IN THIS CHAPTER
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Report on the evolution of intraocular lens designs.
Introduction
Cataract is the most prevalent ophthalmic disease. Although a pharmacological preventive or therapeutic treatment for this potentially blinding disease is being actively sought, the solution still appears to be many years away. Therefore, surgical treatment for cataracts, which typically includes intraocular lens (IOL) implantation, remains the only viable alternative. The implantation of IOLs is now a highly successful operation, and the safety and efficacy of the procedure are well established.
Lens Design and Fixation
In 1967 Binkhorst proposed a detailed classification of the various means of fixation for each IOL type. In a 1985 update of this classification, Binkhorst listed four IOL types according to fixation sites: anterior chamber angle-supported lenses, iris-supported lenses, capsule-supported lenses, and posterior chamber angle (ciliary sulcus)–supported lenses. By common agreement, most surgeons today differentiate lens types as iris-supported lenses, anterior chamber lenses, and posterior chamber lenses.
From the time of Ridley’s first lens implantation to the present day, the evolution of IOLs can be arbitrarily divided into six generations.
Generation I (Original Ridley Posterior Chamber Lens)
Ridley’s first IOL operation was performed November 29, 1949, on a 49-year-old woman at St Thomas’ Hospital in London. His original IOL was a biconvex polymethyl methacrylate (PMMA) disc designed to be implanted after extracapsular cataract extraction (ECCE) ( Fig. 5.2.1 ).
Generation II (Early Anterior Chamber Lenses)
As a consequence of the relatively high incidence of dislocations with the Ridley lens, a new implantation site was considered, with fixation of the lens in the angle recess. The anterior chamber was chosen because less likelihood existed of dislocation within its narrow confines. In addition, anterior chamber lenses could be implanted after either an intracapsular cataract extraction (ICCE) or an ECCE.
Late endothelial atrophy, corneal decompensation, and pseudophakic bullous keratopathy were observed with the original Baron anterior chamber lens and also developed with many subsequent anterior chamber lens designs. The entity now termed uveitis–glaucoma–hyphema (UGH) syndrome was described first when ocular tissue damage occurred that was clearly the result of poorly manufactured early anterior chamber lenses.
Generation III (Iris-Supported Lenses)
Binkhorst was an early advocate of iris-supported IOLs. His first lens was a four-loop, iris-clip IOL ( Fig. 5.2.2A ) design. Although Binkhorst initially believed that IOL contact with the iris would not cause problems, he soon noted that iris chafing, pupillary abnormalities, and dislocation developed with the early iris-clip lens. Also, in an effort to circumvent dislocation, Binkhorst made the anterior loops of his four-loop lens longer, but this led to increased corneal decompensation from peripheral touch. His initial implantations were done after ICCE, but occasionally he implanted his four-loop lens following ECCE. His positive experience with this procedure prompted him to modify his iris-clip lens design for implantation following ECCE. Binkhorst’s change from ICCE to ECCE and the introduction of his two-loop iridocapsular IOL (see Fig. 5.2.2B ) in 1965 were important advances in both IOL design and mode of fixation.
Generation IV (Intermediate Anterior Chamber Lenses)
As iris-supported IOLs underwent major modifications from the early 1950s up to the beginning of the 1980s, several designs of anterior chamber IOLs were introduced. The problems of tissue chafing and difficulties in correct sizing associated with rigid IOLs were addressed by the development of anterior chamber lenses with more flexible loops or haptics. Unlike the ill-fated, nylon-looped lenses introduced by Dannheim in the early 1950s, the fixation elements of these anterior chamber IOLs were made from more stable polymers, usually PMMA and polypropylene. The best lenses were the various rigid and flexible, open-loop, one-piece PMMA designs, such as the three- and four-point fixation Kelman IOLs. Modifications of the latter have been in use since the late 1970s and are the styles most commonly implanted today ( Fig. 5.2.3 ).
Generation V (Improved Posterior Chamber Lenses)
The return to Ridley’s original concept of IOL implantation in the posterior chamber occurred after 1975. Pearce of England implanted the first uniplanar posterior chamber lens since Ridley. It was a rigid tripod design with the two inferior feet implanted in the capsular bag and the superior foot implanted in front of the anterior capsule and sutured to the iris. Shearing of Las Vegas introduced a major lens design breakthrough in early 1977 with his posterior chamber lens. The design consisted of an optic with two flexible J-shaped loops. Simcoe of Tulsa introduced his C-looped posterior chamber lens shortly after Shearing’s J-loop design appeared. The flexible open-loop designs (J-loop, modified J-loop, C-loop, or modified C-loop) still account for the largest number of IOL styles available today ( Fig. 5.2.4 ).
One obvious major theoretical advantage that a posterior chamber IOL has over an anterior chamber IOL is its position behind the iris, away from the delicate structures of the anterior segment. The return to posterior chamber lenses coincided with the development of improved ECCE surgery. Shearing identified four major milestones that have marked the evolution of ECCE surgery: microscopic surgical techniques; phaco; iridocapsular fixation; and flexible posterior chamber lenses.
Generation VI (Modern Capsular Lenses – Rigid PMMA, Soft Foldable, and Modern Anterior Chamber)
By the end of the 1980s, surgical technique and IOL design and manufacture had advanced to a point at which the older techniques gave way to more modern ones that allowed consistent, secure, and permanent in-the-bag (capsular) fixation of the pseudophakos. A marriage between IOL design and improved surgical techniques has evolved into capsular surgery. The “capsular” IOLs are fabricated from both rigid and soft biomaterials.
The many changes in surgical techniques that occurred after 1980 and into the 1990s include the introduction of ophthalmic viscosurgical devices (OVDs), increased awareness of the advantages of in-the-bag fixation, the introduction of continuous curvilinear capsulorrhexis (CCC), hydrodissection, and the increased use of phaco. Improved small-incision surgical techniques and IOL designs have resulted in a natural evolution toward foldable lenses. Most foldable lenses today are manufactured from silicone, hydrogel, or acrylic material ( Fig. 5.2.5 ).
