Introduction
With extraordinary advances in instrumentation and techniques for refractive surgery, there are now many options for the surgical correction of myopia, hyperopia, and astigmatism. However, the surgical treatment of presbyopia remains a formidable challenge. While the ametropias reflect static incongruities in the eye’s optical system, presbyopia reflects an acquired loss of the eye’s dynamic function of accommodation. Thus while the surgical correction of ametropias requires only a static alteration in the optical system, the correction of presbyopia requires the restoration (or replacement) of a dynamic process frequently combined with the concomitant correction of ametropia. Therefore the surgical approach for presbyopia correction is a unique challenge.
Common methods to address presbyopia include induction of myopia, induction of corneal multifocality, and scleral expansion and relaxation. However, the most promising approach is lenticular surgery with implants capable of providing spectacle independence for all vision distances (far, intermediate, and near) to increase the quality of life of the patient. One of the main treatment modalities for pseudophakic presbyopia is implantation of modern multifocal intraocular lenses (IOLs). The idea of using multifocality to compensate for the loss of accommodation dates back more than two centuries, when Benjamin Franklin invented bifocal glasses in 1784. Spectacle correction of presbyopia relies on the convergence component of the near triad (accommodation, convergence, and miosis) and the inferior field location of most near work. The translating multifocal contact lens designs use this as well, while the aspheric and concentric contact lens designs take advantage of miosis associated with near vision.
Unlike spectacles, multifocal IOLs provide simultaneous focus of distant, intermediate, and near objects on the retina, allowing the higher levels of visual processing to determine which image to regard. Issues relating to the optics of multifocality, lens designs, clinical outcomes, and surgical considerations are discussed in this chapter.
Optics of Multifocality ( and )
For a multifocal IOL to provide good image quality at different distances, incoming rays of light with vergences corresponding to these distance (far, intermediate, and near) objects must be focused on the retina simultaneously. This is achieved through the use of two (or more) distinct focal points, with the primary focal point for distance focus and secondary focal points for near and intermediate foci. There are two basic design approaches that use different optical principles to achieve multifocality refractive and diffractive optics.
The refractive symmetric multifocal lenses consist of multiple concentric radially symmetric zones that provide different focal lengths. By varying the curvature of the anterior or posterior surface of the lens, light is refracted differently by each zone. The zones can be either spherical or aspherical ( Fig. 39.1 ). This type of IOL is dependent on pupil size.
Refractive lenses with rotational asymmetry were introduced in 2009. The design of this type of lens includes a segment embedded in the lower half of the optic with the required optical power for near vision. The inferior segment has a progressive change of radius of curvature to provide adequate near vision ( Fig. 39.2 ). Diffractive multifocal lenses ( Fig. 39.3 ) achieve multifocality through the Huygens-Fresnel principle. Small gratings along the primary curve of the lens diffract light away from the primary (distance) focus toward a secondary (near) focus. The width of each diffraction grating becomes smaller as the distance from the center of the lens increases to provide higher angles of diffraction. By varying the size and pattern of the rings, the relative distribution of light energy and the location of the focal points can be specified. The pupil dependency varies among different IOL models. Recently, diffractive trifocal IOLs that provide three principal foci for distance, intermediate, and near vision became available for clinical use.
Another recent IOL technology is the extended range of focus IOL technology that combines two complementary technologies: an echelette surface and an achromatic design. The former is a diffraction grating that extends the range of vision, and the latter corrects chromatic aberration to enhance contrast sensitivity.
Formerly, a progressive multifocal aspherical IOL was introduced that utilizes an appropriate spherical aberration at the pupil’s center and corresponding higher-order aberrations at the pupil’s periphery to increase the depth of focus to generate progressive multifocality. Its optical design consists of three zones. The inner and middle zones have different spherical aberrations with opposite signs, whereas the outer one is a monofocal zone.
Table 39.1 shows the most common multifocal IOLs available on the market.
| Lens (Manufacturer) | Lens Design | Material (Optic/Haptic) | Size, mm (Optic/Total) | Asphericity | Implant Location | Add |
|---|---|---|---|---|---|---|
| AcriDIFF (Care Group) | Diffractive-refractive/bifocal | Hydrophobic acrylic | 6/12.5 | Yes | Bag | +3.25 |
| Acriva Reviol MF 613 (VSY Biotechnology) | Diffractive-refractive/bifocal | Hydrophobic acrylic | 6/13 | Yes | Bag | +3.75 |
| Acriva Reviol MFB 625 (VSY Biotechnology) | Diffractive-refractive/bifocal | Hydrophobic acrylic | 6/12.5 | Yes | Bag | +3.75 |
| Acriva Reviol MFM 611 (VSY Biotechnology) | Diffractive-refractive/bifocal | Hydrophobic acrylic | 6/11 | Yes | Bag | +3.75 |
| Acriva Reviol Tri-ED 611 (VSY Biotechnology) | Active-diffractive trifocal+EDOF/achromatic | Hydrophobic | 6.0/11.0 | Yes | Bag | +3.00/+1.50 |
| AcrySof IQ PanOptix (Alcon) | Diffractive/trifocal | Hydrophobic acrylic | 6.0/13.0 | Yes | Bag | +3.25 and +2.17 |
| Acrysof IQ ReSTOR MN6AD1 (Alcon) | Diffractive, apodized/bifocal | Acrylic copolymer | 6.0/13 | Yes | Sulcus | +3.0 |
| Acrysof IQ ReSTOR SN6AD1 (Alcon) | Diffractive, apodized/bifocal | Hydrophobic acrylic | 6.0/13 | Yes | Bag | +3.0 |
| AF-1 iSii (Hoya) | Refractive | Hydrophobic acrylic | 6.0/12.5 | Yes | Bag | +3.0 |
| AT LISA 809M/MP (Zeiss) | Diffractive/bifocal | Hydrophilic acrylic | 6.0/11.0 | Yes | Bag | +3.75 |
| AT LISA tri 839MP (Zeiss) | Diffractive/trifocal | Hydrophilic acrylic | 6.0/11.0 | Yes | Bag | +3.33 and +1.66 |
| Diff-aA and Diff-aAY (Humanoptics) | Diffractive/bifocal | Hydrophilic MicroCryl | 6.0/12.5 | Yes | Bag | +3.50 |
| FineVision (PhysIOL) | Diffractive/trifocal | Hydrophilic acrylic | 6.15/10.75 | Yes | Bag | +3.50 and +1.75 |
| iDIFF Plus 1-P and 1-R (Care Group) | Diffractive/refractive/bifocal | Hydrophilic acrylic | 6.0/11.0/12.50 | Yes | Bag | +3.0, +3.50, +4.0 |
| Lentis Comfort LS-313MF15 (Oculentis) | Refractive/bifocal | HydroSmart acrylate copolymer Hydrophobic surface | 6.0/11.0 | Yes | Bag | +1.50 |
| Lentis Mplus LS-313 MF and Lentis MplusX LS-313 MF (Oculentis) | Refractive/bifocal | HydroSmart acrylate copolymer Hydrophobic surface | 6.0/11.0 | Yes | Bag | +3.0 |
| M-flex 630-F and 580-F (Rayner) | Refractive/bifocal | Hydrophilic acrylic | 6.25/12.50 5.75/12.0 | Yes | Bag | +3.00/+4.00 |
| Miniwell Ready (SIFI) | Refractive/progressive/EDOF | Hydrophilic-hydrophobic copolymer | 6.0/10.75 | Yes | Bag | — |
| ReZoom NXG1 (Abbott) | Refractive/bifocal | foldable acrylic | 6.0/13.0 | No | Bag | +3.50 |
| SeeLens (Hanita Lenses) | Diffractive adodized/bifocal | Hydrophilic acrylic | 6.0/13.0 | Yes | Bag | +3.0D |
| Sulcuflex 653 F (Rayner) | Refractive/bifocal | Hydrophilic acrylic | 6.50/14.0 | No | Sulcus | +3.50 |
| Tecnis MF ZKB00 (Abbott) | Diffractive/bifocal | Hydrophobic acrylic | 6.0/13.0 | Yes | Bag | +2.75 |
| Tecnis MF ZLB00 (Abbott) | Diffractive/bifocal | Hydrophobic acrylic | 6.0/13.0 | Yes | Bag | +3.25 |
| Tecnis MF ZMB00 (Abbott) | diffractive/bifocal | Hydrophobic acrylic | 6.0/13.0 | Yes | Bag | +4.00 |
| TECNIS Symfony ZXR00 | Achromatic/diffractive/echelette extend range of focus | Hydrophobic acrylic | 6.0/13.0 | Yes | Bag | — |
| VERSARIO (Bausch & Lomb) | Diffractive/bifocal | Hydrophilic acrylic | 6.0/11.0 | Yes | Bag | +3.75 |
| VERSARIO 3F (Bausch & Lomb) | Diffractive/trifocal | Hydrophilic acrylic | 6.0/11.0 | Yes | Bag | +3.00 and +1.50D |
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