INTRAOCULAR LENS DESIGNS FOR OPTIMAL CLINICAL OUTCOME

CROSS-REFERENCE TO RELATED APPLICATIONS

[1] This application claims priority from the U.S. Provisional Patent Application No.

62/872,008 filed on July 9, 2019. The entire disclosure of the prior application is considered to be part of the disclosure of the accompanying application and is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[2] This disclosure generally relates to a design of intraocular lenses that reduce the adverse impact on the clinical performance of the lens related to surgical induced misalignment of lens resulting in decentration and/or tilt and the variation of spherical aberration on the corneas in the patient population, and more particularly to an intraocular lens having an aspherical profile and exhibiting a certain amount of spherical aberration and a certain range of shape factors.

2. Description of the Related Art

[3] Sir Nicholas Ridley is considered the father of intraocular lenses performing the first implant of an intraocular lens (IOL) in 1949. Although complications required the removal of the IOL, subsequent surgeries the following year were successful with the implanted IOL remaining permanently in the eye. Ridley continued his work and during the 1960s achieved a very high degree of success in the implantation of IOLs in humans. Cataract extraction surgery with intraocular lens implantation is now the most common type of eye surgery. The success of

IOL implant surgery has resulted in the rise of more sophisticated surgical procedures and increasingly more complex IOL designs that have improved the quality of the lives of many.

However, problems remain with IOL implant surgery with one of these problems being the misalignment in the form of decentration and tilt of the IOL following an implant. Symptoms of misaligned IOLs may range from light ghosting of objects and double vision to astigmatism.

Clinically, the affect of IOL misalignment can be measured with visual acuity (VA) and contrast sensitivity (CS).

[4] Decentration occurs when the optical axis of the IOL is shifted from the visual axis of the eye so that the visual axis of the eye and the optical axis of the IOL are parallel to each other but at some offset. Decentration of an IOL may be the result of surgical placement of the lens, or it may develop in the postoperative period because of external (e.g. trauma, eye rubbing) or internal forces such as scarring or capsular contraction. FIG. 1 A shows schematically IOL 10 properly positioned posteriorly to cornea 12 in the eye so that visual axis 14 of the eye and optical axis 16 of IOL 10 are congruent with one another. FIG. 1B shows the decentration of

IOL 10 in that optical axis 16 is offset from visual axis 14 by some distance 18.

[5] Lens tilt is defined as the angle between the IOL’s optical axis and the visual axis of the eye. Tilt of an IOL may be the result of inaccurate IOL surgical positioning, lack of capsular support, scleral tunnel positioning, and more. Tilt is shown in FIG. 1C where optical axis 16 of

IOL 10 is at some angular offset 20 from the eye’s visual axis 14.

[6] IOL decentration of greater than 1 mm or a tilt of greater than 5 degrees noticeably decreases VA and CS. Additionally, multifocal or toric IOLs exacerbate the effects of decentration or tilt so that decentration of less than 1 mm or a tilt of less than 5 degrees may adversely impact VA and CS. Although proper placement of the IOL within the capsular bag has become more commonplace as surgery techniques have improved, decentration and/or tilt may still occur even after an uneventful surgery. Therefore, it is important to decrease the amount of decentration and/or tilt of an implanted IOL by not only the utilization of improved surgical techniques but also by incorporating certain design features into the IOL so that the clinical performance of the IOL is insensitive to decentration and/or tilt as disclosed herein.

[7] Spherical aberration naturally exists on the human cornea with a population mean of

~0.28 mm. Through the aspheric design of the IOL, a negative spherical aberration can be created on the IOL to counter this corneal aberration so that patients using an IOL may have vision with little to no spherical aberration.

[8] U.S. Pat. No. 5,336,262 to Chu disclosed an intraocular lens suitable for scleral fixation having a disk-shaped lens optic with two flexible haptics projecting outwardly from opposite points on the lens optic's periphery. Each haptic includes one or more suture holes for use in suturing the haptic to the ciliary sulcus of an eye during implantation surgery. The suture holes are positioned such that they are located substantially at the haptic apexes when the lens is implanted, and the haptics have been flexed inwardly a predetermined amount. According to

Chu, this configuration minimizes the possibility of lens tilting and decentration. However, the presence of a suture increases the length of and complications during the surgery. Long-term monitoring of patients with sutured IOLs has identified certain suture-related complications, such as scleral and conjunctival erosion, suture-induced inflammation, suture degradation, and late luxation or subluxation of the IOL after suture rupture. It would be preferred to attenuate the problem of decentration and tilt by use of a sutureless IOL.

[9] U.S. Pat. No. 7,381,221 to Lang and et al discloses a multi-zonal monofocal IOL that comprises an inner zone, an intermediate zone, and an outer zone. The inner zone has a first optical power. The intermediate zone surrounds the inner zone and has a second optical power that is different from the first power by a magnitude that is less than at least about 0.75 Diopter.

The outer zone surrounds the intermediate zone and has a third optical power different from the second optical power. Lang states that the intermediate zone may also provide correction in cases of decentralization or tilting of the lens when the intermediate zone has a correction power that is less than the correction power of the inner zone. The Lang lens may have inherent tolerances against decentration or tilt, however, conceptually it is not a monofocal lens.

[10] What is needed is a sutureless IOL design that offers optimal clinical outcome with the optimized design of its shape factor and spherical aberration.

BRIEF SUMMARY OF THE INVENTION

[11] A series of monofocal or the spherical equivalent base curve of multifocal, toric, or extended depth of focus IOL having an optical power for implantation in an eye having a cornea, comprising: an anterior surface having an anterior radius; and a posterior surface having a posterior radius where one of the surfaces is aspherical; wherein the anterior radius and the posterior radius, along with the refractive index of the lens material, determine the optical power; and wherein the anterior radius and the posterior radius determine a shape factor of the lens that is negative and selected to minimize the adverse effects of decentration and/or tilt of the lens.

[12] An embodiment of the prior lens having a surface wherein any number of combinations of shape factor, conic constant, and/or aspheric coefficients may be modified to produce a certain spherical aberration that when combined with the spherical aberration of the cornea minimizes the overall ocular spherical aberration of the cornea and the IOL system. [13] Another embodiment is series of IOLs from low to high powers with a shape factor in the range from -0.45 to -0.8. The variable shape factor in the power series allow for sharing of the radius of curvature for one of the two surfaces of the lens. The embodiment shows the sharing of the radius of anterior surface curvature amongst a few adjacent diopters. This sharing strategy can be used for reducing the engineering complexity in manufacturing of the lenses

[14] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

[15] Neither this summary nor the following detailed description defines or limits the invention. The invention is defined by the claims.

BRIEF DESCRIPTION OF DRAWINGS

[16] The present invention will become more fully understood from the detailed description and accompanying drawings, wherein:

[17] FIG. 1 A shows a schematic of a properly positioned IOL within the eye showing the cornea of the eye wherein the optical axis of the IOL is congruent with the visual axis of the eye.

[18] FIG. 1B shows a schematic of a decentralized IOL within the eye showing the cornea of the eye wherein the optical axis of the IOL is parallel with the visual axis of the eye.

[19] FIG. 1C shows a schematic of a tilted IOL within the eye showing the cornea of the eye wherein the optical axis of the IOL is at some angular offset with the visual axis of the eye.

[20] FIG. 2 shows a chart depicting the relationship between the Zernike Standard

Coefficient Z ₁₁ of the spherical aberration type in relation to the shape factor of an IOL. [21] FIG. 3 A shows a chart depicting the relationship between the Zernike Standard

Coefficient Z ₁₁ and shape factor for an IOL with an optical power of 10 diopters.

[22] FIG. 3B shows a chart depicting the relationship between the Zernike Standard

Coefficient Z ₁₁ and shape factor for an IOL with an optical power of 20 diopters.

[23] FIG. 3C shows a chart depicting the relationship between the Zernike Standard

Coefficient Z ₁₁ and shape factor for an IOL with an optical power of 30 diopters.

[24] FIG. 4 shows graphs depicting the performance of aspheric designs of a mid-power IOL in terms of MTF with a spherical aberration of 0.0 mm at 3 mm aperture for ISO model eye 2.

[25] FIG. 5 shows graphs depicting the performance of aspheric designs of a mid-power IOL in terms of MTF with a spherical aberration of -0.14 mm at 3 mm aperture for ISO model eye 2.

[26] FIG. 6 shows graphs depicting the performance of aspheric designs of a mid-power IOL in terms of MTF with a spherical aberration of -0.28 mm at 3 mm aperture for ISO model eye 2.

[27] FIG. 7 shows graphs depicting the performance of aspheric designs of a mid-power IOL in terms of MTF with a spherical aberration of 0.0 mm at 5 mm aperture for ISO model eye 2.

[28] FIG. 8 shows graphs depicting the performance of aspheric designs of a mid-power IOL in terms of MTF with a spherical aberration of -0.14 mm at 5 mm aperture for ISO model eye 2.

[29] FIG. 9 shows graphs depicting the performance of aspheric designs of a mid-power IOL in terms of MTF with a spherical aberration of -0.28 mm at 5 mm aperture for ISO model eye 2.

[30] FIG. 10 shows a table containing the relevant lens parameters for the first embodiment of an IOL power series having an aspherical anterior lens and a spherical posterior lens where R _a and R _p yields a shape factor of -1.5 and a spherical aberration value of -0.19 mm.

[31] FIG. 11 shows a table containing the relevant lens parameters for the second

embodiment of an IOL power series having a spherical anterior lens and an aspherical posterior lens where R _a and R _p yields a shape factor between -0.45 to -0.75 and a spherical aberration value of -0.12 mm.

DETAILED DESCRIPTION OF THE INVENTION

[32] It is to be understood that the figures and descriptions provided herein may have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, other elements found in typical vision correcting lenses, lens systems, and methods. Those of ordinary skill in the art may recognize that other elements and/or steps may be desirable and/or necessary to implement the devices, systems, and methods described herein. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps may not be provided herein. The present disclosure is deemed to inherently include all such elements, variations, and modifications to the disclosed elements and methods that would be known to those of ordinary skill in the pertinent art.

[33] The present invention encompasses a series of IOL designs that reduces sensitivity to variations of spherical aberration existent on the cornea of the patient and clinical decentration and tilt of the IOL; as described in FIGs 1A, IB, and 1C; as measured by the Modulus Transfer

Function (MTF) performance also known as the Modulus of the OTF (Optical Transfer

Function). MTF is a measure of visual performance that can be plotted vertically on a non- dimensional scale ranging from a minimum of 0.0 to a maximum of 1.0 against a horizontal range of a dimensional attribute. As MTF approaches 1.0 so will the VA or CS of the optical system improve. Conversely, as MTF approaches 0.0, so will the VA or CS of the optical system decrease. Theoretically, the MTF of any optical system including the human eye, can never reach to 1.0 at any spatial frequency other than 0. In this disclosure MTF will be plotted vertically against an attribute referred to as“focus shift” in millimeters. Focus shift represents the distance between the desired focus point in the eye, which is the retina, and the actual focal point. A negative focus shift indicates a focal point that is in front of the retina while a positive focus shift indicates a focal point that is behind the retina. In an emmetropic eye the focus shift will be zero, that is the image being formed on the retina, resulting in excellent VA and CS. As the focal point of the image moves further from the retina, the MTF decreases indicating that VA or CS has been degraded. The lens system in the eye for this disclosure comprises the cornea and the IOL and is also known as the pseudophakic eye. However, the principles disclosed herein may also be applied to a lens system for the eye that comprises the cornea, IOL, and the crystalline lens which is known as the phakic eye.

[34] The IOL design that reduces sensitivity to decentration and tilt of the IOL is based on the shape factor of the IOL base lens. An IOL consists of a circular disk portion, being a lens, usually having two or more side struts, called haptics, extending therefrom. The haptics hold the disk portion within the capsular bag of the eye. The IOL deflects light by both the structure of the disk and the structure of any surface effect on the anterior or posterior surface of the circular disk. For the purpose of this disclosure the base lens is the lens defined by the structure of the disk and expressed as shape factor. Shape factor is dimensionless and is determined by the radii of the anterior and posterior curvature of the lens by the following formula according to ISO-

11878:1 Where R _a and R _p are the anterior and posterior radius of curvature of the lens, respectively. The shape factor of a lens may also be defined with

Where C _a and C _p are the anterior and posterior curvature of the lens, respectively. Finally, it can be approved that

[35] In this disclosure, shape factor will be defined as shown in Eq. 1.

[36] It is well-known that the spherical aberration of a sphere single lens is affected by the shape factor of the lens. FIG. 2 shows the relationship between Zernike Standard Coefficient Z ₁₁ of the spherical aberration type in waves and the shape factor of an IOL. The IOL of FIG. 2 being of an average power, 20 D to be specific, and made from an n = 1.55 lens material and having a medium of n = 1.336. The results shown in FIG. 2 indicates that an IOL with an increasingly negative shape factor produce an increasingly positive Zernike spherical aberration.

Conversely, an IOL with an increasingly positive shape factor produces an increasingly negative Zernike spherical aberration. The sign of the shape factor is in line with the definition in Eq. (1).

The sign of the wavefront aberration also agrees with Zemax® wavefront sign convention.

Zemax® markets a family of optical system design software that may be used to model and simulate lens systems in the human eye. Their software is used in the analysis that follows. [37] The cornea is the first lens element of the human eye and generally has a positive spherical aberration from the fact that the human cornea has a prolate shape that produces a negative comeal Q value. In FIG. 2 it was shown that lenses with a positive shape factor inherently has a negative spherical aberration. Therefore, it becomes natural that IOLs with a certain positive shape factor will be able to compensate for the positive spherical aberration existing on the human cornea. IOLs with this positive shape factor will possess the“best form” for overall spherical aberration reduction in the aphakic eye. Prior art, such as U.S. Patent

Publication 2006/0227286 to Xin Hong titled“Optimal IOL shape factors for human eyes”, takes advantage of the characteristics of lenses with a positive shape factor for spherical aberration reduction. However, this invention is not going to take this advantage of the lens shape factor for spherical aberration reduction. Rather it is optimized for the optimal clinical outcome of the

IOL product.

[38] Another factor to consider is the effect of dioptric power and shape factor on spherical aberration present in an IOL. FIG. 2 shows the effect of a lens’ shape factor on spherical aberration lens as discussed earlier. However, a lens’ dioptric power also has an effect on spherical aberration along with the variation of lens shape factor. FIGs 3 A, B, and C shows that

IOLs with a lower dioptric power will exhibit a lower Z ₁₁ absolute spherical aberration than

IOLs of a higher dioptric power. These figures show, for a given IOL diopter, the relationship between the IOL’s shape factor and Z ₁₁ at a 6 mm aperture with the solid line showing Z ₁₁ expressed in wave and the dashed line showing Z ₁₁ expressed in micron for a shape factor in the range of -2.0 to 2.0. FIG. 3A shows that the absolute value for Z ₁₁ at an aperture of 6 mm in waves for an IOL of 10 diopters that ranges from zero to roughly 0.025 while FIG. 3C shows a range of zero to roughly 0.5 for an IOL of 30 diopters. FIG. 3B shows an absolute value for Z ₁₁ at an aperture of 6 mm in waves for an IOL of 20 diopters that ranges from zero to roughly 0.17.

Therefore, for the same spherical aberration correction, different shape factors and/or aspheric parameters for each lens might be employed in the lens power series design.

[39] FIGs 4 through 9 shows varying simulations in the form of charts to demonstrate the performance of IOL with various shape factors under three conditions: On- Axis where the IOL is properly positioned witting the capsular bag, 1.0 mm Decentered where decentration 20 in FIG.

IB is one millimeter, and 5° Tilted where tilt angle 22 shown in FIG. 1C is five degrees. For each of the three conditions, nine simulations were run for the following shape factors: -2.0, -1.5,

-1.0, -0.5, 0, 0.5, 1.0, 1.5, and 2.0. All total each of figures 4 through 9 contains 27 charts representing 27 simulations. The y-axis for each chart ranges from 0.0 to 1.0 and represents the

MTF determined by the simulation. As discussed earlier, as MTF approaches 1.0 VA and CS is improved and as MTF approaches zero VA and CS is degraded. The x-axis for each chart ranges from -0.3 mm to 0.3 mm and represents the focal shift from zero, or the retina. The four lines in each of the charts are defined as follows:

[40] The solid line shows the results of the simulation in the sagittal plane at a resolution of 50 lp/mm.

[41] The dash dotted line shows the results of the simulation in the sagittal plane at a resolution of 100 lp/mm.

[42] The dashed line shows the results of the simulation in the tangential plane at a

resolution of 50 lp/mm.

[43] The dotted line shows the results of the simulation in the tangential plane at a

resolution of 100 lp/mm.

[44] Resolution is defined by the frequency measured in line pairs per millimeter (lp/mm). The greater the number of line pairs per millimeter the more difficult it is for the eye to resolve the line pair thus MTF is reduced. When an IOL has been properly positioned in the capsular bag, as depicted by the On-Axis condition, tangential and sagittal perform the same thus the On-

Axis column of simulations only shows the solid line for MTF performance at 50 lp/mm and the dash dotted line for MTF performance at 100 lp/mm.

[45] FIG. 4 shows simulations of the three conditions as to various shape factors for an aspheric mid-power IOL at 3 mm aperture and a spherical aberration of 0.0 mm. FIG. 5 is similar to FIG. 4 but for a spherical aberration of -0.14 mm. FIG. 6 is similar to FIG. 4 but for a spherical aberration of -0.28 mm. FIG. 7 shows simulations of the three conditions as to various shape factors for an aspheric mid-power IOL at 5 mm aperture and a spherical aberration of 0.0 mm. FIG. 8 is similar to FIG. 7 but for a spherical aberration of -0.14 mm. FIG. 9 is similar to

FIG. 7 but for a spherical aberration of -0.28 mm. All simulations were performed using an ISO model eye 2 with spherical aberration matching that of the IOL.

[46] It is shown, through the many simulations in FIGs. 4 through 9, that MTF performance is degraded as shape factor is increased. This is particularly noticeable when comparing MTF performance at a shape factor of -2.0 to MTF performance at a shape factor of 2.0. Therefore, the simulation results, as depicted in figures 4 to 9, indicate that IOLs with a negative shape factor exhibit better resistance to lens misalignment of decentration and tilt than IOLs with a positive shape factor. However, as discussed earlier, IOLs with a negative shape factor are not able to compensate for the positive spherical aberration existing on the human cornea as shown in FIGs. 2 and 3. There are other attributes of an IOL that will alter the IOL’s spherical aberration without altering its shape factor primarily through the employment of aspheric designs including conic constant and aspheric parameters of a lens surface. The following even asphere equation is a general form that describes the sag of a lens surface which is effective in spherical aberration correction.

Where r is the radius of the lens aperture, c is the coverture of the lens surface, k is the conic constant, and a _i is the aspheric coefficient. Thus, there exist numerus combinations of shape factor, conic constant, and aspheric coefficients for IOL optical designs to achieve spherical aberration reduction. Therefore, aspheric intraocular lenses with negative shape factors can be designed to achieve both spherical aberration reduction and performance stability with mild/reasonable clinical misalignment.

[47] With Eq. 4 it is possible to realize a variety of different IOL designs having a common shape factor but with different dioptric power, anterior and posterior radius of curvature of the

IOL, or aspheric coefficients. Both shape factor and aspheric parameters can be optimized for optimal clinical outcome.

[48] FIG. 10 shows a first embodiment being a family of lenses where the anterior surface is aspherical and the posterior surface is spherical for a 5 mm model eye where the spherical aberration of the IOL offsets the spherical aberration of the cornea. The aspheric coefficients A ₄ ,

A ₆ , and A ₈ are determined so that each lens in this family of lenses will have a shape factor of -

1.5 and a spherical aberration of -0.19 mm. MTF25 shows the MTF value at focus with zero decentration and zero tilt at 25 lp/mm. MTF50 shows the MTF value at focus with zero decentration and zero tilt at 50 lp/mm. MTF 100 shows the MTF value at focus with zero decentration and zero tilt at 100 lp/mm. The refractive index of the lens material is n=1.483.

[49] FIG. 11 shows a second embodiment being a family of lenses where the anterior surface is spherical and the posterior surface is aspherical for a 5 mm model eye where the spherical aberration of the IOL offsets the spherical aberration of the cornea. The aspheric coefficients A ₄ and A ₆ are determined so that each lens in this family of lenses will have a shape factor in the range of -0.75 to -0.45 with a spherical aberration of -0.12 mm. MTF25 shows the MTF value at focus with zero decentration and zero tilt at 25 lp/mm. MTF50 shows the MTF value at focus with zero decentration and zero tilt at 50 lp/mm. MTF 100 shows the MTF value at focus with zero decentration and zero tilt at 100 lp/mm. The refractive index of the lens material is n=1.483.