assigned stages of propagation of light by the eye and optical correction comprehensive optical system for one of the parameter sets are now determined.
• the light passes through the optical system eye / correction.
• the deviation of the light beam expressed in each case by a quality metric (sub-metric), from the ideal case is considered when it has passed through the eye or the eye / correction system (propagated).
• a propagation in the opposite direction ie by the system eye / correction in the direction of the object is conceivable. This propagation is not fixed in a fixed direction by the system eye / correction, but can be carried out for any number of directions (in general viewing directions).
• these sub-metrics may include beam quality metrics, such as beam quality metrics. Metrics that are the Strehl ratio or the power of the point image blur function included within the Airy slice. It is also possible that the sub-metrics have geometric metrics, such as e.g. those that account for the mean curvature of the wavefront are.
• a total metric in particular the quality of the caustics reflecting (Kaustikmetrik) is determined from a weighted sum of the previously determined sub-metrics. It is possible that all sub-metrics are weighted equally when determining the total metric (caustic metric). However, it has proven to be favorable if a sub-metric of a preferred propagation stage is weighted more heavily than the sub-metrics in the propagation stages before and / or after this preferred propagation stage.
• the sub-metric for the image on the retina (corresponding to the sub-metric in the preferred propagation stage) would be more weighted than the sub-metric for an image in front of or behind the retina of the eye.
• the weighting could be eg 60/40.
• the sub-metrics in the propagation stages before and / or behind the preferred propagation stage are weighted less with increasing distance from the preferred propagation stage.
• the sub-metric for the image on the retina corresponding to the sub-metric at the preferred propagation stage
• the sub-metric for an image 0.5d before or behind the retina would be weighted more heavily than the sub-metric for an image at 1d from the retina.
• the weighting could e.g. 50/30/20, if no sub-metric is taken into account before the retina, but behind the retina two further sub-metrics in different image levels are included in the calculation. Likewise, it is possible to take the object plane when propagated in the direction of the object as the preferred propagation stage.
• the intensity distribution in the three-dimensional space of the beam is calculated using a modified Nijboer-Zernike formalism (continuum of sub-metrics) and the energy density along this intensity distribution is used as a parameter for determining the target parameter set, in particular for optimizing the optimal parameter set.
• steps four and five are performed for all parameter sets required to determine the target parameter set according to the method provided in step three.
• the target parameter set is selected from the parameter sets for which steps four and five have been performed, which provides the target total metric (target caustic metric) that satisfies the specified requirements.
• target caustic metric target caustic metric
• the optimal total metric is generally the metric with the maximum (or slightly different) value.
• a final target parameter set is calculated that provides the final target metric (e.g., final optimal metric) from weights of all previously determined target total metrics (e.g., optimal total metrics) for the different accommodation states of the eye.
• the required optical correction is determined from the (final) target parameter set (e.g., optimal (final) parameter set selected in step seven or, if appropriate, the different accommodation states of the eye).
• the (final) target parameter set e.g., optimal (final) parameter set selected in step seven or, if appropriate, the different accommodation states of the eye.
• the arrangement according to the invention for determining the required optical correction of the refractive error of an eye comprises an input device for providing the refractive properties of the eye and an analysis device.
• the analysis device is provided initially to determine at least two sub-metrics in different associated propagation stages of a light beam through the eye and correction of the optical system for a parameter set of the variables describing the optical correction. From a weighted sum of the sub-metrics, the analyzer then determines an overall metric. This process of determining sub-metrics and subsequent calculation of an overall metric is performed by the analysis device for further parameter sets of the optical correction descriptive quantities repeated, which are required to determine a target parameter set (eg optimal parameter set).
• a target parameter set eg optimal parameter set
• the analyzer is further configured to select the target parameter set (eg, optimal parameter set) from the parameter sets for which the sub-metrics determination process and subsequent calculation of an overall metric has been performed that provides the target total metric (eg, optimal total metric).
• the analysis device is also designed to determine the required optical correction from the target parameter set selected in the previous step (eg optimal parameter set).
• the arrangement according to the invention has an output device in order to be able to output the information defining the optical correction to a user in a detectable manner.
• the input device may comprise, for example, a keyboard, to which certain information about the refractive properties of the eye can be supplied by a wavefront measurement.
• the input device may be provided with a wavefront measuring device for measuring the refractive properties of the eye (wavefront refractor) and / or with an aberrometer according to the Shack-Hartmann principle and / or with an aberrometer for the Cherning method and / or with a tomograph for the eye and / or an aberrometer operating according to the ray-tracing method via a suitable interface.
• a wavefront measuring device for measuring the refractive properties of the eye (wavefront refractor) and / or with an aberrometer according to the Shack-Hartmann principle and / or with an aberrometer for the Cherning method and / or with a tomograph for the eye and / or an aberrometer operating according to the ray-tracing method via a suitable interface.
• FIG. 1 shows a human refractive eye with a spectacle lens, wherein the
• FIG. 2 shows a human refractive eye with a spectacle lens, wherein the
• Breaking properties of the spectacle lens according to the invention are chosen such that the caustic of an incident light beam in the eye is optimally optimized in the retina of the eye,
• Figure 3 the human eye of Figure 2 with a schematic representation of
• FIG. 1 shows a defective human eye 1 with a spectacle lens 2 in cross section.
• a bundle 3 of parallel light beams 3a, 3b, 3c, 3d, 3e enters the eye 1 via the spectacle lens 2.
• the iris 4 limits the amount of incident light.
• the light beams 3a, 3b, 3c, 3d, 3e are imaged in a non-ideal manner on the retina 6 of the eye 1 due to the non-ideal refractive power of the optical system comprising the spectacle lens 2 and the eye lens 5.
• the procedure may cause the image quality outside of this level 7 to drop very rapidly. Such a drop may e.g. occur very quickly at high spherical aberrations. For the eye, this would be an extraordinary effort, since the accommodative state of the eye must be kept very accurate in order to obtain good image quality.
• this problem is solved by optimizing the caustic 8 of the light beam 3 about the image plane 7, ie plane on the retina 6, onto which the light beam 3 is imaged (see FIG.
• This procedure could, for example, increase the depth of field of the image.
• the image quality on the image plane 7 itself could possibly be slightly worse than the optimum achievable there. But this measure ensures a more pleasant and symptom-free visual impression, because fluctuations in the eye are eliminated.
• the optimization of the caustic can be carried out, for example, as follows:
• a so-called "wavefront aberration map" of the eye located in a given state of accommodation is determined.
• a wavefront measurement is carried out for a specific predetermined pupil area.
• a search space of sets is determined for the optical correction of descriptive quantities, such as sphere, cylinder, axis. Furthermore, a picture quality metric for each sentence within this search space, which represents a measure of the image quality resulting from the application of the optical correction 2 to the eye 1 in the image plane 7 of the eye 1, is determined.
• the image quality metrics are determined for each sentence within the search space.
• FIG. 3 shows the point beam functions 11, 12, 13 in the above-mentioned planes 7, 9, 10 of a human eye 1 in order to clarify this situation.
• a caustics metric representing a measure of the caustics in the area of the three levels 7, 9, 10 is calculated for each parameter set within the search space.
• This caustic metric is thus a measure of the quality of the caustic for the respective parameter set.
• the optimal total metric i. Kaustik with the highest quality, selected.
• the required optical correction i. the refractive power distribution of the spectacle lens 2 or the wavefront of the spectacle lens 2 is finally determined taking into account the sentence from which the selected optimum total metric results.
• “aberration maps” can also be used for several Accommodation conditions are determined and the above procedure for all accommodation conditions are performed.
• the above-described optimization process can be improved by not only using the wavefront of the eye for the distance.
• the above optimization process can be repeated for the different wavefronts for different accommodation states. This results in a visual correction, which in addition to the remote optimization also includes an optimization of proximity.
• the quality of the caustics around the image plane may e.g. also be determined by ray tracing assuming a suitable eye model.
• different metrics can be applied, e.g. the diameter of the caustic enclosing more than a certain proportion of the energy, or the amount of energy that arises in a certain area around the optical axis, or other metrics.
• the above optimization process also takes into account the intrinsic aberrations of the spectacle lens.

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