Method for designing, evaluating and optimizing ophthalmic lenses and laser vision correction

Abstract

The present invention relates generally to lens design and, more particularly, to a method for designing, evaluating and optimizing ophthalmic lenses and laser vision correction in order to optimally manage issues resulting from, or related to, halos.

Claims

1. A method comprising steps of: obtaining corneal aberration data by measuring corneal aberrations of a patient's eye having a halo and having a multifocal intraocular lens implanted therein; utilizing the corneal aberration data in a first eye model to calculate a simulated halo image, and wherein the first eye model is further comprised of a multifocal intraocular lens; providing a reference halo or a set of reference halos produced from a second eye model having the multifocal intraocular lens of the first eye model and having corneal aberrations that are different than the corneal aberrations of the patient's eye or having no corneal aberrations; comparing the simulated halo image to the reference halo or the set of reference halos; determining, based on the comparison of the simulated halo image to the reference halo or the set of reference halos, whether the halo results from the corneal aberrations of the patient's eye; and determining a laser vision correction to be applied to the patient to modify the corneal aberrations of the patient's eye to reduce the halo, the laser vision correction being determined based on the comparison of the simulated halo image to the reference halo or the set of reference halos.

2. The method of claim 1, wherein the reference halo or the set of reference halos demonstrate dysphotopsia.

3. The method of claim 1, wherein calculating the simulated halo image includes determining a halo size, a halo shape, and a halo intensity.

4. The method of claim 1, further comprising a step of applying the determined laser vision correction to the patient's eye.

5. The method of claim 1, further comprising utilizing an extended light source to calculate the simulated halo image.

6. The method of claim 5, wherein calculating the simulated halo image includes calculating a point spread function from the first eye model and convolving the point spread function with the extended light source.

7. The method of claim 1, wherein the first eye model is of the patient's eye.

8. The method of claim 1, further comprising a step of producing the reference halo or the set of reference halos.

9. The method of claim 1, wherein the step of determining the laser vision correction includes determining the laser vision correction that will minimize the halo.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Understanding of the disclosure will be facilitated by consideration of the following detailed description of the embodiments, taken in conjunction with the accompanying drawings, in which like numerals refer to like parts and in which:

(2) FIG. 1 is an illustration of an eye in the natural state;

(3) FIG. 2 is an illustration of an eye having an intraocular lens;

(4) FIG. 3 is a flow diagram illustrating a method for optimizing an ophthalmic lens in accordance with the present invention;

(5) FIG. 4 illustrates the halo image of 46 physiological eyes as further detailed below;

(6) FIG. 5 is a flow diagram illustrating a method for optimizing an ophthalmic lens in accordance with the present invention;

(7) FIGS. 6a and 6b are examples of halo size, shape and intensity in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purposes of clarity, many other elements found in typical optical and optical simulation apparatuses, systems and methods. Those of ordinary skill in the art will recognize that other elements are desirable and/or required in order to implement the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein.

(9) FIG. 1 is an illustration of an eye 10 in the natural state. The eye 10 includes a retina 12 for receiving an image, produced by the cornea 14 and the natural lens 16, from light incident upon the eye. The natural lens 16 is disposed within a capsular bag 20. The iris 26 separates the anterior and posterior chambers of the eye and may operate to change the aperture, i.e. pupil size of the eye. More specifically, the diameter of the incoming light beam is controlled by the iris 26, which forms the aperture stop of the eye.

(10) The capsular bag 20 is a resilient material that changes the shape and/or location of natural lens in response to ocular forces produced when the ciliary muscles 22 contract and stretch the natural lens 16 via the zonular fibers 24 disposed about an equatorial region of the capsular bag 20. This shape change may flatten the natural lens 16, thereby producing a relatively low optical power for providing distant vision in an emmetropic eye. To produce intermediate and/or near vision, the ciliary muscles 22 contract, thereby relieving tension on the zonular fibers 24. The resiliency of the capsular bag 16 thus provides an ocular force to reshape the natural lens 16 to modify the curvature to provide an optical power suitable for required vision. This change, or accommodation, is achieved by changing the shape of the crystalline lens. Accommodation, as used herein, includes changing the focus of the eye for different distances.

(11) FIG. 2 illustrates an eye 10 having a natural lens replaced with an IOL 102. The natural lens may require removal due to a refractive lens exchange, or due to a disease such as cataracts, for example. Once removed, the natural lens may be replaced by an IOL 102 to provide improved vision in the eye. The IOL 102 may include an optic and haptics 104 or support structure for centering the optic. The haptics 104 may center the optic, and may transfer ocular forces from the ciliary muscle 22, zonules 24, and/or capsular bag 20 to the optic to change the shape, power, and/or axial location of the optic relative to the retina 12.

(12) FIG. 3 is a flow diagram illustrating methods of optimizing an ophthalmic lens, such as, for example, the IOL illustrated in FIG. 2, in accordance with the present invention. In the illustrated method, an ophthalmic lens may be designed and/or provided for modeling and for clinical application. With reference to FIG. 3, a method of optimizing, evaluating and/or designing an ophthalmic lens is comprised of measuring the preoperative corneal aberrations of the patient according to well-known topographical measurement methods. This may be done by taking the difference in optical path between the chief ray and a marginal ray over the pupil which yields the wavefront aberration for the cornea. (Guirao, A., & Artal, P. (2000). Corneal wave aberration from videokeratography: accuracy and limitations of the procedure. J Opt Soc Am A, 17 (6), 955-965.). Alternatively, ray tracing can be performed, e.g. using general purpose optical design software (e.g. Code V, Zemax, OSLO).

(13) Preferably, at least the front corneal surface is measured and more preferably both the front and rear corneal surfaces are measured and characterized together in resulting wavefront aberration terms, such as a linear combination of polynomials which represent the total corneal wavefront aberrations. In the art of optics, topographical processes may include mathematically modeling a surface of the cornea using polynomial expansion series techniques, e.g. Seidel or Zernike polynomials, or the wavefront aberration can be calculated over a grid of points over the pupil.

(14) For normal healthy corneas, 5.sup.th order Zernike expansion is typically sufficient to describe the corneal aberrations. The aberrations include both lower order terms, such as defocus and astigmatism, along with higher order terms, such as spherical aberration, coma, trefoil, etc., up to pentafoil. However, for non-uniform corneas, like post-LASIK corneas, more terms may be needed. For non-uniform corneas, it may be necessary to describe the corneal aberrations at discrete points on a grid filling the pupil.

(15) The correlation between corneal aberrations and halo shape and intensity is demonstrated in the following example which encompasses the use of a set of 46 physiological eye models. The eye model (computer models) are based on the eyes of 46 cataract patients, and are described in further detail in the following which are incorporated herein by reference: Weeber, H. A., Featherstone, K. A., & Piers, P. A. (2010). Population-based visual acuity in the presence of defocus well predicted by classical theory. J. Biomedical Optics, 15 (4), 040509/040501-040509/040503; Weeber, H. A., & Piers, P. A. (2010). Optical and Visual Performance of Patient Populations Implanted With Monofocal and Multifocal IOLs in the Presence of Defocus. Invest. Ophthalmol. Vis. Sci., 51: E-Abstract 5751; Weeber, H. A., & Piers, P. A. (2011). Theoretical Performance of Intraocular Lenses correcting both Spherical and Chromatic Aberration. J. Refr. Surg., DOI: 10.3928/1081597X-20111103-01

(16) The corneas of these eye models are described by 5th order Zernike sag surfaces, and the eye models have spectacle lenses in front of them. For this analysis, the eye models were implanted with a diffractive multifocal IOL, having a pupil-independent diffractive profile across the entire optic, and a 50%:50% light distribution between far and near focus. However, it should be appreciated by those skilled in the art that any other multifocal lens would generate comparable analysis.

(17) In addition to the set of physiological eyes, diffraction limited eyes were generated having the same corneal power, but generating no wavefront aberrations. These eye models served as reference models, being perfect eyes.

(18) All eye models have a physical pupil diameter of 4 mm which represents the pupil diameter of an average cataract patient under mesopic lighting conditions.

(19) For both setsthe physiological eye models, and the corresponding diffraction limited eye modelspolychromatic point spread functions (PSF) were calculated.

(20) Then, an extended source, representing a headlight of 15 cm diameter at a 100 m distance was convoluted with the PSF. This resulted in the retinal image of the headlight, furtheron referenced as halo images. For optimal display and print, the pictures were processed using a gamma correction of 0.4. FIG. 4 shows the halo images of the 46 physiological eye which clearly demonstrates that the halo appearance differs considerably between the different eye models.

(21) An assessment of the patient inconvenience from halos can be done in a variety of ways. One way is to determine the retinal image of halos in patients, and then assess the nuisance perceived by these patients (e.g. by a questionnaire). Alternatively (and as done in this example), the patient inconvenience from halo images can be estimated by assessment of the shape, area, brightness and contrast of the halo images. There are two additional ways to assess the halo image: by evaluating the halo image of the physiological eye, and by evaluating the difference between the halo image of the physiological eye and that of the diffraction limited eye. In the latter case, the halo image of the diffraction limited eye is subtracted from the halo image of the physiological eye. The resulting image (delta image) highlights the halo only, without the central headlight.

(22) These aspects are consolidated in the following metrics for halo patient inconvenience and corneal aberrations, the correlation between which are illustrated in Tables 1 and 2 below:

(23) H1. (Image-)Correlation between the halo image of the physiological eye and the halo image of the diffraction limited eye. As the halo image of the diffraction limited is rotationally symmetric, with a uniform brightness of the halo, deviations denote changes in shape and brightness of the image.

(24) H2. Area of the halo image

(25) H3. Brightness of the halo image

(26) H4. Brightness of the delta image

(27) H5. RMS Contrast of the halo image

(28) H6. RMS Contrast of the delta image

(29) The optics of the cornea can be expressed in a variety of ways, including as follows:

(30) O1. Wavefront aberration: RMS of the higher order aberrations, based on the Zernike coefficients over a 4-mm pupil (HOA)

(31) O2. Wavefront aberration: RMS of the higher order aberrations, including the astigmatism terms, based on the Zernike coefficients over a 4-mm pupil (HOAA)

(32) O3. Wavefront aberration: RMS of the asymmetrical higher order aberrations, including the astigmatism terms, based on the Zernike coefficients over a 4-mm pupil (AHOAA)

(33) O4. Wavefront aberration: Coma, based on the Zernike coefficients over a 4-mm pupil (HOA)

(34) O5. Wavefront aberration: Astigmatism, based on the Zernike coefficients over a 4-mm pupil (HOA)

(35) O6. Wavefront aberration: Coma multiplied by Astigmatism, based on the Zernike coefficients over a 4-mm pupil (HOA)

(36) O7. MTF Volume

(37) O8. Area under the radial MTF curve

(38) It should be understood that metrics have been derived from the halo images, and many other metrics can be derived, as known by those skilled in the art. The central theme is that the metrics are based on a retinal image of an extended object. In this example, the extended object is the headlight of a car.

(39) Similarly, it should be understood that metrics have been derived from the optics of the eye, and many other metrics can be derived, as known by those skilled in the art. The central theme is that the metrics are based on the optics of the eye. In this example, the optics are described by corneal wavefront aberrations. The optics may further include aberrations caused by the internal optics of the eye, including those caused by the posterior cornea, and IOL misalignments.

(40) Tables 1 and 2 show the results of single variable linear regression between the metrics of the bother of halo images and the metrics of the optics of the eye. Table 1 shows the P-values of least squares linear regression between the H- and O metrics. Table 2 shows the regression coefficient R.sup.2. These results show that the patient inconvenience from halo images is significantly correlated with the optical characteristics of the eye.

(41) TABLE-US-00001 TABLE 1 H1 H2 H3 H4 H5 H6 O1 4E11 0.03 1E05 0.18 3E06 9E12 O2 4E09 4E03 1E07 0.27 3E08 2E12 O3 7E11 0.04 2E06 0.34 3E07 2E13 O4 1E15 0.86 2E02 0.24 4E03 4E10 O5 1E03 2E03 7E07 0.62 5E07 2E06 O6 2E11 0.02 4E07 0.34 3E08 2E15 O7 2E16 0.72 2E03 0.10 1E04 3E15 O8 3E17 0.18 6E06 0.02 2E07 5E21

(42) TABLE-US-00002 TABLE 2 H1 H2 H3 H4 H5 H6 O1 0.63 0.11 0.36 0.04 0.39 0.66 O2 0.55 0.17 0.48 0.03 0.51 0.68 O3 0.62 0.09 0.40 0.02 0.45 0.71 O4 0.77 0.00 0.11 0.03 0.17 0.59 O5 0.21 0.20 0.43 0.01 0.44 0.40 O6 0.64 0.11 0.45 0.02 0.51 0.77 O7 0.79 0.00 0.21 0.06 0.28 0.76 O8 0.81 0.04 0.38 0.12 0.46 0.87

(43) The above analysis demonstrates that the characteristics of the halo of multifocal IOLs are strongly influenced by ocular aberrations. In a preferred embodiment, the preoperative corneal aberrations of a patient are measured. If the pre-operative corneal aberrations exceed a certain threshold with respect to halo tolerance, then this can be a contraindication for implantation of a multifocal IOL.

(44) The corneal aberrations can also be used to determine the type of multifocal IOL to be implanted, for example an aberration inducing or correcting IOL. Optimization may include modifying the design of the ophthalmic lens to change the shape and intensity profile in order to minimize halo inconvenience as further discussed below. It may be that specific shapes/intensity of a halo are less disturbing than the symmetrical homogenous intensity halo of a schematic eye. The IOL design can be optimized for a group of patients, e.g. the general cataract population of for a specific patient as detailed further below.

(45) Additionally, the add power and light distribution for a diffractive multifocal IOL may be modified based on the corneal aberrations. For example, if a severe halo is expected based on corneal aberration analysis, then, in order to mitigate the inconvenience from halos, a multifocal IOL with a far-dominant light distribution may be chosen. For the same reason a multifocal IOL with a low add power may be chosen.

(46) With reference to FIG. 3, preferred embodiments include utilizing corneal aberration data (which may include metrics based on corneal aberrations) in a computer-based eye model wherein retinal images of extended light sources are simulated. This could be performed via ray tracing using general purpose optical design software (e.g. Code V, Zemax, OSLO). The corneal shape may be part of the model eye. A multifocal intraocular lens is then appropriately positioned in the model. From this model eye, the point spread function (PSF) is calculated for a point source at the chosen vision condition, e.g. for distance vision. Subsequently, the PSF is convolved with an extended light source. Typically, the extended light source represents the headlight of a car. The convolved image represents a retinal light intensity profile of the extended light source, and reveals the size, shape and intensity of the halo.

(47) This profile may then be compared to a reference halo, or set of reference halos, which demonstrates an acceptable dysphotopsia profile. The reference halos may be created by any of the following ways: by comparing the simulated halos from a group of multifocal IOL patients with their reported discomfort caused by halos; by displaying simulated images to a reference group and ranking the images based on expected discomfort; by measuring optical and visual performance of a reference group of multifocal IOL patients; or by having a reference group participate in a vision simulator experiment, in which the aberrations in the patient's eye are varied, while the visual performance is being tested. Once a (set of) reference halo(s) is created, the simulated halo may be compared to the reference halo. Based on this comparison, a decision may be made whether or not to (1) implant the multifocal IOL, (2) choose which IOL design to implant, (3) further optimize an IOL design, and/or (4) in the case of laser treatment decide on the treatment profile. In any case, the comparison between the simulated halo and reference halo optimizes the treatment in terms of mitigating the bother from halos.

(48) FIG. 5 is a flow diagram illustrating another preferred embodiment wherein the preoperative corneal aberrations of a patient are measured and then simulated halo images calculated for these aberrations, with the multifocal IOL. The halo size, shape and intensity of the simulated images are then compared to a reference halo demonstrating acceptable dysphotopsia. Based on this information, the IOL aberration profile can be tailored so as to result in reduced or minimal bother from halo, specifically when combined with the patient's corneal aberration profile. For example, if the corneal aberrations include large amounts of coma and trefoil that produce a large and intense halo, an IOL could be designed that compensates for the corneal coma and trefoil, and thus, reduces or minimizes the halo. In comparison, spherical aberration has little effect on the halo appearance. This means that spherical aberration can be corrected or induced without (much) consequences for the bother from halos.

(49) When the optical aberrations of the eye are expressed in terms of MTF Volume or area under the MTF curve, the correlation between halo appearance appears very strong. As the MTF Volume or the area under the MTF curve increases, less bother from halo is expected.

(50) Clinically, it may happen that (for some patient or group of patients) a homogeneous and circular halo is not the optimal shape. In that case, the desired halo is not the halo as obtained with an aberration free eye, as used in the above example. However, the desired halo can be obtained by designing an IOL that introduces asymmetrical aberrations, such as coma, in order to match the desired halo.

(51) In another preferred method an optimal aberration is determined using a vision simulator. The patient's natural aberrations are compensated by the instrument and a predetermined set of aberrations is induced. The patient looks at a scene, e.g. a night-driving scene, or a scene street lights, and then several sets of predetermined aberrations may be compared. The patient can then select the best scene (least disturbing halos). Alternatively, the patient can manipulate the magnitude and type of aberrations manually. Or, a set of sample images may be presented to the patient which represent the simulated scenes with different halo types. The patient can then select the best scene, and the appropriate IOL may be implanted or optimized and then implanted.

(52) Laser ablation procedures can remove a targeted amount stroma of a cornea to change a cornea's contour and adjust for aberrations. In known systems, a laser beam often comprises a series of discrete pulses of laser light energy, with a total shape and amount of tissue removed being determined by a shape, size, location, and/or number of laser energy pulses impinging on a cornea.

(53) In a specific example, the corneal topography of a multifocal IOL patient was measured, and the corneal aberrations are calculated, as described above. The corneal aberrations, for a 6-mm corneal aperture are listed in table 3. The Zernike terms listed are shown in micrometers. A computer model of the patient's eye was made, and a multifocal lens inserted into the model eye. Using ray tracing, a PSF was calculated from the eye model, and the PSF was convolved with an extended light source. The result was a simulated halo, as shown in FIG. 6A. The size of this halo may be influenced by adjusting the corneal aberrations using laser vision correction.

(54) As an example, the same calculation was carried out using corneal aberrations as shown in table 4. Again, a computer model of the eye was made, now having the adjusted corneal aberrations, and the multifocal intraocular lens. The PSF was calculated, and the PSF was convolved with an extended light source. This resulted in a simulated halo, as shown in FIG. 6B. This example shows that the size, shape, and light intensities of the halo are influenced by the corneal aberrations. A corneal laser vision correction may then be used to change the corneal aberrations listed in table 3, into those listed in table 4.

(55) TABLE-US-00003 TABLE 3 Zernike term Value Z0 1.19900 Z1 0.00700 Z2 0.00550 Z3 0.00058 Z4 0.38743 Z5 0.60012 Z6 0.84004 Z7 0.36840 Z8 0.50803 Z9 0.63816 Z10 0.09440 Z11 0.08633 Z12 0.17582 Z13 0.01241 Z14 0.00520 Z15 0.02003 Z16 0.28460 Z17 0.00506

(56) TABLE-US-00004 TABLE 4 Zernike term Value Z0 0.87200 Z1 0.03200 Z2 0.02350 Z3 0.03868 Z4 0.40131 Z5 0.01388 Z6 0.36911 Z7 0.32138 Z8 0.42977 Z9 0.11208 Z10 0.20435 Z11 0.14736 Z12 0.00632 Z13 0.00173 Z14 0.00115 Z15 0.00756 Z16 0.22073 Z17 0.03131

(57) Thus, a preferred embodiment, involves the following steps: measuring the preoperative corneal aberrations of the multifocal IOL patient; calculating a simulated halo image for these aberrations, with the multifocal IOL; determining the halo size, shape and intensity; having a reference halo which demonstrates acceptable dysphotopsia; optimizing the laser vision correction in order to achieve a minimal halo; applying the laser vision correction to the patient's cornea.

(58) Another preferred embodiment, involves: measuring the preoperative corneal aberrations of the multifocal IOL patient; using a vision simulator to measure the patient's visual performance (e.g. halo size, shape and intensity; discomfort, contrast vision, visual acuity), while varying the patient's corneal aberration; based on the test, determining the optimal corneal aberration as to optimize the visual performance; applying a laser vision correction to generate the optimal corneal aberration onto the patient's cornea.

(59) In another preferred method, after a multifocal IOL is implanted, one may measure corneal aberrations, e.g. by mathematically characterizing the corneal aberrations of the patient, using a method described above. Then a simulated halo image for these aberrations with the multifocal IOL may be calculated in order to determine the halo size, shape and intensity, as detailed previously. This simulated halo may then be compared to a reference halo which demonstrates acceptable dysphotopsia. If the simulated halo is significantly worse than the reference halo, the halo is predominantly caused by the corneal aberrations. Alternatively, a determination of whether the halo inconvenience results from corneal aberrations or the multifocal IOL may be based on experience of the relationship between patient complaints and ocular aberrations. This may be achieved by gathering information from patient files, and correlating the corneal data (corneal wavefront aberrations, calculated from corneal topography), with patient complaints referring to halos.

(60) Minimizing halos may then be achieved by modifying the ocular aberrations through laser vision correction, with the optimal aberrations for the patient being determined using a vision simulator of sample images, or as otherwise detailed herein. Alternatively, an adjustable IOL may be implanted and then the aberrations changed after implantation. Or, an add-on (piggyback) IOL may be placed in front of the multifocal IOL. It is also envisioned that the multifocal IOL can be exchanged with a more appropriate design, or a corneal implant may be used and then the aberrations changed after the corneal implant is in place.

(61) Another preferred embodiment, involves the following steps: optimizing a corneal correction (e.g. presby-lasik), the simulated halo image being one of the optimization parameters; applying the presby-laser vision correction to the patient's cornea. Prior to optimizing a corneal correction, one may measure the corneal aberrations of a patient suffering discomfort or reduced visual performance. It is envisioned that either the aberration profile can be optimized such that the halo will have minimal visual disturbances, or the aberration profile can be optimized such that the risk of severe visual disturbances is minimized.

(62) An exemplary ophthalmic lens would include an anterior surface and an opposing posterior surface wherein at least one of the surfaces of the ophthalmic lens is characterized by an equation including a first coefficient configured to compensate for a corneal aberration in order to shape the halo and intensity profile in order to minimize bother from the halo.

(63) Although the invention has been described and pictured in an exemplary form with a certain degree of particularity, it is understood that the present disclosure of the exemplary form has been made by way of example, and that numerous changes in the details of construction and combination and arrangement of parts and steps may be made without departing from the spirit and scope of the invention.