12.1 Introduction

Presbyopia-correcting intraocular lens (IOL) implantation has grown in popularity over the last few years as an effective way to reduce the need for spectacles or contact lenses after cataract surgery. Currently, there are several varieties of these lenses available on the market, including pseudoaccommodating and multifocal IOLs.

Pseudoaccommodating IOLs work, in theory, by using the action of the ciliary muscle to move the lens forward during accommodation. The true functional mechanism for these IOLs remains less certain. The only Food and Drug Administration (FDA)-approved pseudoaccommodating IOL in the United States is the Crystalens (Bausch & Lomb, Inc.) (see Fig. 9.1). ^{1 ,​ 2 ,​ 3} The Crystalens has two flexible, hinged-plate haptics that theoretically allow it to move within the capsular bag. The major drawbacks of these lenses are the inconsistent results for near visual acuity correction and capsular contraction causing the lens to tilt and reducing the quality of distance visual acuity.s. Literatur ^{,​ 5}

Multifocal IOLs (MFIOLs) can be divided into two main mechanisms of multifocality: diffractive and refractive. ^{6 ,​ 7} Multifocal IOLs have circular, annular rings, which contain different diopters of power for both distance and near vision. ⁸ The most commonly used MFIOLs in the United States are the AcrySoft ReSTOR apodized diffractive lens (Alcon) (see Fig. 9.3) and the Tecnis (Abbott Medical Optics, Inc.) (see Fig. 9.4). These lenses work by functionally splitting light into various focal planes, thereby facilitating both near and distance acuity in each eye and providing the broadest range of vision. Outside the United States, a multitude of IOLs are available, each with subtle differences in design but with overlapping clinical function and outcomes. Compared to monofocal and accommodating IOLs, MFIOLs offer increased depth of field with improved near acuity but also with a higher rate of visual disturbances.

The majority of patients report comparable distance acuity with monofocal and multifocal lenses, and most report improved near and intermediate vision with multifocal lenses.s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^{,​ 16} However, in some patients, the multifocal design may lead to significantly decreased contrast sensitivity and increased glare, halos, and dysphotopsias. ^{3 ,​ 7 ,​ 17 ,​ 18 ,​ 19 ,​ 20}

12.2 Visual Dissatisfaction in Pseudoaccommodating IOL Patients

The most common visual complaint after accommodating IOL implantation is lack of efficacy for near acuity. One study comparing the Crystalens with the two commonly implanted MFIOLs showed that the Crystalens has improved intermediate visual acuity without the glare and halos seen with multifocal lenses; however, the pseudoaccommodating lenses tended to have worse distance-corrected and uncorrected near acuity compared to the MFIOL options. ^{3 ,​ 21 ,​ 22 ,​ 23 ,​ 24} In a recent meta-analysis of four randomized, controlled studies comparing accommodating IOLs to monofocal IOLs, the authors concluded that accommodating IOLs achieved better distance-corrected near acuity between 12 and 18 months after implantation but with considerable heterogeneity of effect. The gain of near acuity on a Snellen chart was minimal and averaged approximately one line. ²³

The ability to reach a desired near visual acuity available with Crystalens may be limited by postoperative contraction within the capsular bag. A unique complication associated with the Crystalens is “Z syndrome,” which is defined by an irregular capsular contraction that occurs when one haptic bows anteriorly while the other haptic remains posterior to the capsule (Fig. 12.1). This asymmetric fibrosis can lead to tilting of the lens, which can then produce spherical aberrations, astigmatism, increased myopia, and, in some cases, chronic pain. Treatment for Z syndrome consists of neodymium:yttrium-aluminum-garnet (Nd:YAG) laser capsulotomy to the fibrosed area, which allows the lens to move back into its normal configuration. Intraoperative measures can be taken to prevent Z syndrome, such as creating an appropriately sized capsulorhexis and performing adequate cortical removal and capsular polishing; however, this postoperative complication may be unpredictable in some cases.s. Literatur

Many studies have shown that little to no accommodation actually occurs with Crystalens implantation. Zamora-Alejo et al were unable to detect an objective sign of accommodation (increased myopic response with a near target) by an autorefractor. ²¹ Marcos et al studied the axial shifts of the Crystalens within the eye and found minimal axial movement with accommodative effort. Alternatively, some of the implanted lenses in their study actually had a posterior shift with natural accommodation, which was opposite to the expected and desired movement of the lens. The authors of this study propose that the actual mechanism of action of the Crystalens may not be the axial shift that the manufacturer describes. ²⁵ Dhital et al compared the Crystalens to monofocal IOL implantation and found that neither lens had clinically significant movement inside the eye. They also found that near vision was not directly correlated with movement of the accommodating IOL. The study concluded that near acuity was partly due to increased depth of focus, but the actual mechanism of improved near vision is still unknown. ²²

12.3 Visual Dissatisfaction in Multifocal IOL Patients

The two main categories of complaints associated with MFIOLs are blurred vision and photic phenomenon. Blurred vision may be present at near, intermediate, and far distances.

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