3.1 Introduction

Spherical monofocal intraocular lenses (IOLs) were traditionally the artificial lenses of choice, but new-technology IOLs have since become widely desirable in the last decade. Major advances have been made in recent years for treating cataracts and presbyopia. Novel multifocal, accommodating, and toric IOLs have revolutionized cataract surgery. These new-technology IOLs improve vision quality, maintain or induce spectacle independence, correct astigmatism, correct presbyopia, and possibly restore true accommodation. Many of these new-technology IOLs are widely available throughout Europe and are currently undergoing clinical trials in the United States to attain Food and Drug Administration (FDA) approval. These innovative IOLs vary in shape, size, and composition. Monofocal IOLs have now grown into an assortment of multifocal, trifocal, pseudoaccommodative, and accommodative lenses. With many more IOLs making their way into the clinical setting, technology has brought us one step closer to making visual outcomes after cataract surgery as exceptional as vision with a healthy, natural lens.

Monofocal IOL technology, including many current models in use today, is covered in Chapter 2. These lenses do an excellent job of restoring visual quality impaired by cataracts, and they effectively correct vision in patients without astigmatism at one distance. The next step beyond monofocal IOLs is the correction of astigmatism and presbyopia, which can be accomplished to varying degrees employing different strategies as outlined in this chapter. Table 3-1 provides an overview of currently available advanced-technology IOLs.

3.2 Toric IOLs

3.2.1 AcrySof IQ SN6AT Toric IOL (Alcon)

The benefit of toric IOLs includes the treatment of cataracts and the correction of astigmatism in a single procedure. The AcrySof IQ Toric IOL is a one-piece, aspheric lens available in + 6 diopters (D) to + 34 D in 0.5 D increments with a 6 mm optic (Fig. 3.1). It consists of a hydrophobic acrylic lens with a yellow chromophore to provide protection from exposure to ultraviolet light. These toric IOLs are also offered in seven cylindrical powers. The surgeon may use an online toric calculator (available at http://www.acrysoftoriccalculator.com/) to determine the toric power required.

The most common issue with toric IOLs involves the postoperative rotation of the lens. A study by Miyake et al estimated an average misalignment of 4 to 5 degrees over the span of 2 years. ¹ Some causes of IOL rotation include shrinkage of the capsular bag, incomplete removal of ophthalmic viscosurgical devices (OVDs), and inadequate extension of haptics.

3.3 Multifocal IOLs

Multifocal IOLS are usually classified in two principal categories depending on which optic principle they rely on to provide a multifocal effect: the refractive IOLs and the diffractive IOLs. Refractive IOLs, such as the ReZoom and Array (both from Abbott Medical Optics, Inc.) have a refracting surface which gradually splits 100% of the incoming light before it reaches the retina. ³ On the other hand, diffractive multifocal IOLs, such as the Tecnis ZM 900 (Abbott Medical Optics, Inc.), separate incoming light into two different focal points—one for near objects and one for distant objects, meaning they actually are bifocal lenses. The diffractive lenses are intended to be less pupil dependent, thus preventing or at least reducing postoperative visual disturbances such as glare, haloes, or loss of contrast sensitivity. Finally, some other IOLs, such as ReSTOR (Alcon), combine these two optic principles. Both refractive and diffractive multifocal IOL designs are used today, providing multiple approaches to presbyopic correction. ^{4 ,​ 5}

3.3.1 “Bifocal” IOLs

ReSTOR (Alcon)

This multifocal IOL is an apodized diffractive biconvex lens made of a hydrophobic acrylic material. The apodized diffractive structure creates a 3.6 mm central zone with decreasing step heights (1.3–0.2 mm) and widths toward the periphery (Fig. 3.2). Therefore, it can split light energy into two main focal points to incorporate two different vision powers, distance and near. The peripheral refractive-only zone is intended to improve image quality by reducing the multifocal optical disturbances and transferring more light energy for distance vision when the pupil dilates. Three versions of this multifocal IOL have been implemented depending on the power of their add for near vision. FDA approved in 2005, the first commercially available version was the ReSTOR with a + 4 add power, followed a few years later by the + 3 D add power, and, finally, the + 2.5 D add power, which obtained European CE marking in 2012.

This first version of ReSTOR had a + 4 D add power at the lens plane, which is approximately + 3.25 D of additional power at the corneal plane. The preferred reading distance for the + 4 add was about 32 cm, which was a bit too near for some patients, whereas the newer ReSTOR + 3 add enables a reading distance up to 40 cm. ReSTOR + 2.5 D add is designed for patients willing to have sharper distance vision: with fewer diffractive zones and a larger central refractive zone, this IOL directs a higher percentage of light energy to the distance focal point.

Two different models of ReSTOR are available: the spheric model (SN60D3) and the aspheric model (SN6AD3). In the aspheric model, the anterior surface provides negative spherical aberration to compensate for the positive spherical aberration of the cornea. The posterior surface as well as the design and the material of the aspheric model are similar to those of the spheric model.

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Related posts:

1. 1 A Brief History of the Intraocular Lens
2. 2 Intraocular Lens Designs and Materials
3. 16 IOL Repositioning
4. 27 New-Technology Intraocular Lenses: The Next Generation

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