Patent Application
20080269885
The present invention relates generally to intraocular lenses (IOLs), and particularly to IOLs that provide a patient with an image of a field of view without the perception of visual artifacts in the peripheral visual field.
The optical power of the eye is determined by the optical power of the cornea and that of the natural crystalline lens, with the lens providing about a third of the eye's total optical power. The process of aging as well as certain diseases, such as diabetes, can cause clouding of the natural lens, a condition commonly known as cataract, which can adversely affect a patient's vision.
Intraocular lenses are routinely employed to replace such a clouded natural lens. Although such IOLs can substantially restore the quality of a patient's vision, some patients with implanted IOLs report aberrant optical phenomena, such as halos, glare or dark regions in their vision. These aberrations are often referred to as “dysphotopsia.” In particular, some patients report the perception of shadows, particularly in their temporal peripheral visual fields. This phenomenon is generally referred to as “negative dysphotopsia.”
Accordingly, there is a need for enhanced IOLs, especially IOLs that can reduce dysphotopsia, in general, and the perception of shadows or negative dysphotopsia, in particular.
The present invention generally provides intraocular lenses (IOLs) in which one or more peripheral surfaces of the optic are designed to alleviate, and preferably eliminate, the perception of shadows that some IOL patients report.
The present invention is based, in part, on the discovery that the shadows perceived by IOL patients can be caused by a double imaging effect when light enters the eye at very large visual angles. More specifically, it has been discovered that in many conventional IOLs, most of the light entering the eye is focused by both the cornea and the IOL onto the retina, but some of the peripheral light misses the IOL and it is hence focused only by the cornea. This leads to the formation of a second peripheral image. Although this image can be valuable since it extends the peripheral visual field, in some IOL users it can result in the perception of a shadow-like phenomenon that can be distracting.
To reduce the potential complications of cataract surgery, designers of modern IOLs have sought to make the optical component (the “optic”) smaller (and preferably foldable) so that it can be inserted into the capsular bag with greater ease following the removal of the patient's natural crystalline lens. The reduced lens diameter, and foldable lens materials, are important factors in the success of modern IOL surgery, since they reduce the size of the corneal incision that is required. This in turn results in a reduction in corneal aberrations from the surgical incision, since often no suturing is required. The use of self-sealing incisions results in rapid rehabilitation and further reductions in induced aberrations. However, a consequence of the optic diameter choice is that the IOL optic may not always be large enough (or may be too far displaced from the iris) to receive all of the light entering the eye.
Moreover, the use of enhanced polymeric materials and other advances in IOL technology have led to a substantial reduction in capsular opacification, which has historically occurred after the implantation of an IOL in the eye, e.g., due to cell growth. Surgical techniques have also improved along with the lens designs, and biological material that used to affect light near the edge of an IOL, and in the region surrounding the IOL, no longer does so. These improvements have resulted in a better peripheral vision, as well as a better foveal vision, for the IOL users. Though a peripheral image is not seen as sharply as a central (axial) image, peripheral vision can be very valuable. For example, peripheral vision can alert IOL users to the presence of an object in their field of view, in response to which they can turn to obtain a sharper image of the object. It is interesting to note in this regard that the retina is a highly curved optical sensor, and hence can potentially provide better off-axis detection capabilities than comparable flat photosensors. In fact, though not widely appreciated, peripheral retinal sensors for visual angles greater than about 60 degrees are located in the anterior portion of the eye, and are generally oriented toward the rear of the eye. In some IOL users, however, the enhanced peripheral vision can lead to, or exacerbate, the perception of peripheral visual artifacts, e.g., in the form of shadows.
Dysphotopsia (or negative dysphotopsia) is often observed by patients in only a portion of their field of vision because the nose, cheek and brow block most high angle peripheral light rays—except those entering the eye from the temporal direction. Moreover, because the IOL is typically designed to be affixed by haptics to the interior of the capsular bag, errors in fixation or any asymmetry in the bag itself can exacerbate the problem—especially if the misalignment causes more peripheral temporal light to bypass the IOL optic.
In many embodiments of the IOLs according to the teachings of the invention, a peripheral region of the IOL's posterior surface is configured to direct at least some of the light rays incident thereon (via refraction by the anterior surface and passage through the lens body) to a reduced intensity region between a secondary peripheral image, formed by rays entering the eye that miss the IOL, and an image formed by the IOL. Such redirecting of some light into the shadow region advantageously ameliorates, and preferably prevents, the perception of peripheral visual artifacts by the IOL users.
In one aspect, an IOL is disclosed that includes an anterior surface and a posterior surface disposed about an optical axis, where the posterior surface includes a central region extending to a peripheral region. Once the IOL is implanted in a patient's eye, the anterior surface and the central region of the posterior surface cooperatively form an image of a field of view on the retina and the peripheral region of the posterior surface directs at least some light rays incident thereon (e.g., via refraction by the anterior surface) to at least one retinal location offset from the image so as to inhibit dysphotopsia.
In a related aspect, the peripheral region is adapted to receive at least some of the light rays incident on the anterior surface at angles in a range of about 50 to about 80 degrees relative to the IOL's optical axis. In some embodiments, the anterior surface exhibits a radius relative to the optical axis in a range of about 2 mm to about 4.5 mm, and the central portion of the posterior surface exhibits a respective radius in a range of about 1.5 mm to about 4 mm. Further, the peripheral region can have a width in a range of about 0.5 mm to about 1 mm. The optic is preferably formed of a biocompatible material having a suitable index of refraction, e.g., in a range of about 1.4 to about 1.6.
In another aspect, a focusing power provided by a combination of the IOL's anterior surface and the central region of the posterior surface is greater than a respective focusing power provided by a combination of the anterior surface and the peripheral region of the posterior surface. By way of example, such difference in the focusing powers can be in a range of about 25% to about 75%, and preferably in a range of about 25% to about 50%.
In another aspect, in the above IOL, at least one of the anterior surface or the central region of the posterior surface exhibits an asphericity, e.g., one characterized by a conic constant in a range of about −10 to about −100.
In another aspect, an edge surface can extend between the boundaries of the anterior and the posterior surfaces. In many embodiments, the edge surface is textured (e.g., it includes surface undulations with physical surface amplitudes in a range of about 0.5 microns to about 2 microns) so as to scatter light incident thereon in order to prevent the formation of a secondary image that could exacerbate dysphotopsia. Although in this embodiment the edge surface is substantially flat, in other embodiments, it is preferably highly convex to further lower the risk of positive dysphotopsia due to internal reflection of rays incident thereon.
In yet another aspect, a diffractive structure disposed on a portion of the anterior surface or the central region of the posterior surface provides the IOL with multiple foci, e.g., a near focus and a far focus.
In another aspect, an IOL is disclosed that includes an anterior optical surface and a posterior optical surface disposed about an optical axis, where those surfaces cooperatively provide a principal focusing power for generating an image of a field of view on the retina of a patient's eye in which the IOL is implanted. An annular peripheral surface surrounds the posterior surface. The annular surface is adapted to direct, in combination with the anterior surface, some light rays incident on the anterior surface to the retina, with a secondary focusing power less than the principal power, so as to ameliorate dysphotopsia. In some cases, the secondary focusing power differs from the primary focusing power by a factor in a range of about 25% to about 75% percent, and preferably in a range of about 25% to about 50%.
While in some embodiments the posterior surface and the annular peripheral surface form a contiguous optical surface, in other embodiments, they comprise separate surfaces that are connected together. Further, while in some embodiments the anterior and posterior surface have convex shapes, in other embodiments, they have other shapes, such as concave or flat.
In yet another aspect, an IOL is disclosed that includes an anterior optical surface and a posterior optical surface, which are disposed about an optical axis. The IOL further includes an annular focusing surface that at least partially surrounds the posterior surface, where the annular focusing surface is adapted to inhibit dysphotopsia once the IOL is implanted in a subject's eye.
In a related aspect, in the above IOL, the annular focusing surface can provide any of a refractive and/or diffractive focusing power. For example, the annular focusing surface can include a diffractive structure for directing light to the patient's retina so as to ameliorate, and preferably prevent, dysphotopsia.
In another aspect, the invention provides an IOL having an anterior surface and a posterior surface. The IOL can further include one or more focusing elements that at least partially surround the posterior surface for directing some of the light incident on the IOL to the retina so as to inhibit dysphotopsia. By way of example, the focusing elements can comprise a plurality of lenslets.
In other aspect, a method of correcting vision is disclosed that includes providing an intraocular lens (IOL) for implantation in a patient's eye, where the IOL comprises an anterior optical surface and a posterior optical surface disposed about an optical axis, and the posterior surface includes an annular focusing region that is adapted to inhibit dysphotopsia. The IOL can be implanted in the patient's eye, e.g., to replace a clouded natural lens.
Further understanding of the invention can be obtained by reference to the following detailed description in conjunction with the associated drawings, which are described briefly below.
The present invention generally provides intraocular lenses that include peripheral light-directing surfaces and/or optical elements that direct at least a portion of incident light to one or more retinal locations offset from a main image formed by the IOL so as to inhibit (ameliorate and preferably prevent) peripheral visual artifacts in the IOL user's visual field. The term “intraocular lens” and its abbreviation “IOL” are used herein interchangeably to describe lenses that are implanted into the interior of the eye to either replace the eye's natural lens or to otherwise augment vision regardless of whether or not the natural lens is removed. Phakic lenses, for example, are examples of lenses that may be implanted into the eye without removal of the natural lens.
By way of example, with reference to
The anterior surface 14 and the central region 20 of the posterior surface 16 have substantially convex shapes—though other shapes are possible in other embodiments—and cooperatively provide a desired focusing power, e.g., one in a range of about −20 D to about 40 D, and preferably in a range of about −15 D to about +10 D. As discussed further below, once the IOL is implanted in a patient's eye, the optical power provided by the combination of the anterior surface and the central region of the posterior surface facilitates generation of an image of a field of view on the patient's retina.
In this embodiment, the peripheral region 22 of the posterior surface 16 has, however, a substantially concave shape, and is adapted to receive peripheral light rays incident on the anterior surface at large angles relative to the optical axis OA, e.g., rays incident on the anterior surface at angles greater than about 50 degrees (e.g., in a range of about 50 degree to about 80 degrees) relative to the optical axis OA. More specifically, as shown schematically in
As shown schematically in
With reference to
The optic 12 is preferably formed of a biocompatible material, such as soft acrylic, silicone, hydrogel, or other biocompatible polymeric materials having a requisite index of refraction for a particular application. For example, in some embodiments, the optic can be formed of a cross-linked copolymer of 2-phenylethyl acrylate and 2-phenylethyl methacrylate, which is commonly known as Acrysof®.
Referring again to
Further, in this embodiment, the optic 10 is foldable so as to facilitate its insertion into a patient's eye, e.g., to replace a clouded natural lens.
In use, the IOL can be implanted in a patient's eye, during cataract surgery, to replace a clouded natural lens. During cataract surgery, an incision can be made in the cornea, e.g., via a diamond blade, to allow other instruments to enter the eye. Subsequently, the anterior lens capsule can be accessed via that incision to be cut in a circular fashion and removed from the eye. A probe can then be inserted through the corneal incision to break up the natural lens via ultrasound, and the lens fragments can be aspirated. An injector can be employed to place the IOL, while in a folded state, in the original lens capsule. Upon insertion, the IOL can unfold and its haptics can anchor it within the capsular bag.
In some cases, the IOL is implanted into the eye by utilizing an injector system rather than employing forceps insertion. For example, an injection handpiece having a nozzle adapted for insertion through a small incision into the eye can be used. The IOL can be pushed through the nozzle bore to be delivered to the capsular bag in a folded, twisted, or otherwise compressed state. The use of such an injector system can be advantageous as it allows implanting the IOL through a small incision into the eye, and further minimizes the handling of the IOL by the medical professional. By way of example, U.S. Pat. No. 7,156,854 entitled “Lens Delivery System,” which is herein incorporated by reference, discloses an IOL injector system. The IOLs according to various embodiments of the invention, such as the IOL 10, are preferably designed to inhibit dysphotopsia while ensuring that their shapes and sizes allow them to be inserted into the eye via the injector systems through small incisions.
Once implanted in a patient's eye, the IOL 10 can form an image of a field of view. By way of example, with reference to
With continued reference to
By way of further illustration,
In contrast,
By way of further illustration of the focusing function of the peripheral region of an IOL of the invention in alleviating the perception of dark shadows,
The annular peripheral region of the IOL 10 can have a variety of different surface profiles. For example,
With reference to
Some embodiments of the invention provide an IOL that includes a diffractive posterior peripheral region that sends some of the light incident on the IOL into the shadow region so as to ameliorate, and preferably prevent, dysphotopsia. By way of example,
In this embodiment, the diffractive structure 60 is formed of a plurality of diffractive zones 62, each of which is separated from an adjacent zone by a step. In this embodiment, the step heights are uniform—although non-uniform step heights are also possible in other embodiments—and can be represented by the following relationship:
wherein
λ denotes a design wavelength (e.g., 550 nm),
a denotes a parameter that can be adjusted to control diffraction efficiency associated with various orders, e.g., a can be selected to be 1;
n2 denotes the index of refraction of the optic,
n1 denotes the refractive index of a medium in which the lens is placed.
Although in this embodiment, the diffractive peripheral region has a substantially flat base profile; in other embodiments the base profile can be curved. In use, the diffractive structure 60 receives some of the peripheral light rays incident on the anterior surface, e.g., rays that are incident on the anterior surface at angles in a range of about 50 to about 80 degrees relative to the optical axis OA. The diffractive structure directs at least some of those rays to a region of the retina that is offset relative to an image formed by the IOL's primary power (e.g., to a shadow region between a secondary image formed by peripheral rays entering the that miss the IOL and an image formed by the IOL) so as to inhibit dysphotopsia. To this end, in some cases, the diffractive structure, together with the anterior surface, provides an optical power that is less than the IOL's primary power by a factor in a range of about 25% to about 75%, and preferably in a range of about 25% to about 50%.
With reference to
In some cases, the image quality of the primary image (the image formed by the IOL's anterior surface and the central region of its posterior surface) can affect the perception of shadows. Hence, in some embodiments, the anterior surface and/or the central portion of the posterior surface can exhibit a degree of asphericity and/or toricity. Additional teachings regarding the use of aspheric and/or toric surfaces in IOLs, such as various embodiments discussed herein, can be found in U.S. patent application Ser. No. 11/000,728 entitled “Contrast-Enhancing Aspheric Intraocular Lens,” filed on Dec. 1, 2004 and published as Publication No. 2006/0116763, which is herein incorporated by reference in its entirety.
In some embodiments, the peripheral region of the IOL's posterior surface includes a plurality of lenslets, e.g., in the form of focusing surfaces positioned adjacent to one another, each of which can direct light incident thereon onto a portion of the shadow region. By way of example,
In some embodiments, a diffractive structure is disposed on the IOL's anterior surface or the central region of its posterior surface so as to provide a multifocal IOL, e.g., one having a far-focus as well as a near-focus optical power. For example,
wherein
λ denotes a design wavelength (e.g., 550 nm),
a denotes a parameter that can be adjusted to control diffraction efficiency associated with various orders, e.g., a can be selected to be 1.9;
n2 denotes the index of refraction of the optic,
n1 denotes the refractive index of a medium in which the lens is placed, and
fapodize represents a scaling function whose value decreases as a function of increasing radial distance from the intersection of the optical axis with the anterior surface of the lens. By way of example, the scaling function fapodize can be defined by the following relation:
wherein
ri denotes the radial distance of the ith zone,
rout denotes the outer radius of the last bifocal diffractive zone. Other apodization scaling functions can also be employed, such as those disclosed in a co-pending patent application entitled “Apodized Aspheric Diffractive Lenses,” filed Dec. 1, 2004 and having a Ser. No. 11/000,770, which is herein incorporated by reference.
In this exemplary embodiment, the diffractive zones are in the form of annular regions, where the radial location of a zone boundary (ri) is defined in accordance with the following relation:
r
i
2=(2i+1)λf Equation (5)
wherein
i denotes the zone number (i=0 denotes the central zone),
ri denotes the radial location of the ith zone,
λ denotes the design wavelength, and
f denotes an add power.
In many embodiments, the IOL 42 provides a far-focus optical power in a range of about −15 D to about 40 D and a near-focus optical power in a range of about 1 to about 4 D, and preferably in a range of about 2 to about 3 D. Further teachings regarding apodized diffractive lenses can be found in U.S. Pat. No. 5,699,142 entitled “Diffractive Multifocal Ophthalmic Lens,” which is herein incorporated by reference.
It should be understood that various changes can be made to the above embodiments without departing from the scope of the invention.
