CHAPTER 5

Intraocular Lenses

The history of intraocular lenses (IOLs) began in 1949, when English ophthalmologist Harold Ridley implanted the first polymethylmethacrylate (PMMA) IOL in London. Ridley made 2 decisions that were fortuitous for the development of IOL implantation: he used extracapsular cataract extraction (ECCE), and he placed the IOL in the posterior chamber. In addition, he experienced the first IOL complication, a power error of 16 D. Initially, other ophthalmologists strongly opposed the use of IOLs, and it took years of development and perseverance for the IOL to become the standard it is today. For his pioneering contributions to this technology, Ridley was knighted by Queen Elizabeth II in 2000, a year before his death.

Theoretically, implantation of an IOL is the optimal form of aphakic correction. Correction with aphakic spectacles can cause numerous difficulties, including image magnification, ring scotomata, peripheral distortion, a “jack-in-the-box” phenomenon (in which images pop in and out of view), and a decreased useful peripheral field. Most of these aberrations and distortions derive from placement of the spectacles anterior to the pupillary and corneal planes.

This chapter focuses on the optical considerations relevant to IOLs. For more surgical information with respect to IOLs, see BCSC Section 11, Lens and Cataract.

Intraocular Lens Designs

Classification

IOLs can be categorized by

implantation site (anterior chamber, posterior chamber, or prepupillary [no longer used] plane; Fig 5-1)

optic profile (biconvex, planoconvex, or meniscus; see Fig 5-1)

optic material (PMMA, glass, silicone, acrylic, collamer, or hydrogel) haptic style (plate or loop)

sphericity (spheric, aspheric) and toricity wavelength feature (UVor blue-light blocking) focality (monofocal, bifocal, or multifocal)

degree of accommodation

edge finish (ridge, square, or sharp) power (plus, minus, or plano)

type of correction (phakic IOL or aphakic IOL)

The number of factors to consider requires that the surgeon know how to select the best IOL design for each patient’s needs.

Figure 5-1 The major types of intraocular lenses (IOLs) and optics. A, Anterior chamber lens. B, Prepupillary lens (no longer used). C, Posterior chamber lens in the capsular bag. D, Posterior chamber lens in the ciliary sulcus. E, Biconvex optic. F, Planoconvex optic. G, Meniscus optic. (Redrawn b y C. H. Wooley.)

Background

In the 1970s, surgeons implanting IOLs included those who used intracapsular cataract extraction (ICCE) and those who used small-incision phacoemulsification (phaco). The IOL optic was made from PMMA, with supporting haptics of metal, polypropylene, or PMMA. The rigidity of these materials required that the small phaco incision be enlarged for IOL insertion. However, following the introduction of a foldable optic (made from silicone) in the late 1980s, enlargement was no longer required, and the combination of phaco and IOL implantation became the standard of care.

The 2 basic lens designs currently in use are differentiated by the plane in which the lens is placed (posterior chamber or anterior chamber) and by the tissue supporting the lens (capsule/ciliary

sulcus or chamber angle) (see Fig 5-1).

The effect of lens material on factors such as posterior capsular opacification (PCO) has been investigated. Earlier studies suggested that IOLs made from acrylic are associated with lower rates of PCO than are those made from silicone or PMMA. However, more recent studies suggest that lens edge design is a more important factor in PCO than is lens material, as Hoffer proposed in 1979 in the lens edge barrier theory. IOLs with an annular, ridge edge or a square, truncated edge create a barrier effect at the optic edge that reduces cell migration behind the optic and thus reduces PCO (Figs 5-2, 5-3, 5-4). The ridge concept led to the development of partial-ridge and meniscus IOLs, which were used for a time, and the sharp-edge designs now in use.

Figure 5-2 Schematic illustrating the concept of a tenfold increase in pressure (green arrow) at the edge of an IOL.

(Courtesy of Kenneth J. Hoffer, MD.)

Figure 5-3 A, Hoffer annular ridge IOL. B, Kratz-Johnson posterior chamber IOL. (Courtesy of Kenneth J. Hoffer, MD; part B

redrawn b y C. H. Wooley.)

Figure 5-4 Increasing the pressure at the edge of an IOL leads to a blockage of cells to the central posterior capsule (A, B). C, The cell blockage as it appears on an electron micrograph. (Courtesy of Kenneth J. Hoffer, MD.)

Plano IOLs are available for patients whose eyes require zero (or minimal) power in the aphakic state (ie, patients with very high myopia). The presence of an IOL helps maintain the structural integrity of the anterior segment and reduces the long-term incidence of retinal tears and detachments.

“Piggyback” lenses (ie, 2 IOLs in 1 eye; biphakia), implanted either simultaneously or sequentially, may be used in 2 situations: (1) when the postoperative IOL power is incorrect and (2) when the needed IOL power is higher than what is commercially available. Minus-power IOLs can be used to correct extreme myopia and (as piggybacks) to correct IOL power errors.

Current IOLs are foldable, injectable, aspheric, sharp edged, and single piece (or three piece), and they have higher refractive indices; together, these features allow for implantation through smaller incisions than used for the earlier designs. The historical IOL designs and the alterations that led to the current IOL designs now in use are described in Appendix 5.1 at the end of the chapter.

Apple DJ. Influence of intraocular lens material and design on postoperative intracapsular cellular reactivity. Trans Am Ophthalmol Soc. 2000;98:257–283.

Hoffer KJ. Hoffer barrier ridge concept [letter]. J Cataract Refract Surg. 2007;33(7):1142–1143; author reply 1143.

Nagamoto T, Fujiwara T. Inhibition of lens epithelial cell migration at the intraocular lens optic edge: role of capsule bending and