Development And Types Of Iols

Figure 1 illustrates some of the more common types of IOLs and identifies their components. The first IOL was implanted in 1949 and was termed the "Ridley posterior chamber lens." It was made of poly(methyl methacrylate) (PMMA) and designed to resemble the characteristics of the human lens. It had two dissimilar radii of curvature, was biconvex in its shape, and weighed about 112 mg in air, making it an extremely heavy lens. To benefit from the support of an intact posterior capsule, the IOL was implanted after an extracapsular cataract extraction (Ridley, 1951). Although this original Ridley posterior chamber lens restored visual function, problems related to the weight and size of the implant, as well as its displacement into the vitreous body, limited its usefulness. The fact that the IOL produced reasonable results when complications did not ensue stimulated ophthalmologists to design other types of IOLs.

Typically, the Ridley lens was placed behind the iris and in front of the intact posterior capsule. This area, known as the posterior chamber, offers several optical and mechanical advantages. Despite the fact that early posterior chamber IOL implantation was abandoned shortly after its inception, it currently is the most popular type of IOL implantation. Other sites selected for IOL implantation were the anterior chamber and the pupillary space. The anterior chamber IOL relies on support of the peripheral iris structure and the collagen fibers of the scleral tissue in the anterior chamber angle. The first anterior chamber lenses were very heavy and generally had three or four thick footplates that rested in the peripheral anterior chamber (Strampelli, 1961; Choyce, 1958). Contact between the thick PMMA footplates and the cornea caused corneal decompensation because the endothelial cells of the peripheral cornea were damaged, thereby compromising their barrier and pump functions. As much a problem with the designs of these implants was the problem of properly sizing the diameter of the IOL to fit the dimensions of a particular eye (Moses, 1984). If the anterior chamber IOL was too long, it produced erosion into the iris and ciliary body, as well as corneal damage. If the IOL was too short, it would fail to be supported properly, causing a propelling effect in the anterior chamber, often damaging the anterior surface of the iris and the corneal endothelium.

A number of anterior chamber SOLs were developed later, each with features designed to obviate the problems of their predecessors. However, even these newer anterior chamber IOLs produced the type of tissue erosion, hemorrhage, inflammation, and corneal decompensation seen with earlier anterior chamber IOL designs (Eliingson, 1978). These lenses used finely looped haptics that were associated with micro-movement in the anterior chamber angle, breakdown of the blood—ocular barrier, adhesions around the haptic, iris chafing, and inflammatory symptoms. Although the lens optics were made of PMMA, the edges were not adequately polished. The haptics were fabricated from the kind of polypropylene used for suture material, or extruded PMMA (Apple et al., 1987). Problems with these anterior chamber lenses resulted in similar clinical complications and prompted their withdrawal from the market.

The latest anterior chamber lens designs incorporate one-piece PMMA technology, open haptics to impart greater flexibility, vaulting to lessen the likelihood of contact between the posterior surfaces of the IOL and the iris, discrete points of contact between the ends of the haptics and angle structures, and excellent polishing and finishing of the surfaces and edges of the anterior chamber lenses. Attention to modification in lens design and fabrication has made the present generation of anterior chamber IOLs acceptable.

Following early dissatisfaction with the Ridley posterior chamber IOL and anterior chamber IOLs, several surgeons used IOLs that were implanted in the pupil. These pupil- or iris-supported IOLs could be implanted after intracapsular or extracapsular surgery, did not rely on the anterior chamber angle for support, and were readily centered in the visual axis. Among the earliest designs were the Epstein collar button and Maltese cross, which was later modified as the Copeland lens (Epstein, 1959). However, the more popular style of these lenses—the Binkhorst, Worst, and Fyodorov IOLs—had PMMA optics and haptics made variously of nylon 6, nylon 66, and polypropylene (Binkhorst, 1959; Fyodorov, 1977; Worst, 1977). Evidence that nylon sutures degenerated within the eye contributed to the demise of this material (Kronenthal, 1977). Later, polyimide was used as a haptic material to support a glass optic pupil-supported IOL (Barasch and Poler (1979). For short periods, some manufacturers used platinum—iridium or titanium haptics. However, these metal-loop lenses were heavy and caused lacerations of the iris, anterior chamber hemorrhages, and corneal decompensation (Shepard, 1977).

Pupil-supported lenses popularized the concept of IOL implantation. Although they were more difficult to implant than anterior chamber IOLs, there were no problems with sizing of these lenses, thereby reducing the need to maintain a large inventory of IOLs. With the passage of time, however, late corneal decompensation occurred, often necessitating corneal transplantation and IOL removal. In addition, problems related to erosion of the iris, especially at the pupil border, developed. At times, this condition mimicked that observed with anterior chamber IOLs. Perhaps the most significant concern was the reliance on the pupil for support that not infrequently caused IOL dislocation, either partial or total, when the pupil dilated (Obstbaum, 1984). Thus, despite an acceptance of this generic-style IOL, the pupil-iris-supported lens was supplanted once the posterior chamber IOL wasl introduced,

Pearce modified the Ridley tripodal anterior chamber IOL for use in the posterior chamber. This was a solid, one-piece PMMA IOL (Pearce, 1976). Once again, as with the Ridley posterior chamber IOL, the presence of a posterior capsule was essential for implanting this lens. The two lower haptics were placed within the capsular bag, while the superior haptic was sutured through the posterior surface of the iris. This lens enjoyed good success in the hands of relatively few surgeons but, more important, served as a reawakening to the benefits of posterior chamber implantation. Shortly after this, Shearing, modifying a Barraquer anterior chamber lens, announced a new era of IOL implantation (Shearing, 1979). This lens had a PMMA optic and two J-shaped polypropylene haptics designed for placement behind the iris in front of the posterior capsule. This concept of IOL implantation achieved such success that further modifications of the initial design followed and resulted in manufacturing techniques to create one-piece PMMA IOLs with flexible haptics.

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