Advances in the Surgical Correction of Presbyopia

George O. Waring IV, MD; Duncan E. Berry, BA

Disclosures

Int Ophthalmol Clin. 2013;53(1):129-152. 

In This Article

PC-IOLs

Background

The arena of premium IOLs is changing rapidly. The current choices in PC-IOLs include refractive multifocal IOLs, diffractive multifocal IOLs, and accommodating IOLs. A proper clinician understanding of the advantages and shortcomings of each IOL design, as well as thorough patient counseling, is necessary to attain the most desirable outcome.[7] PC-IOLs can also be combined, 1 in each eye, to increase a patient's range of near-intermediate vision, although this trend is becoming less common with advancements in IOL designs.

Multifocal IOLs

As the name implies, multifocal IOLs have multiple focal points, which produce multiple images at different focal ranges. It has been confirmed clinically that the patient primarily perceives only the focused image of interest.[8–13] The 2 broad categories of multifocal IOLs in use today are refractive and diffractive lenses.

Diffractive Multifocal IOLs

Diffractive multifocal IOLs are based on the principle of diffraction, whereby light slows down and changes direction when it encounters an obstacle.[14] Diffractive multifocal IOLs utilize microscopic steps, or diffractive zones, across the lens surface.[15] As light encounters these steps, it is directed toward the distant and near focal points. The step height determines the phase delay and therefore designates to which focal point, near or distant, the light rays will be directed. The amount of light directed to the near focal point is directly related to the step height as a proportion of wavelength. Thus, at a step height of 1 wavelength, all particles would be directed to the near focal point. Similarly, a step height that is a smaller proportion of the wavelength would direct more light particles to the distant focal point. These principles are key to understanding the design differences of the 2 subtypes of diffractive multifocal IOLs. Diffractive multifocal IOLs can be further subcategorized as apodized or nonapodized.

Apodized Diffractive Multifocal IOLs

The critical feature of an apodized lens is the gradual reduction in diffractive step heights from center to periphery.[15] Thus, as pupil size increases, more diffractive zones with smaller step heights are exposed and direct a larger proportion of light particles to the distant focal point (Fig. 4). In theory, this design allows enhanced distance vision in low-light conditions, such as driving at night.[14,15] The AcrySof ReSTOR (Alcon Lab Inc., Fort Worth, TX) was approved by the FDA in 2005 and is an apodized, diffractive, single-piece, foldable, hydrophobic acrylic, posterior chamber IOL (Fig. 5; Alcon Lab Inc.).[16] The ReSTOR has a central 3.6-mm apodized diffractive optic region and a refractive peripheral portion. The combination of the apodized diffractive region and the peripheral refractive region favors distance vision in mesopic conditions.[14] The add power of ReSTOR is +4 D at the lens, which provides roughly 3.2 D of add at the spectacle plane.[17] A toric version of the ReSTOR is available in Europe but has not yet been approved in the United States.

Figure 4.

Schematic drawing of magnified surface profile of full-optic multifocal diffractive lens. Source: Davison et al.15

Figure 5.

AcrySof ReSTOR (Alcon Lab Inc.) apodized diffractive multifocal intraocular lens. Courtesy of Alcon Lab Inc.

Nonapodized Diffractive Multifocal IOLs

Nonapodized diffractive multifocal IOLs utilize diffractive steps with uniform height from the center to the periphery thereby directing an equal amount of light to the near and distant primary foci for all pupil diameters.[15] Two examples of nonapodized diffractive multifocal IOLs are the Tecnis multifocal IOL (AMO, Santa Ana, CA) and the AT LISA 809 IOL (Carl Zeiss Meditec Company, Hennigsdorf, Germany). The Tecnis multifocal IOL comes in a single-piece version (ZMB00) as well as a 3-piece version (ZMA00) (AMO).[18] As opposed to the ReSTOR, the Tecnis multifocal IOL features nonapodized diffractive steps on the posterior surface of the lens. The AT LISA 809 IOL (not available in the United States), although nonapodized, does direct light asymmetrically to the 2 focal points, in favor of the distant focal point.

Refractive Multifocal IOLs

Refractive multifocal IOLs are defined by the incorporation of 2 different powers integrated into 2 or more circular refractive zones. Because each lens zone has a different effective aperture, the image quality depends, in part, on the pupillary response to light and the accommodation reflex.[15] Approved by the FDA in 2005, the ReZoom (AMO) refractive multifocal IOL is a flexible 3-piece lens that features 5 refractive zones specifically proportioned to provide good visual function across a range of distances in varying light conditions. Zones 1 (central zone), 3, and 5 are distance dominant whereas zones 2 and 4 are near dominant and the aspheric transitions between the zones provide intermediate vision.[16] The near-dominant zones provide +3.5 D of add power that, with correction, has a near focus of 39 cm or 16 inches. The aforementioned diffractive IOL designs have largely replaced the refractive IOL designs used today.

Rotationally Asymmetric Multifocal IOLs

Although the refractive and diffractive IOLs discussed are based on the concept of rotational symmetry, there is an immerging category of IOLs which utilizes the concept of rotational asymmetry. One such lens, the Lentis Mplus LS-312 (Oculentis GmbH), consists of a surface-embedded near section that makes the IOL independent of pupil sizes >2.0 mm.[19] It is a single-piece, square-edged IOL composed of a hydrophilic acrylic material with a hydrophobic surface and is available with a +3 D or +1.5 add and received the CE mark in March 2009. Alió and colleagues reported data on 44 eyes and demonstrated mean values 3 months postoperatively of uncorrected distance visual acuity (UDVA), 0.04 logMAR±0.25 (SD); contrast sensitivity, 1.57±0.13 logCS; near vision, M0.75±0.33 at 32 cm and M0.90±0.27 at 66 cm; reading speed, 161.74 words/min; sphere, 0.08±0.58 D; astigmatism, -0.60±0.50 D; CDVA, -0.08±0.07 logMAR.[19]

The newest design based on the concept of rotation asymmetry is the FineVision IOL (Liège, Belgium) that is a trifocal design based on the idea of combining 2 diffractive profiles, 1 for distance and near and 1 for distance and intermediate.[20] The lens features 2 kinoform patterns—1 for intermediate vision and 1 for near vision. The first pattern has a +3.5 D add as the first diffraction order and the second pattern has a vergence of 1.75 D in the first order and 3.50 D in the second order. Investigators demonstrated that the FineVision IOL (Liège) provided an intermediate addition of 1.75 D.[20]

Accommodating IOLs

There are 2 general types of accommodating IOLs on the market, single-optic and dual-optic. Single-optic accommodating IOLs aim to correct presbyopia by altering the focal length of the IOL-eye optical system primarily by anterior movement of the lens and changes in the lens architecture.[21] The dual-optic accommodating IOL design is based on the observation that the degree to which an IOL can contribute to accommodation depends not only on the amplitude of axial displacement, but also on the power of the displaced IOL.[22,23] Hara et al[24] hypothesized that by adding a second optic of opposite power, a greater accommodation range can be reached.

Single-optic Accommodating IOLs

The Crystalens accommodating IOL (Fig. 6; Bausch+Lomb, Aliso Viejo, CA) is an FDA-approved single-optic lens that features flexible hinges at the plate-style haptic to facilitate anterior motion.[25] The original clinical trial reported about 1 D of accommodation.[25] Although there has been some controversy about the degree and hypothesized mechanism of accommodation, the lens has demonstrated good clinical outcomes with 88% of patients achieving 20/40 vision or better for their distance, intermediate, and near vision as compared with 36% of standard IOL patients.[21,26] One mechanism that has been suggested to contribute to the observed accommodation, or pseudoaccommodation is flexing of the optic itself as is seen during accommodation of the natural crystalline lens.[27] This mechanism contributed to the design of the Tetraflex accommodating IOL (Lenstec, St Petersburg, FL; pending FDA approval) that is a single-piece posterior chamber IOL with flexible 10-degree anteriorly angulated closed-loop haptics and a spherical optic. Sanders et al[28] demonstrated that functional reading ability was better with the Tetraflex as compared with the Crystalens with a statistically significantly higher proportion of patients reading 80 words/min or more at print sizes of 20/63, 20/50, 20/40, 20/32, and 20/25 (P=0.002). A toric version of the Crystalens is available in Europe but is not yet approved in the United States.

Figure 6.

Crystalens (Bausch+Lomb) single-optic accommodating intraocular lens. Courtesy of Bausch+Lomb.

Dual-optic Accommodating IOLs

The dual-optic accommodating IOL uses 2 lenses, 1 of high power and 1 of negative power, typically with the higher power lens anterior and the negative power lens posterior along the visual axis.[29] For example, the Synchrony IOL (Visiogen, Abbott Park, IL) has a +32 D front optic connected by spring haptics to a posterior optic of variable negative power. In clinical trials, it has demonstrated a mean accommodative range of 3.22±0.88 D. The Synchrony requires a larger 3.8-mm incision that induces postoperative astigmatism.[30]

Other Accommodating IOLs

IOL optics that can change their curvature with accommodation such as the NuLens (Nulens, Herzliya Pituah, Israel) and the FluidVision Lens (PowerVision Inc., Belmont, CA) as well as electroactive optics such as the Elenza (PixelOptics, Roanoke, VA) are in clinical trials or development.

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