FOLDABLE THIN INTRAOCULAR MEMBRANE

Abstract: A thin foldable intraocular implant (1) specifically configured for installation into the anterior chamber (10) of a phakic or pseudophakic eye has broad positioning flaps (8) that do not apply any substantial pressure against the wall of the eye. It can be rolled for insertion through a corneal incision as small as 2.75 millimeters. The implant is constituted by a resiliently flexible membrane, with an overall thickness not exceeding 125 microns, that vaults the iris without contacting it. In a first embodiment (3) of the invention, the optic is constituted by a refractive Fresnel-type pattern. An alternate embodiment features a multi-order diffractive (MOD) structure (101).

Description: PO DABLE THIN INTRAOCULAR MEMBRANE SPECIFICATION Field of the Invention The present invention relates to intraocular implants, and more specifically to implants intended to be inserted in the anterior chamber of the eye in order to correct optical deficiencies without removal of the crystalline lens. Background of the Invention Intraocular lenses (IOLs) are routinely used nowadays for restoring vision after removal of the cataracted lens. Whether the IOL is installed in the posterior chamber of the eye in lieu of the removed cataracted lens, or in the anterior chamber, it must be small enough to pass through a minimal corneal incision. The reduction in the overall dimension of the IOL is limited, however, by the necessity of avoiding glare by providing a substitute optic that is large enough to cover the pupil when it is fully dilated for proper night time vision. One approach to reducing glare while at the same time reducing the size of the incision in the cornea is to construct the IOL from several pieces which are joined together after the individual pieces are inserted through the corneal incision as disclosed in U.S. Patent No. 5,769,889 Kelman. The complexity of this type of IOLs, the difficulty of their post insertion assembly coupled with the required thickness and rigidity of the optic element, still force the ophthalmic surgeon into tolerable compromises between reduced size and peripheral glare coupled with impaired night vision. Conventional lenticular elements, whatever their size, are still subject to various spherical and thickness aberrations which are not easily correctable during the manufacture of the IOL. The invention results from a search for a simple, preferably one-piece IOL with an optic having a diameter sufficient to cover the size of a dilated pupil, but yet insertable to a relatively small corneal incision. Summary of the Invention The principal and secondary objects of this invention are to provide the ophthalmic surgeon with a simple, one-piece IOL which avoids the major drawbacks of the device of the prior art, particularly reduced coma, glare, impaired night vision, and blurring due to spherical and thickness aberrations, and which can be collapsed to a relatively small size for insertion through a corneal incision of about 2.75 millimeters. These and other valuable objects are achieved by forming a thin lens inherently immune to spherical and thickness aberrations on a resiliently flexible membrane that can be rolled or folded to pass through a small corneal incision. The thin lens optic typically uses a small central lenticular zone surrounded by a plurality of . optic rings concentric with the central zone and extends up to a total diameter of approximately 6 millimeters . In a first embodiment of the invention, the lenticular zone forms a refractive Fresnel-type lens. An alternate embodiment of the invention features a difractive phase Fresnel-type lens formed of concentric zones having profiles that provide a phase jump delay at each zone boundary which is a multiple of waves at the design wavelength in order to focus a plurality of different wavelengths to a single point. The membrane and its incorporated thin lens optic is arcuately shaped for installation in the anterior chamber where it vaults the iris and is stabilized by sets of obliques flaps that nest into the corner of the chamber. Contrary to the compressed haptics commonly used to secure prior art, IOLs, the aforesaid flaps do not exert any pressure upon the wall of the eye. The vaulted shape of the device combined with its thinness keep it away from the endothelium. Its neutral buoyancy prevents any pressure on the iris eliminating risks of closure, cataract or iris pigment dispersion. The large footprint of the flaps prevent synechiae and their encapsulation by the iris. The natural buoyancy of the device is improved by a plurality of fenestrations . The thin lens can be configured in a variety of successive dioptic powers, over a range from -15 to +15 diopters, in order to correct practically all types of refractive errors. Brief Description of the Drawing Figure 1 is a front elevational view of the preferred embodiment of the invention; Figure 2 is a bottom plan view thereof; Figure 3 is a side elevational view thereof; Figure 4 is a diagrammatical illustration of the device implantation in the anterior chamber of the eye; Figure 5 is a cross-sectional view of a thin lens optic region; Figure 6 is a front elevational view of a first alternate embodiment of the invention; Figure 7 is a bottom plan view thereof; Figure 8 is a side elevational view thereof; Figure 9 is a front elevational view of a second alternate embodiment of the invention; Figure 10 is a bottom plan view thereof; Figure 11 is a side elevational view thereof; Figure 12 is a front elevational view of third alternate embodiment of the invention; Figure 13 is a bottom plan view thereof; Figure 14 is a side elevational view thereof; Figure 15 is a diagram of a prior art MOD lens; Figure 16 is a diffraction plot thereof; Figure 17 is a diagram of an optical system of a MOD lens; and Figure 18 is a diagram of the diffractive pattern of the alternate optic embodiment of the invention. Description of the Preferred Embodiment of the Invention Referring now to Figures 1-14, there is shown a refractively corrective device 1 shaped and dimensioned for installation in the anterior chamber of a phakic or pseudophakic eye. The device consists essentially of a membrane preferably made of flexible polymethylmeth- acrylate (PMMA) . Other resilient materials such as silicone or hydrogel could also be used. The overall dimensions are approximately 12 millimeters in length, 8 millimeters in width and an overall thickness of approximately 10 to 100 microns. The membrane can be bent and even rolled or folded for insertion into the interior chamber through a small incision of no more than 2.75 millimeters in length. The membrane has enough resiliency to return to its prerolled or prefolded shape. The optic region 2 in the center of the membrane has an overall diameter of approximately 6 millimeters. The optic region is essentially constituted by what is called a "thin lens" in the fields of optics and ophthalmology. A thin lens is a refractive device of the type 3 illustrated in Figure 4 that combines a lenticular central zone 4 with a plurality of refractive rings 5 surrounding and concentric with the lenticular zone 4. In some applications, the entire optical element may be constituted by concentric rings. Those concentric rings resemble the rings of a Fresnel lens, except that instead of defining a prism, each ring has a front surface 6 espousing a continuous curve in common with the front surface of the central lenticular zone . It should be noted that this curved front surface may be convex, or concave depending upon the type of correction required and is seldom spherical, but may exhibit various degrees of asphericity as required to provide both a single diopter correction or multi-diopter correction as previously taught in my U.S. Patent No. 5,236,452 issued November 21, 1991, which patent is incorporated in this specification through this reference. The optic is typically made by machining the PMMA membrane with a laser milling machine. The two lateral portions 7 of the membrane astride the median optic region 2 are shaped to define at least two flaps 8 which are permanently bent obliquely backward in relation to the median region in order to nest intimately into the corner 9 of the anterior chamber as illustrated in Figure 3. Accordingly, the median portion and the lateral portion with their bent flaps 8 form a vault having a total sagital length S of approximately 1 millimeter whereby the membrane 1 spans the anterior chamber 10 in a direction substantially parallel to the iris 11. It should be noted that the median portion and the lateral portions exclusive of the flaps may be slightly arcuate about the transversal length central axis XX' to a total sagital length of approximately 0.5 millimeter. In which case, the height of the flaps H would be reduced to approximately 0.5 millimeter in order to obtain a total vault height or sagital length S of approximately 1 millimeter. The curvature of the membrane and the bent of flaps are permanently imparted during the fabrication of the device. Alternate embodiments of the device are illustrated in Figures 6-14. In each of these alternate embodiments, the membrane returns to its arcuate shape and backward projecting flaps 9. Each device fits within a circle having a diameter D of approximately 13 millimeters. Due to the flexibility of the membrane, this size can accommodate practically all eye sizes. In the embodiment 13 of .Figures 6-8, the surface of the membrane is reduced for maximum buoyancy. In the embodiment 14 of Figures 9-11, the flaps have an increased thickness along their edges 15 to create a larger footprint against the wall of the eye. The collar regions 16 between each flap and the main body of the membrane is thinned down to about 20 microns in order to provide flexibility with a modicum amount of resiliency. The embodiment 17 of Figures 12-14 is of a simplified shape that can provide an even larger optic zone . Referring now to Figures 15-18, in an alternate embodiment of the thin lens implant of the imvention, the optic is constituted by a multi-order difractive (MOD) lens having a surface geometry of the type disclosed in U.S. Patent No. 5,589,982 Faklis et al . ; which patent is hereby incorporated by reference into this specification. As disclosed in said patent, a MOD lens is capable of focusing a plurality of different wavelengths of light to a single focus. A diffractive structure is used having a plurality of annular zones which define zone boundaries which diffract light of each of the wavelengths in a different diffractive order to the focus thereby providing a plural or multiple order diffractive singlet. The imaging properties of a plural or multi-order diffractive (MOD) lens enable the use of the lens in conjunction with light that has either a broad spectral range or a spectrum consisting of multiple spectral bands. The MOD lens differs from standard diffractive lenses in that the phase delay or jump at the zone boundaries is a multiple of waves at the design wavelength (a multiple of 2τr, i.e., where p is an integer greater or equal to 2 , and the zone radii are obtained by solving the equation φ(r- j )=2ττpj, where φ (x) represents the phase function for the wavefront emerging from the lens). The number of 27T phase jumps, p, represents a degree of freedom allowing an optical designer to use distinct diffraction orders to focus two or more spectral components upon the same spatial location. Referring to Figure 15, the blaze profile is on one side of a substrate of optically transmissive material. The number of waves for each zone boundary is indicated as p and the phase jump of phases at each zone boundary, which are at radii rl, r2 , r3 andr4 is constant. The center of the lens is along the optical axis and is perpendicular to the plane of the planar substrate on which the profile is formed. The profile of the lens may also be a phase reversal (or Wood) profile, or a multilevel approximation to the blaze profile. The profile may be defined between substrates, rather than on a planar surface of a substrate, as shown, where the substrates on opposite sides of the profile have different indicies of refraction. The profile may be defined on a curved substrate. The zone spacing or width of the zones between the zone boundaries r ~ 's: 2 ' r 2 _r 3 ' r 3 ~r 4 are ru H period Fresnel zones. These zones are defined such that the optical path difference across the jth zone is equal to "Pλ 0 " where A/ 0 is the design wavelength, F Q is the focal length, when the illumination wavelength Λ =λ 0 and P is an integer that represents the maximum phase modulation as a multiple of 2π . In the paraxial region, the locations of the zones in the plane of the lens are given by r 2 j 2jpλ 0 F 0 ( 1 ) The optical phase introduced by the diffractive element is given by where is defined as the fraction of 2τr phase delay that is introduced for illumination wavelengths other than the design wavelength and is given by n(λ)-l a λ n(λ 0) - 1 (3) where n is the index of refraction of the material in the grating region. The maximum height of the surface relief is given by pλ 0 h m «(r) n(λ 0 )-l (4) The amplitude transmission function of the diffractive lens can be expanded as a Fourier series to give t(r)= e hiav - m) sin p-mje M m*-« (5) where sine (x) =sin (TΓX) / (TΓX) and m denotes the m-th diffraction order. The transmission function in Eq. (5) represents a diffractive lens within the paraxial approximatio . F(λ) = P λ ° FQ mk ( 6 ) The focal length in Eq. (6) is proprotional to p and inversely proportional to the illumination wavelength and the diffraction order, m. When the quantity in Eq. (6) , λ 0 /-np , is set equal to unity, several wavelengths can come to a common focus . The p letter represents a construction parameter and is usually constant across the lens radius, and the wavelengths that are focused to a common point are chosen from a set of diffraction orders (i.e., multi-order diffractive lenses). While a diffractive lens with a maximum phase modulation of 2τr can allow a mutual focus for simple harmonics of the design wavelength, the parameter p offers a mechanism to control specific wavelengths in a given band or bands that will come to a fixed focus. This property allows the design of achromats and apochromats using a single diffractive surface. The scalar diffraction efficiency, 1l of the m-th diffracted order is given by the squared modulus of its Fourier coefficient in Eq. (5), i.e. η,„ = in^a -m) ( η) The diffraction efficiency given by Eq. (7) is unity when the argument of the sine function is equal to zero. Notice that this condition can allow for high diffraction efficiency for several wavelengths. For example, consider the case of a multi-order diffractive lens operating in the visible region with p=10. Figure 16 illustrates the wavelength dependence of the diffraction efficiency for a range of diffracted orders neglecting material dispersion. The peaks in diffraction efficiency occur at precisely those wavelengths that come to a common focus (see Eq. (6) , i . e . , , λ,- ■ m (8) The wavelength bandwidth of the diffraction efficiency around a given diffracted order narrows with increasing values of p (see Eq. (7) and Figure 16) . Using Eq. (8) , is is possible to choose the parameters p and m to design a diffractive singlet that has high diffraction efficiency for specific bands in a given spectrum. The center wavelength of each of these bands comes to a focus distance F 0 behind the lens. It has been shown above that a multi-order diffractive (MOD) lens offers the potential for several wavelength components of the incident spectrum to come to a common focus. As a result, the polychromatic performance of the MOD signlet will differ substantially from the typical diffractive lens operating in a single diffraction order. Using the diffractive lens transmission function given in Eq. (5) , the optical transfer function (OTF) for the paraxial diffractive singlet as a function of wavelength may be calculated. Only the effects of the wavelength-dependent defocus and not any higher-order aberrations need to be included, since these aberrations can be accounted for by incluidng appropriate phase terms in the diffraction integrals. Figure 17 illustrates the geometry to compute the field distribution in the rear focal plane , which is given by t/ ; u,v;λ) = ~\\ U, (x,y;λ) Q p ° dxdy t where (u,v) represent the coordinates in plane II located a distance F 0 away and P(x,y) is the complex pupil function. Substituting Eq. (5) into Eq. (9) and assuming a unit-amplitude plane wave as the input gives ( 10 ) {ux ] dχdy Whθre 1 [jϋ il From Eq. (10) , it can be seen that the magnitude of the quantity e, is related directly to the amount of defocus in plane II. If other aberrations- , were present, one could construct a generalized pupil function in Eq. (10) that includes the phase errors introduced by the aberrations. The OTF is given by the autocorrelation of the generalized pupil function, suitably normalized, om f (12) where Η represents the coherent transfer function of the system . Assuming a rectangular pupil for simplicity, and using Eq . ( 10 ) , the OTF as a function of the spectral frequencies t„ , i _ r , ■ is give by where 1 is the diameter of the pupil aperture and represents the cutoff frequency. In the derivation of Eq. (13) using Eq. (12) , the cross terms in the double summation vanish due to an orthogonality condition for the diffracted orders. With reference to Eq. (13), note that the cases when p=m=a=l and when p=m and a-1, the OTf reduces to OTFifJ^ 2f Q rW A ( 15 ] which represents the diffraction-limited OTF associated with a rectangular aperture. Equation (13) illustrates the imaging characteristics of the MOD lens. It contains three main terms: a) triangle functions that represent the diffraction-limited portion of the OTF; b) the sine function, which is the diffraction efficiency in a given order, acts as a weighting function; and c) the sine terms that represent the degradation in the OTF due to defocus . It is important to note that the weighting function peaks to a value of unity whenever the argument is equal to zero. For the case of p=l, the typical diffractive lens in the visible wavelength range λ 0 Jλ =m; only the design wavelength will have high diffraction efficiency. Furthermore, the sine terms in the OTF illustrate that only the design wavelength will come to a sharp focus in the image plane (i.e. E is zero) and all other wavelength components in the band will be severely defocused (i.e., E is non-zero) . For this case when p>2, the MOD lens can allow several wavelengths to have high diffraction efficiency (i.e.,Λ- 0 /Λ =m) and a common focus (i.e., e can be zero for several discrete wavelengths) . Equation (13) describes how a MOD lens can provide superior performance in broadband or multi-spectral illumination. The previous imaging examples describe the effects of a wavelength-dependent defocus, but do not describe the effects of off-axis aberrations. In general, the MOD lens will have different wavelength-dependent aberration properties than the conventional diffractive singlet (i.e., p=l) . However, for the important case of wide- field diffractive lenses, one finds that the third-order aberration properties of the MOD lens are identical to those found for the conventional wide-field diffractive singlet. For example, a MOD landscape lens (indefinite- conjugate imaging) will have no coma, astigmatism, and Petzval curvature for each wavelength that satisfies the equation =m; hence, a MOD lens is able to provide high quality imaging in broadband or multi-spectral illumination over wide fields of view. As illustrated in the diagram of Figure 18, representing the diffractive pattern 101 of a polychromatic MOD lens that forms the optic of the alternate embodiment of the invention, the zone boundaries 102 diffract light of each wavelength in a different diffractive order to a single focus point. The phase delay or jump at the zone boundaries is a multiple of waves at the desired wavelength so that where p is an integer greater or equal to 2, and the location of radii r of a zone j , is determined by the equation. φ (r-j ) =2τrpj where φ (r) represent the phase function for the wavefront emerging from the lens. The number p of 2r phase jumps corresponds to the number of diffraction orders that can be used to bring two or more spectral components to focus at the same special location. Example I : A thin, foldable, MOD diffractive, polychromatic, intra-ocular implant according to the invention has been implemented based upon the following parameters and was shown to exhibit the following characteristics. Material : PMMA Thickness: 121 microns Diameter of corrective portion: 0.65 centimeter Power: -6 diopters Number of concentric zones: 50 Radial location and width of each zone: Zone Radial Width Number Ph; Location (microns) (millimeters) 0 0.00000 ■ 0.000 1 1 0.42564 525.636 2 2 0.60194 176.305 3 3 0.73722 135.283 4 4 0.85127 114.049 5 5 0.95176 100.479 6 6 1.04259 90.840 7 7 1.12613 83.537 8 8 1.20388 77.753 9 9 1.27691 73.028 10 10 1.34598 69.071 11 11 1.41168 65.696 12 12 1.47445 62.772 13 13 1.53466 60.206 14 14 1.59259 57.931 15 15 1.64848 55.898 16 16 1.70255 54.063 17 17 1.75495 52.398 18 18 1.80582 50.878 19 19 1.85531 49.484 20 20 1.90351 48.198 21 21 1.95051 47.007 22 22 1.99641 45.901 23 23 2.04128 44.869 24 24 2.08519 43.903 25 25 2.12818 42.998 26 26 2.17033 42.147 27 27 2.21167 41.343 28 28 2.25226 40.585 29 29 2.29212 39.866 30 30 2.33131 39.184 31 31 2.36985 38.537 32 32 2.40777 37.920 33 33 2.44510 37.332 34 34 2.48187 36.770 35 35 2.51810 36.234 36 36 2.55382 35.719 37 37 2.58905 35.227 38 38 2.62380 34.754 39 39 2.65810 34.299 (Continuation) Zone Radial Width Number Phase Location (microns) (millimeters) 40 40 2.69196 33.863 41 41 2.72541 33.442 42 42 2.75844 33.036 43 43 2.79109 32.646 44 44 2.82336 32.267 45 45 2.85526 31.904 46 46 2.88681 31.551 47 47 2.91802 31.209 48 48 2.94890 30.880 49 49 2.97946 30.559 50 50 3.00791 30.249 While the preferred embodiments of the invention have been described, modifications can be made and other embodiments may be devised without departing from the spirit of the invention and the scope of the appended claims.

Claims: CLAIMS 1. A single piece corrective device for installation in 2 the anterior chamber of a phakic or pseudophakic eye which 3 comprises: 4 a single thin, resiliently bendable membrane 5 shaped and dimensioned to span the anterior, chamber g substantially parallelly to the iris; η said membrane having a substantially constant g thickness in a range of approximately 10 to 125 microns; g said membrane comprising a corrective median 10 portion, and at least two lateral portions astride said 11 median portion wherein said corrective portion includes a 12 thin lens; and 13 said thin lens comprises a discontinuous 14 optic zone having a plurality of concentric optic rings. 1 2. The device of Claim 1, wherein said thin lens further includes a central continuous optic zone. 1 3. The device of Claim 1, wherein each of said lateral -, portions comprises at least one anchoring flap bent -. obliquely backward in relation to said median portion, and shaped and dimensioned to intimately nest into the corner of the anterior chamber. 4. The device of Claim 2, wherein said median portion and lateral portions form a vault having a sagittal length of 3 approximately 1 millimeter. 5. The device of Claim 1, wherein said membrane is made 2 of flexible PMMA. 1 6. The device of Claim 1, wherein said thin lens has 2 correction powers in a range of approximately minus 15 3 diopters to plus 15 diopters . 1 7. A method for treating optical deficiency of a patient's 2 eye which comprises: 3 installing, in the anterior chamber of said 4 eye, a one-piece, single component corrective device, said ^ device comprising: 6 a thin, resiliently bendable membrane η shaped and dimensioned to arcuately span the anterior o chamber substantially parallelly to the iris; q said membrane having a substantially 10 constant thickness in a range of approximately 10 to 125 11 microns, and comprising a corrective said median portion, 12 and at least two lateral portions astride said median 13 portion wherein said corrective portion includes a thin 14 lens having a discontinuous optic zone including a 5 plurality of concentric optic rings. 1 8. The method of Claim 7, wherein said step of installing further comprises making a corneal incision in said eye, 3 of no more than 2.75 millimeters in length; 4 curling said membrane; and 5 inserting said membrane through said 6 incision. 1 9. The corrective device of Claim 1, wherein said thin 2 lens comprises a multi-order diffractive lens. 1 10. The corrective device of Claim 9, wherein each of 2 said plurality of concentric optic rings has a ring 3 boundary with an adjacent ring and said rings are shaped 4 and dimensioned to provide a phase jump at each ring 5 boundary for at least one spectral component of a light 5 beam incident upon said lens . 11. The corrective device of Claim 10, wherein a 2 plurality of said spectral components have a given 3 wavelength and said rings are shaped and dimensioned " to 4 provide a phase jump equal to 2-πp wherein p is an integer 5 greater or equal to 1, said p and the widths of the rings g are selected to direct said spectral components to a η single focus point. 12. The corrective device of Claim 11, wherein said rings 2 are radially spaced at radii, r- obtained by solving the 3 equation φ ( l_ι ) = 2ττp where (r) represents the phase function of a wavefront emerging from said optic rings. 13. The device of Claim 9, wherein each of said lateral portions comprises at least one anchoring flap bent obliquely backward in relation to said median portion, and shaped and dimensioned to intimately nest into the corner of the anterior chamber . 14. The device of Claim 9, wherein said membrane is made of flexible PMMA. 15. The device of Claim 9, wherein said thin lens has correction powers in a range of approximately minus 15 diopters to plus 15 diopters. 16. The method of Claim 7, wherein said membrane comprises a multi-order diffractive lens. 17. The method of Claim 16, wherein said step of installing further comprises making a cornea'l incision in said eye, of no more than 2.75 millimeters in length; curling said membrane; and inserting said membrane through said incision. practically all types of refractive errors. Brief Description of the Drawing Figure 1 is a front elevational view of the preferred embodiment of the invention; Figure 2 is a bottom plan view thereof; Figure 3 is a side elevational view thereof; Figure 4 is a diagrammatical illustration of the device implantation in the anterior chamber of the eye; 0 Figure 5 is a cross-sectional view of a thin lens optic region; Figure 6 is a front elevational view of a first alternate embodiment of the invention; Figure 7 is a bottom plan view thereof; 5 Figure 8 is a side elevational view thereof; Figure 9 is a front elevational view of a second alternate embodiment of the invention; Figure 10 is a bottom plan view thereof; Figure 11 is a side elevational view thereof; „ n Figure 12 is a front elevational view of third alternate embodiment of the invention; Figure 13 is a bottom plan view thereof; Figure 14 is a side elevational view thereof; Figure 15 is a diagram of a prior art MOD lens; „,- Figure 16 is a diffraction plot thereof; Figure 17 is a diagram of an optical system of a MOD lens,- and

Inventors: NORDAN LEE T, NORDAN, LEE, T.
Applicants: NORDAN LEE T, NORDAN, LEE, T.
Application year: 2000
Main classification: A61F2
IPC codes: A61F2, G02B5