WO2012054651A2

WO2012054651A2 - Methods and systems for customizing refractive corrections of human eyes

Info

Publication number: WO2012054651A2
Application number: PCT/US2011/056956
Authority: WO
Inventors: Junzhong Liang
Original assignee: Krypton Vision, Inc.
Priority date: 2010-10-20
Filing date: 2011-10-19
Publication date: 2012-04-26
Also published as: WO2012054651A3

Abstract

A method for mitigating astigmatism of an eye includes measuring refractive errors, determining a refractive prescription, and fabricating an aspheric lens based on the refractive prescription, where the refractive errors include a focus error and a cylinder error. The refractive prescription includes a focus power that is approximated to the measured focus error and also includes a spherical aberration for mitigating cylinder error of an eye. Also disclosed is a method for prescribing refractive corrections of an eye that includes objectively measuring an eye's wave aberration, subjectively measuring the eye's focus error, specifying a refractive prescription for a customized lens, determining a residual wave aberration, and computing and displaying the computed image metrics. The customized lens prescription includes an artificially induced spherical aberration.

Description

METHODS AND SYSTEMS FOR CUSTOMIZING REFRACTIVE CORRECTIONS OF

HUMAN EYES

RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 61/455,326, filed October 20, 2010, and entitled "Methods and Systems for Customizing Refractive

Corrections of Human Eyes," which is hereby incorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

[0002] Refractive corrections for human eyes can be characterized into two general categories. The first category is the conventional method of vision correction which corrects for an eye's focus error and cylindrical error as measured using a manifest refraction. This conventional method of vision correction, having been in clinical practice for more than a century, is conceptually limited to a correction of just focus error and cylindrical error. In addition, it is also constrained by the subjective nature of how the manifest refraction determines the eye's refractive errors, particularly the eye's cylindrical error. The inaccuracy of the conventional vision correction method using a manifest refraction leads to a situation where there may be significant differences in a refractive prescription of the same eye by different practitioners, as well as in a coarse resolution of cylindrical power— as large as 0.25 Diopters— universally prescribed for conventional vision correction. Correcting an eye's astigmatism using conventional vision correction is further complicated by the high tolerance in fabricating conventional spectacle lenses. As illustrated in the British standard for tolerances on optical properties of mounted spectacle lenses, BS 2738-1 : 1998, the tolerance of cylindrical power ranges from ±0.09 D for low power lenses to ±0.37 D for high power lenses. Thus, uncorrected astigmatism by today's ophthalmic lenses is as large as 0.37 D due to the combined errors in the manifest refraction and the tolerances associated with making ophthalmic lenses. [0003] The second category is wavefront-guide vision correction which provides correction for all aberrations in an eye, including focus error, cylindrical error, spherical aberration, coma, and others, measured using an objective wavefront sensor. Advanced wavefront sensing that provides reliable measurement of all aberrations in an eye with an objective wavefront sensor is known in the art. In theory, wavefront-guide vision correction could provide perfect aberration-free refractive correction for every eye, because all aberrations can be measured objectively. In reality, however, wavefront-guide vision correction also has its challenges. First, manufacturing a lens with precise control of all aberrations across the lens can be complicated and expensive, because it is impossible to use the conventional processes for manufacturing spherical lenses, toric lenses, and aspheric lenses. Second, wavefront corrections require precise wavefront alignment between a lens and an eye at all times. The combination of these issues in lens manufacturing and in wavefront sensing makes it very difficult to achieve wavefront-guided corrections for conventional lenses such as spectacles, contact lenses, and implantable lenses.

[0004] Recently, Liang proposed another type of refractive correction that was formulated based on new discoveries of optical aberrations in eyes with exceptional visual acuity of 20/10. Liang's method provides astigmatism-free customized refractive correction with subjectively optimized focus error. It involves a) obtaining an objective and precise measurement of cylindrical power in a resolution between 0.01 D and 0.10 D in an eye using an objective aberrometer, b) reliably relating the cylindrical axis obtained from the objective aberrometer to that in a phoroptor, c) determining an optimized focus error of an eye through subjective refraction with a phoroptor, d) generating a customized refraction by combining the objective measured cylindrical power, the objective measured cylindrical axis, and the subjectively measured focus power, e) fabricating a custom lens with a tolerance finer than 0.09 D based on the generated customized refraction, and f) delivering an ophthalmic lens that can provide an astigmatism-free refractive correction for an eye.

[0005] Astigmatism-free customized refractive correction can be achieved with spectacle lenses, but is difficult to achieve for contact lenses because contact lenses are often allowed to move and rotate on cornea of human eyes. For the reason of lens movement, when cylinder error in an eye is less than about 1 Diopter, almost all human eyes with contact lenses today do not have optimized vision because cylinder error in the eye is never corrected. [0006] Additionally, effective correction of an eye's cylinder error with contact lenses must take into account two additional factors: 1) contact lens will be different from spectacle lens because aberrations of an eye can be changed due to the interface between eye's cornea and the posterior surface of a contact lens, 2) contact lenses must maintain its position and orientation on a cornea, which can be achieved through innovated designs for the posterior surface of a contact lens, which can also change focus error and astigmatism in an eye.

[0007] Consequently, although many configurations and methods for vision correction with contact lenses are known in the art, all of them suffer from one or more disadvantages. Thus, there is a need to provide improved methods and devices to achieve optimized vision correction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 shows an exemplary block diagram of a method for mitigating astigmatism of an eye by artificially inducing spherical aberration in an eye in accordance with the present invention.

[0009] FIG. 2 shows an exemplary block diagram of an ophthalmic wavefront system for customizing refractive corrections of an eye.

[0010] FIG. 3 shows an exemplary flow chart of a method of fabricating a custom contact lens for refractive correction of an eye in accordance with the present invention.

[001 1] FIG. 4 shows an exemplary block diagram of a method for wavefront

customization of an eye's refractive corrections in accordance with the present invention.

[0012] FIG. 5a shows averaged modulation transfer factors (MTFs) of human eyes with visual acuity of 20/20 for a focus error of 0D, 1/8D, and 1/4D.

[0013] FIG. 5b shows averaged MTFs of human eyes with visual acuity of 20/10 for a focus error of 0D, 1/8D, and 1/4D.

[0014] FIG. 6 shows an exemplary flow chart of a method for fabricating a custom lens for a refractive correction of an eye in accordance with the present invention.

DETAILED DESCRIPTION

[0015] Methods and system for mitigating astigmatism of an eye by inducing spherical aberration in a refractive correction [0016] Mono-focal refractive corrections for human eyes almost always involve eliminating optical aberrations in human eyes. Removing cylinder error (astigmatism) is critical in improving visual acuity, but is difficult to achieve for contact lenses because contact lenses are often allowed to move and rotate on the cornea of human eyes. For this reason, when cylinder error in an eye is less than about 1 Diopters, almost all human eyes with contact lenses today do not have optimized vision because cylinder error in the eye is never corrected.

[0017] Optical simulations performed in relation to the present patent application discovered that, when cylinder error in a human eye is not corrected at all or is not well corrected, inducing a small amount of spherical aberration into an eye can provide mitigation to the existing cylinder error in an eye. Namely, retinal vision performance for an eye with pure cylinder error existing in the eye will be worse than that for an eye with the existing cylinder error plus a small amount of spherical aberration artificially induced into the eye's optics, because induced spherical aberration makes the retinal point spread function sharper in the image center than that without the induced spherical aberration. More specifically, for eyes with different amounts of cylinder error, different amounts of spherical aberration should be induced into the eye to mitigate vision degradation by cylinder error.

[0018] FIG. 1 shows a block diagram for a method of mitigating astigmatism of an eye with aspheric lens in accordance with the present invention in one embodiment. While the block diagrams in this disclosure shall be described in an exemplary sequence, variations of the sequences, as well as additions to the sequences, are possible without departing from the scope of the invention. First in FIG. 1, refractive errors of an eye are measured, which include at least a focus error (Ds) 10 and a cylinder error (astigmatism, Dc) 11. Second, a refractive prescription 13 is generated for an aspheric contact lens that includes the measured focus error 10 plus a spherical aberration (Co4o) coexisting with a focus offset (Dso) 12 instead of the measured cylinder error. The induced spherical aberration is distributed either in the central pupil with a diameter up to 4.5 mm or across the entire pupil of an eye. Third, a customized aspheric lens 14 is fabricated based on the generated refractive prescription.

[0019] The spherical aberration in the prescription has an optical path difference expressed as a quadric term of the distance from the lens center (p⁴). The prescribed spherical aberration can be further custom determined based on the measured cylinder error in an eye, and has a peak-to-valley value of 1 micron to 10 microns. [0020] Since an eye's aberrations may be altered by contact lenses, in some embodiments the method in FIG. 1 can further include a step of fitting the eye with a test contact lens before measuring the refractive errors of an eye for improved effectiveness. The determined refractive prescription in FIG. 1 in other embodiments can further include a modification based on the known refractive properties of the test contact lens.

[0021 ] Measuring refractive error of an eye (focus error and cylinder error) can be performed using the standard manifest refraction that relies on the subjective response of a patient to a plurality of refractive corrections. Because the cylinder error in an eye cannot be measured precisely using manifest correction, it is thus preferred to measure an eye's cylinder error with an objective device such as a wavefront aberrometer. Due to the fact that the focus errors measured by aberrometers are not accurate due to an eye's accommodation, it is thus preferred to measure focus error in the eye using the manifest refraction.

[0022] Inducing spherical aberration into the human eye for mitigating cylinder error must be carefully performed because induced spherical aberration can degrade vision.

[0023] FIG. 2 shows a block diagram for an ophthalmic wavefront system designed for comparing the customized refractive corrections against the standard corrections in accordance with the present invention.

[0024] In one embodiment, the ophthalmic wavefront system comprises the following three modules: 1) a wavefront sensor module 20 for measuring wavefront slopes across pupil of an eye, 2) a digital processor module 21 that is connected to the wavefront sensor module for computing wave aberration of an eye, and more importantly for providing simulated vision outcomes of a first standard refractive correction 26 and second wavefront-customized refractive corrections 25, and 3) a display module 22 for previewing simulated refractive outcomes of second wavefront-customized refractive corrections 25 in comparison to the first standard refractive correction 26.

[0025] The wavefront sensor module 20 in one embodiment involves producing a light source onto the retina of an eye, as well as converting reflected light across the eye's pupil from the retina to digital signals using an image sensor or a light detector. Digital signals are then fed to a digital processor 21 for wavefront estimation. The wavefront estimation includes: 1) determining wavefront slopes across pupil of an eye by a processor 23, and 2) a least squares estimation of wave aberration 24 of an eye from the measured wavefront slopes. [0026] The first standard refractive correction 26 in one embodiment is represented by refractive correction of a focus error only, while the second wavefront-customized refractive correction 25 is represented by correction of a focus error and an artificially induced spherical aberration and a coexisting focus offset, which are determined based on the cylinder error from the computed wave aberration.

[0027] It must be pointed out that the focus error in the first standard refractive correction

26 can be determined from a manifest refraction or from a wavefront measurement, whereas the focus error in the second wavefront-customized correction 25 is determined from objective wavefront sensing. In simulating refraction outcomes, the difference in the focus error in 26 and 25 should be ignored because the two refractive corrections for the focus error are measurements of the same eye at different accommodation states. The focus error in the first standard refractive correction can be replaced by the focus error in the second wavefront-customized correction in the refractive simulation. However, when a final prescription 29 is generated, the focus error of the second wavefront-customized correction should be replaced by a focus error measured through manifest refraction.

[0028] Providing simulated vision includes 1) determining residual aberrations of an eye

27 based on the computed wave aberration 24 and the first and the second refractive correction separately, 2) computing image metrics 28 from the determined residual aberrations of an eye, which may include simulated acuity charts and retinal contrast distribution(s), and 3) displaying the computed image metrics for previewing refractive outcomes 28 at the display module 22.

[0029] The display module 22 may further provide a prescription for a custom contact lens 29. In one embodiment, the provided prescription is generated by combining some components of the first standard correction 26 and the second wavefront-customized correction 25. Specifically, the focus error of the second wavefront-customized correction is at least in part determined by the first standard correction if the first standard correction is determined from a manifest refraction.

[0030] The wavefront systems in FIG. 2 can also be used for comparing wavefront designs from one measured wave aberration of an eye. In one embodiment, the first standard refractive correction and the second wavefront-customized refractive correction are different only for the focus error that can be used for the simulation of focus tolerance of the second customized correction. In another embodiment, the first standard refractive correction and the second wavefront-customized refractive correction are different only for the astigmatic corrections. Optimization of an eye's astigmatic correction can be performed by an expert based his/her own preference and experience.

[0031] Wavefront-customized refractive corrections with contact lenses

[0032] Mitigating cylinder error in the eye with spherical aberration is suitable only for mono-focal corrections of human eyes that contain a small amount of cylinder error. For eyes with significant cylinder error or for presbyopia treatment of eyes with contact lenses, effective correction of eye's cylinder error is still necessary.

[0033] Effective correction of an eye's cylinder error with contact lenses must take into account two additional factors: 1) contact lens will be different from spectacle lens because aberrations of an eye can be changed due to the interface between eye's cornea and the posterior surface of a contact lens, 2) contact lenses must maintain its position and orientation on a cornea, which can be achieved through innovated designs for the posterior surface of a contact lens, and which can also change focus error and astigmatism in an eye.

[0034] FIG. 3 shows a flow chart of a method of fabricating a custom contact lens for refractive correction of an eye in accordance with the present invention, which include the following steps in one embodiment. First, an eye is fitted with a test contact lens 30. The refraction power of the test contact lens is known, which may contain a focus power Dso and an optional cylinder power. The test contact lens in one embodiment may contain an alignment mark when it has a different refractive power at a different meridian over the test contact lens. Second, astigmatism of the eye fitted with the test contact lens is objectively determined 31 by measuring wavefront slopes of light from the retina of an eye, and the eye's astigmatism is represented by a cylinder power Dc and a cylinder axis a. Third, a focus error of an eye at a far accommodation state 32 is determined subjectively with an acuity chart placed at an optical distance between 3 meters and 15 meters. The final focus error of an eye fitted with a contact lens 33 will include the measured focus error with an acuity chart Ds, and an optional focus offset Do to make the corrected eye slightly myopic or hyperopic. Fourth, a refractive prescription for a customized contact lens 34 is generated by combining the objectively determined astigmatism Dc, the subjectively measured focus error Ds, an optional focus offset Do, and the known refractive power of the test contact lens Dso. Finally, a customized lens 35 can be fabricated to provide optimized vision once a custom refractive prescription is obtained.

[0035] For improved accuracy, determining astigmatism of the eye in one embodiment includes measuring wave aberration of the eye fitted with the tested contact lens for a plurality of times, deriving an optimized astigmatism for the eye for each wavefront measurement, and determining astigmatism of the eye by averaging the repeated measurements. Wave aberration includes not only low-order aberrations such as a focus error and astigmatism but also high-order aberrations such as coma and spherical aberration.

[0036] In another embodiment, the customized refractive prescription in FIG. 3 can further include an addition of a spherical aberration or a distribution of spherical aberration only in the central pupil of an eye for a presbyopic treatment of the eye. A focus offset can co-exist with spherical aberration.

[0037] Improved wavefront optimization of customized refractive corrections

[0038] The wavefront-customized lenses and procedures in the present invention are designed to perform better than traditional lenses or procedures. However, acceptance of these wavefront-customized lenses by patients should not be considered automatic because a lens or a procedure is not engineered/prescribed according to general principles for vision optimization. Neither patients nor clinicians have a clear picture for the final refractive outcomes before a lens or a procedure is realized. It is therefore highly desirable that refractive outcomes of the new wavefront-customized lenses can be compared to those of traditional refractive corrections so that clinicians and patients can make an educated decision.

[0039] In order to address this uncertainty to patients and clinicians, a method of wavefront customization is shown in FIG. 4, which provides graphic illustrations of refractive outcomes before a lens or a procedure is prescribed so that patients and clinicians can make an educated decision about the customized corrections.

[0040] First, optical properties of an eye is measured, which include at least an objective measurement of eye's wave aberration 40 using a device such as an aberrometer, and a subjective refraction measurement of an eye's focus error 41 using a subjective measurement module with an acuity chart. Second, a prescription for a customized lens is generated 42 for one of the two cases: a) a customized aspheric contact lenses, whose prescription is determined by the subjectively measured focus error, an artificially induced spherical aberration and a focus offset coexisting with the induced spherical aberration for mitigating astigmatism in the eye, or b) a customized aspheric lens for the treatment of presbyopia, whose prescription is determined by the subjectively measured focus error, an optional astigmatism that is determined from the objectively measured wave aberration of an eye, and an artificially induced spherical aberration or a distribution of spherical aberrations only in the central pupil of an eye with a diameter less than 4.5 mm. Third, residual wave aberration of an eye 43 is determined based on the measured optical properties of an eye and the generated refractive prescription for a customized lens 42. Fourth, at least one image metrics 44 is calculated from the determined residual wave aberration of an eye, and is displayed for previewing a customized prescription 45. The computed image metrics may include simulated acuity chart(s) and retinal contrast distribution(s). Fifth, a customized refractive prescription for a lens 46 is provided if the computed image metrics is considered acceptable. Finally, a customized lens 47 is fabricated based on a customized refractive prescription. In many cases, a customized design is optimized from a plurality of refractive prescription by changing the prescription 48 and comparing computed retinal images for those prescriptions.

[0041] Even though subjective acuity still cannot be predicted like traditional manifest refraction, the method described in FIG. 4 allows previewing refractive outcomes of a

customized lens reliably because it is derived from wave aberration of an individual eye according to precise physical principles. Seeing simulated vision outcomes can improve confidence for patients as well as for clinicians.

[0042] When applied to a customized contact lens, in some embodiments the method in FIG. 4 may further include a step of fitting the eye with a test contact lens before measuring optical properties of an eye. The refractive powers of the test contact lens can then be included in the generated prescription.

[0043] The wavefront customization can be implemented in many different arrangements. In one embodiment, refractive measurements as well as refractive prescription from steps 40 to 46 in FIG. 4 can be performed at a clinical office, and a refractive prescription can be submitted for ordering a customized lens. In another embodiment, measuring optical properties of an eye - steps 40 through 41 in FIG. 4 - can be performed in a clinical office and is submitted to a remote site for a centralized vision design and vision simulation (steps 42 through 45 in FIG. 4). Simulated vision outcomes 45 can be transmitted by an output module from a remote site to a clinical office for previewing and/or selecting a customized contact lens. Once a customized design is approved, a customized prescription will be transmitted to a system for making a customized lens. An output module may be, for example, a display monitor, a printer, or a computer interface to an external office for communicating a designed refractive correction.

[0044] Method for improving retinal contrast of wavefront-customized refractive corrections

[0045] Current clinical practice for prescribing correction lenses are based on normal visual acuity of 20/20. FIG. 5a shows averaged modulation transfer factors (MTFs) of human eyes with normal visual acuity of 20/20. Three focus offsets from the best focus are considered: 0D, 1/8D and 1/4D. It is clearly seen that an eye's MTF for 20/20 acuity only changes slightly from the perfect focus 0D (curve # 51) to 1/8D (curve # 52) and 1/4 D (curve # 53). Therefore, tolerance in focus error for traditional refractive correction is relatively high, about 0.25D.

[0046] Wavefront-customized refractive corrections allows for creating nearly perfect vision and a complete new population with acuity target of 20/10 or better. Because there is less than about 5% of normal population that has a visual acuity of 20/10, procedures used for conventional clinical practice for 20/20 vision are not suitable anymore.

[0047] FIG. 5b shows averaged MTFs of human eyes with visual acuity of 20/10. Three focus errors are also considered: 0D, 1/8D and 1/4D. It is discovered that an eye's MTF for the 20/10 eyes changes significantly from the perfect focus 0D (Curve # 54) to a focus error of 1/8D (Curve #55) and 1/4D (Curve #56). Therefore, a customized refractive corrections, which is targeted for delivering 20/10 vision, should take into account an eye's micro-fluctuation of accommodation (a focus range of about ±1/8D) as well as the impact of acuity chart at a distance of 3M (1/3D) to 6M (1/6D) in the standard manifest refraction.

[0048] FIG. 6 shows a flow chart of an improved method for customizing refractive lenses for an eye in one embodiment. First, astigmatism of an eye 62 is determined by measuring wave aberration 60 objectively using a device such as a wave front aberrometer. An eye's astigmatism is represented by a cylinder power Dc and a cylinder axis a. Advantages of measuring the eye's astigmatism through objective wave front sensing over the manifest refraction include: a) both cylinder power and cylinder angle can be determined numerically to a higher resolution finer than those in the manifest refraction (1/4D for the focus power, 5 degrees for the cylinder angle), b) determination of the eye's cylinder error is made independent of the eye's focus error and micro-fluctuation of accommodation, which is a limiting factor for the traditional manifest refraction. Second, focus error of an eye at a far accommodation state 61 is determined subjectively with an acuity chart placed at an optical distance between 3 meters to 15 meters. Third, a focus offset Do is added to the focus error Ds determined from the conventional manifest refraction 63 to make the corrected eye slightly hyperopic. Focus offset Do may be modified by a focus variation (ds) 66 that is determined from wavefront measurement 60.

[0049] Without the focus offset when the eye is refracted for a perfect focus at an acuity chart around 4 meters away, the eye will have a focus error of 0.25 Diopter when it sees distance objects. Therefore, the retinal contrast for distance vision will be reduced from high contrast (curve 54) to low contrast (curve 56 in FIG. 5). To make the eye see 20/10 or better for distance vision, the corrected eye must be set hyperopic in manifest refraction with an acuity chart around 4 meters away. Because the corrected eye can accommodate from infinity to a near distance, it will have superior vision outcomes for the entire range of eye's accommodation from far distance.

[0050] Finally, a refractive prescription for a customized lens 64 is generated by combining the objectively determined astigmatism Dc, the subjectively measured focus error Ds, and a focus offset Do. The focus offset can be set within the range of 0.075 D to 0.5 D.

[0051] Determining astigmatism of an eye from objective measurements of the eye's wave aberration may include the following steps: 1) measuring wave aberration of an eye using a device such as a wavefront aberrometer for a plurality of times, where wave aberration includes not only low-order aberrations such as a focus error and astigmatism but also high-order aberrations such as coma and spherical aberration, 2) deriving an optimized astigmatism for the eye for each of wavefront measurements, and 3) determining astigmatism of the eye by averaging the repeated measurements determined from plurality of times the eye's wave aberrations are measured.

[0052] A customized lens 65 can be fabricated to provide a customized refractive correction once a custom refractive prescription 64 is obtained. The customized lens can be configured as a spectacle lens or a contact lens. [0053] The improved method in FIG. 6 for customizing refractive lenses for an eye may be implemented through a wavefront-controlled system to avoid any human error in setting the desired focus offset, and enable all electronic transfer of refractive correction for improved simplicity and consistency.

[0054] The system of FIG. 6 in one embodiment comprises the following subsystems: a) A phoroptor module with a plurality of spherical lenses and cylindrical lenses, plus an acuity chart for subjectively determining a focus error and cylinder error of an eye and for previewing an astigmatism-free correction before a lens is made. The acuity chart has an optical distance to the eye around 4 meters, the same as in conventional clinical practice. The optical distance can be a physical distance or achieved with reflection of one or a plurality of mirrors. The spherical lenses of the phoroptor are set for subjectively optimizing vision and retina contrast of an eye for seeing the acuity chart, b) A wavefront sensor module for measuring wavefront slopes across pupil of an eye. The wavefront sensor module is configured to produce a light source on the retina of an eye as well as to convert to digital signals the reflected light across the eye's pupil from the retina, c) A digital processor connected to the wavefront sensor module for computing wave aberration of an eye from the converted digital signals from the wavefront sensor module. The digital processor is further configured to control the phoroptor module for the selection and orientation of cylinder lenses, d) An output module for generating a refraction prescription of at least a focus error and a cylinder error (power and angle) for a correction lens. The cylinder error is generated from the wavefront sensor module and digital processor, and the focus error is different from the combined power of the spherical lenses in the phoroptor module by an offset for improved retina contrast for distance vision.

[0055] In one embodiment, the offset between the focus error in the output module and the combined power of said spherical lenses in the phoroptor module relates to the optical distance of the acuity chart and the eye.

[0056] In another embodiment, the offset between the focus error in the output module and the combined power of the spherical lenses in the phoroptor module is around 0.25 Diopters.

[0057] While the specification has been described in detail with respect to specific embodiments of the invention, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention. Thus, it is intended that the present subject matter covers such modifications and variations.

Claims

What is claimed is:

1. A method for mitigating astigmatism of an eye, wherein the eye has a pupil, the method comprising the steps of:

a) measuring refractive errors of an eye, wherein the refractive errors comprise at least a focus error and a cylinder error;

b) determining a refractive prescription for a lens, wherein the refractive prescription comprises:

bl) a focus power that equals to or is approximated to the measured focus error; and b2) a spherical aberration coexisting with a focus offset that is distributed either in the central pupil with a diameter up to 4.5 mm or across the entire pupil of an eye, wherein the spherical aberration has an optical path difference expressed as a quadric term of the distance from the lens center (p⁴) and is induced into eye's optics for mitigating the measured cylinder error in an eye; and

c) fabricating an aspheric lens based on the determined refractive prescription for a refractive correction of an eye.

2. The method of claim 1 wherein the fabricated aspheric lens is a contact lens.

3. The method of claim 2 further comprising the step of fitting the eye with a test contact lens having known refractive properties before the step of measuring refractive errors of an eye, and wherein the determined refractive prescription further comprises a modification based on the known refractive properties of the test contact lens.

4. The method of claim 1 wherein the spherical aberration is determined based on the measured cylinder error in the eye.

5. The method of claim 1 wherein the spherical aberration generates an optical path difference in a range between 1 and 10 microns.

6. The method of claim 1 wherein the step of measuring refractive errors of an eye uses a wavefront system for measuring the cylinder error, and uses manifest refraction for measuring the focus error.

7. A wavefront system for customizing refractive corrections of an eye, wherein the eye has a retina and a pupil, wherein the system comprises:

a) a wavefront sensor module capable of measuring wavefront slopes across the pupil; wherein the wavefront sensor module is configured to produce a light source on the retina as well as to convert light which is reflected across the eye's pupil from the retina into digital signals;

b) a digital processor connected to the wavefront sensor module, wherein the digital processor is capable of computing wave aberration of an eye from the converted digital signals of the wavefront sensor module, and wherein the digital processor is further configured to provide simulated vision comparison between:

bl) a first refractive correction that includes focus error of the eye; and

b2) a second customized refractive correction that is represented by a focus power and an artificially induced spherical aberration coexisting with a focus offset that is distributed either in the central pupil with a diameter up to 4.5 mm or across the entire pupil of an eye; and

c) a display module capable of previewing simulated refractive outcomes of the second customized refractive correction in comparison to the first refractive correction.

8. The system of claim 7 further comprising a phoroptor module, wherein the phoroptor module obtains measurements of a focus error and a cylinder error of an eye subjectively.

9. The system of claim 7 wherein the previewing simulated refractive outcomes further comprises generating a refractive prescription for a customized lens.

10. The system of claim 9 further comprising an output module capable of displaying, printing, or transmitting a refractive correction.

11. The system of claim 7 wherein the simulated vision comprises (i) a determined residual aberration of an eye based on the computed wave aberration and the first and the second refractive correction separately; (ii) a computed image metrics that includes a simulated acuity chart and/or a retinal contrast distribution; and (iii) a display of the computed image metrics for previewing refractive outcomes.

12. A method for customizing a contact lens for an eye, the method comprising the steps of:

a) fitting an eye with a test contact lens, wherein the refractive power of the test contact lens is known and comprises a focus power and an optional cylinder power;

b) objectively determining astigmatism of the eye fitted with the test contact lens by measuring wavefront slopes of light from the retina of the eye, wherein the astigmatism is represented by a cylinder power and a cylinder angle;

c) subjectively determining a focus error of the eye at a far accommodation state using an acuity chart, wherein the acuity chart is set at an optical distance of between 3 meters and 15 meters; and

d) providing a refractive prescription by combining the known refractive properties of the test contact lens, the objectively determined astigmatism, the subjectively determined focus error of the eye, and an additional focus offset to improve retinal contrast for viewing distance beyond the acuity chart.

13. The method of claim 12 wherein the additional focus offset is around 0.25 Diopters so that the corrected eye will be slightly hyperopic.

14. The method of claim 12 wherein the test contact lens comprises an alignment mark.

15. The method of claim 12 wherein the step of objectively determining further comprises the steps of:

a) measuring wave aberration of the eye fitted with the tested contact lens for a plurality of times, wherein the wave aberration includes low-order aberrations such as a focus error and astigmatism and also includes high-order aberrations such as coma and spherical aberration;

b) deriving an optimized astigmatism for the eye for each wavefront measurement; and

c) determining astigmatism of the eye by averaging the plurality of measurements produced from the plurality of times.

16. The method of claim 12 wherein the refractive prescription further comprises an addition of a spherical aberration or a distribution of spherical aberration for a presbyopic treatment of the eye, wherein the spherical aberration is applied only in the central pupil of an eye.

17. The method of claim 12 further comprising the step of fabricating a toric contact lens based on the refractive prescription.

18. A method for prescribing refractive corrections of an eye for a human subject, the method comprising the steps of:

a) measuring optical properties of an eye, wherein the optical properties comprise: al) an objective measurement of the eye's wave aberration, wherein the objective measurement measures wavefront slopes across a pupil of the eye; and

a2) a subjective measurement of the eye's focus error using human response of an acuity chart;

b) specifying a refractive prescription for a customized lens, wherein the lens is one of:

bl) a customized aspheric lens, whose prescription is determined by the subjectively measured focus error, an artificially induced spherical aberration, and a focus offset that coexists with the induced spherical aberration for mitigating astigmatism in the eye that is not prescribed in the refractive correction; or

b2) a customized aspheric lens for the treatment of presbyopia, whose prescription is determined by the subjectively measured focus error, an astigmatism that is determined from the objectively measured wave aberration of an eye, and an artificially induced spherical aberration or a distribution of spherical aberrations only in the central pupil of an eye with a diameter less than 4.5 mm;

c) determining residual wave aberration of the eye based on measured optical properties of the eye and the generated refractive prescription for the customized lens;

d) computing at least one image metrics from the determined residual wave aberration of the eye, wherein the computed image metrics comprises simulated vision outcomes, wherein the simulated vision outcomes comprises a simulated acuity chart or a simulated retinal contrast distribution;

e) displaying the computed image metrics for previewing a customized prescription; and

f) providing a customized refractive prescription for a lens if the computed image metrics is considered acceptable.

19. The method of claim 18 wherein the step of measuring optical properties is performed in a clinical office and is submitted to a remote site where the lens is designed.

20. The method of claim 18 further comprising the step of transmitting the simulated vision outcomes from a remote site to a clinical office for previewing and/or selecting a customized lens.

21. The method of claim 18 further comprising the step of fitting the eye with a test contact lens having a known refractive power before said measuring optical properties of an eye, and wherein the customized refractive prescription further includes a modification based on the known refractive powers of the test contact lens.

22. The method of claim 18 further comprising the step of fabricating a lens according to the customized refractive prescription.

23. The method of claim 18 further comprising the step of modifying the customized refractive prescription, and wherein the step of displaying the computed image metrics includes simulated vision outcomes for a plurality of refractive prescriptions.

24. A method for customizing vision of an eye, the method comprising the steps of: a) objectively determining astigmatism of an eye by measuring the eye's wave aberration using a wavefront aberrometer, wherein the astigmatism is represented by a cylinder power and a cylinder axis, and wherein the cylinder power has a resolution finer than 0.25 Diopters (D);

b) subjectively determining a focus error of the eye at a far accommodation state using an acuity chart; c) determining a focus offset between 0.075 D and 0.5 D to improve retinal contrast for far vision; and

d) generating a refractive prescription for a customized lens by combining the objectively determined astigmatism, the subjectively determined focus error, and the determined focus offset for improved retinal contrast.

25. The method of claim 24 wherein the step of objectively determining astigmatism of an eye comprises the steps of:

a) measuring wave aberration for a plurality of times, wherein the wave aberration includes low-order aberrations such as a focus error and astigmatism and also high-order aberrations such as coma and spherical aberration;

c) determining astigmatism of the eye by averaging the repeated measurements of eye's astigmatism produced from the plurality of times.

26. The method of claim 24 wherein the acuity chart is set at an optical distance of between 3 meters and 15 meters.

27. The method of claim 24 wherein the determined focus offset is custom determined according to the variation of the eye's focus power in a plurality of repeated wavefront measurements.

28. The method of claim 24 further comprising the step of fabricating a customized lens based on the generated refractive prescription, wherein the customized lens is configured as a wearable or implantable lens.

29. A system for customizing refractive corrections of an eye, wherein the eye has a retina and a pupil, the system comprising:

a) a phoroptor module having a plurality of spherical lenses and cylindrical lenses, and having an acuity chart for subjectively determining a focus error of the eye, wherein the acuity chart has an optical distance to the eye around 4 meters, and wherein and the combined power of the spherical lenses are set for optimizing vision and retina contrast of an eye at the acuity chart;

b) a wavefront sensor module capable of measuring wavefront slopes across the pupil of the eye, wherein the wavefront sensor module is configured to produce a light source on the retina as well as to convert to digital signals from the reflected light across the eye's pupil from the retina;

c) a digital processor connected to the wavefront sensor module, wherein the digital processor is capable of computing wave aberration of the eye from the converted digital signals of the wavefront sensor module, and wherein the digital processor is further configured to control the phoroptor module for the selection and orientation of cylinder lenses; and

d) an output module for generating a refraction prescription of at least a focus error and a cylinder error (power and angle) for a correction lens, wherein the cylinder error is generated from the wavefront sensor module and the digital processor, and wherein the focus error is different from the combined power of the spherical lenses in the phoroptor module by an offset for improved retina contrast for distance vision.

30. The system of claim 29 wherein the offset between the focus error in the output module and the combined power of said spherical lenses in the phoroptor module relates to the optical distance of the acuity chart and the eye.

31. The system of claim 29 wherein the offset between the focus error in the output module and the combined power of said spherical lenses in the phoroptor module is

approximately 0.25 Diopters so that the corrected eye will be slightly hyperopic.