The human eye is the sensory organ for reacting to light. As shown in FIG. 1, the anatomical structure of an anterior segment of the eye 10 is shown and includes a transparent outer layer, the cornea 12, that is continuous with an opaque sclera 14 forming the lateral white portion of the eye 10. The cornea 12 encloses an anterior chamber 16 and posterior chamber 18, both filled with aqueous humor. The anterior and posterior chambers 16, 18 are separated by the iris 20, which is a circular, muscular structure that controls the diameter of the centrally-disposed pupil 22 and provides the color portion of the eye 10.
Light enters the eye 10 through the cornea 12, passes through the aqueous humor of the anterior chamber 16 and the pupil 22 to the lens 24. The lens 24 is a transparent, biconvex structure that focuses incoming light onto the retina (not shown). Suspensory ligaments, or zonules 26, suspend the lens 24 from ciliary bodies 28, which are muscular structures that contract to affect the convexity, i.e., shape, of the lens 24 and thereby adjust the focal distance of the eye 10. The lens 24 itself is comprised of an outer membrane, the capsular bag 30, surrounding a group of compressed cells, the nucleus 32, and a less dense compression of cells, the cortex 34.
Cataracts are a medical condition that is manifested as decreased transparency, or clouding, of the lens 24 within the eye 10. The clouding may occur to any portion of the lens 24, including the nucleus 32, the cortex 34 and/or the capsulor bag 30. Cataracts generally develop bilaterally, i.e., affecting both eyes, and to varying degrees ranging from a slight clouding to complete opacity and greatly reduce the transmission of light through the lens 24 to the retina (not shown). If left untreated, cataracts may result in blindness.
One surgical procedure for the treatment of cataracts, illustrated in FIGS. 2-4, is an Extra-Capsular (“ECCE”) surgery that includes capsulorrhexis, or a partial removal of an anterior portion of the capsular bag 30. While not limiting, the capsulorrhexis may be created by cutting and may have a diameter of approximately 5 mm. The cortex 34 (FIG. 1) and the nucleus 32 (FIG. 1) portions of the lens 24 are removed through the opening, defined by a capsulorrhexis edge 38, while the remaining portion of the capsular bag 30 is retained. An intraocular lens (“IOL”) 40 then replaces the cortex 34 (FIG. 1) and the nucleus 32 (FIG. 1).
The IOL 40, illustrated in greater detail in FIGS. 4A and 4B according to one embodiment, includes a transparent, biconvex structure 42 (though other lens structures may be used) constructed from a plastic, silicone, or acrylic material selected to replicate the refractive index and accommodation, or adjustable optical power, of the native lens 24 (FIG. 1). The biconvex structure 42 includes an anterior portion 44 and a posterior portion 46 that converge at a circumferential, lateral edge 48. While the circumferential edge 48 is specifically illustrated as a lateral wall, it would be understood that the length of the lateral wall may vary and may in fact be an edge of minimal thickness.
Two diametrically opposed haptic members 50 extend radially outwardly from the biconvex structure 42 and are generally oriented to be planar; however, angulated haptic members are also known and may be used if desired. The haptic members 50 are configured to engage the capsular bag 30 (FIG. 2) and to suspend the IOL 40 at a desired position. While the haptic members 50 are illustrated as radially extending projections, or arms, other embodiments and structures are known to those of ordinary skill in the art.
During cataract surgery, the placement of the IOL 40 may vary. For example, one conventional surgical method, shown in FIG. 2, positions the IOL 40 within the capsular bag 30 such that the haptic members 50 engage an inner surface of the wall of the capsular bag 30 and the IOL 40 is located generally centrally within the capsular bag 30. FIG. 3 illustrates an alternative position for the IOL 40, wherein the IOL 40 positioned within the posterior chamber 18 with the haptic members 50 extending into the ciliary sulcus 52.
Positioning the IOL 40 anterior to the capsular bag 30 within the posterior chamber 18 has several potential disadvantages, including possible decentralization of the IOL and/or posterior iris chafing. Thus, placement of the IOL 40 within the capsular bag 30 may be preferred. However, capsular bag fixation may result in negative dysphotopsia (“ND”), which is a visual phenomenon that occurs after an uncomplicated cataract surgery. Symptoms include a shadowing in the temporal field of vision.
The etiology of ND is unknown, but symptoms may be relieved with a second surgery, known as the piggyback method, which is illustrated in FIG. 4. As shown, the conventional piggyback method includes the first IOL, which was previously positioned within the capsular bag 30, and a second, later positioned IOL, which is placed anterior to the capsular bag 30 as shown in FIG. 4. This approach, while improving the symptoms of ND, may again lead to posterior iris chafing. Also, the alternative approach of placing both IOLs within the capsular bag may lead to interlenticular opacification (“ILO”).
Thus, there exist a need for an IOL and surgical method that provides the benefits of a capsular bag fixation but does not result in ND.