Concentric Refractive Multifocal Intraocular Lenses

1.7.1.1 Two-zone (button) Refractive Multifocal Intraocular Lenses

John Pearce implanted the first MIOL in June 1986. The Kratz-Johnson/ Nuvue MIOL (Precision Cosmet/IOLAB/Bausch & Lomb, Rochester, NY.) is a two-zone (button) PMMA refractive MIOL. It has a 7 mm optic and incorporates a 2 mm central optical element with an additional +4.00 D of refractive power.

The Progress 3 Domilens (Domilens/ Bausch & Lomb, Rochester, NY.) is a two-zone refractive multifocal IOL. The optic is 6.5 mm in diameter with a central 4.7 mm area that progresses from a mid point +5.00 D addition to a peripheral distance zone.

Both two-zone button MIOLs are pupil size dependent. Reduced pupil size increases the relative proportion of the near segment within the pupil zone; this increases the distribution of light in favour of the near zone. With the Kratz-Johnson/Nuvue a pupil less than 2 mm, if fully centred over the IOL, will result in a 100% distribution of light to the near focal point (Atebara and Millar, 1990). A 4 mm pupil – provided that the IOL is centred – results in 75% of light focused for distance and 25% for near (Percival, 1992). These designs of MIOLs are sensitive to decentration – malposition of the IOL can reduce the proportion of the near segment present within the pupil margin (Percival, 1992).

A good level of near visual acuity and spectacle independence has been found with both types of two-zone refractive MIOLs (Keates et al., 1987; Fu and Yong, 1990;

Bleckmann et al., 1996). However, the IOLs can compromise distance vision in comparison to other MIOL types (Percival and Setty, 1991), and contrast sensitivity, in bright light conditions, is reduced (Bonnet et al., 1991; Ravalico et al., 1998)

Figure 1.4 Optic of a two zone (button) refractive multifocal intraocular lens

1.7.1.2 Multiple Zone Concentric Refractive Multifocal Intraocular Lenses Multi-zone concentric refractive MIOLs have several concentric zones that differ in curvature, creating two or more refractive powers.

The Pharmacia Annular (Pharmacia, Montreal, Canada), Hoya SFX MV1 (Hoya, Tokyo, Japan), True Vista (Storz/ Bausch and Lomb, Rochester, NY.) and U370M (Ioptex/ Bausch and Lomb, Rochester, NY.) MIOLs are three-zone concentric MIOLs with a central and peripheral distance zone and middle near zone. The middle-near zone is +4.00 D for the Pharmacia Annular, True Vista and Norton U370 and +2.25 for the Hoya SFX MV1 at the IOL plane. The Nordan U370 has an aspheric transition between the zones facilitating intermediate vision.

Studies examining the effectiveness of these lenses are sparse. Optical bench tests have demonstrated an increase in depth of focus, but a potential decrease in contrast sensitivity with the Pharmacia Annular (Holladay et al., 1990). Spectacle independence and near vision were superior with the True Vista and U370M when compared with a monofocal. However, compromises in contrast sensitivity were found and reports of dysphotopsia were common (Shoji and Shimizu, 1996; Shoji and Shimizu, 2002; Leyland et al., 2002).

Only one clinical study has been published examining the Hoya SFX MV1. This study compared the MIOL with a monofocal lens, finding an extended range of focus and comparable contrast sensitivity levels. The study also reported 73% of the subjects experienced mild to severe dysphotopsia (Hayashi et al., 2009).

The Array (Abbott Medical Optics, Inc., Santa Ana, CA, USA), ReZoom (Abbott Medical Optics, Inc., Santa Ana, CA, USA), and MFlex (Rayner Intraocular Lenses Ltd, Hove, UK.) are all five-zone concentric refractive multifocal IOLs; the central distance zone is surrounded by alternating near and distance zones. The Array and ReZoom are similar in design: both have a near addition equivalent to +3.50 D at the IOL plane (approximately +2.60 D at the spectacle plane). The posterior surface of the Array optic is spherical, however, the ReZoom incorporates an aberration reducing aspheric posterior surface optic. The MFlex multifocal is available with either a +3.00 D or a +4.00 D addition and with four or five refractive zones depending on the base

2009), but further evaluation is necessary before conclusions can be derived. The MF-4 is a four-zone concentric refractive multifocal IOL with a centre near zone surrounded by alternating distance and near zones.

When compared with the two- and three-zone MIOLs, the five-zone MIOLs are less dependent on pupil size and are also minimally affected by decentration. However, the refractive zones in all refractive MIOLs are relatively large and so are still pupil-dependent. Centre-distance designs ensure the preservation of distance vision even with the smallest of pupils (Kawamorita et al., 2009). The MF-4 is a centre-near design;

studies are needed to examine the effects of small pupils on the visual outcomes with this IOL.

There are few studies that have evaluated the MF-4. Pérez and colleagues (2003) reported that visual acuities with the MF-4 were inferior when compared with a diffractive MIOL with an equivalent addition. Optical bench studies were unable to determine the disparity between the IOLs as they both produce equivalent image formations (Gobbi et al., 2007). Rau and Bach (2003) noted a relatively high level of spectacle independence with the MF-4, but a prevalence of dysphotopsia of 45%.

The Array and ReZoom five-zone refractive MIOLs have been extensively evaluated in both in vivo and in vitro studies. Such studies have reported reduced contrast sensitivity in lower lighting conditions and lower spatial frequencies with the five-zone refractive MIOLs (Montés-Micó et al., 2004; Cillino et al., 2008) whilst the prevalence of dysphotopsia is higher than with a monofocal IOL (Pieh et al., 2001; Häring et al., 2001; Cillino et al., 2008). In regards to near vision (Cillino et al., 2008), spectacle dependence (Fujimoto et al., 2010) and reading ability (Harman et al., 2008) the five-zone refractive MIOLs are superior in comparison with a monofocal IOL.

Figure 1.5 Optics of a three, four, and five zone refractive multifocal intraocular lens

1.7.2 Sectorial (Rotationally Asymmetrical) Refractive Multifocal Intraocular