Over the past 30 years, research has shown that the development and use of innovative lens designs, such as multifocal IOLs, has provided patients with independence from glasses and contact lenses. Particularly in the field of refractive lens exchange, the demand for individualized procedures is high; this demand will further increase as the quest for the ultimate solution to presbyopia continues.1-5
HISTORY OF MULTIFOCAL LENSES
The first generation of multifocal IOLs debuted in the late 1980s. The designs of these rotationally symmetric lenses were based on either the principle of diffraction or the principle of refraction (See Optical Principles). These early models, made of polymethyl methacrylate (PMMA), were rigid. In 1986, John L. Pearce, MD, of England, implanted the first two-zone refractive multifocal IOL.6 The lens’ central near addition (4.00 D) zone had a diameter of 2 mm surrounded by a larger distance zone.1 Good pseudoaccommodation resulted from miosis during use of the near segment; however, this was dependent on proper lens centration and pupil diameter.
Other refractive multifocal IOL models included a three-zone design containing two distance zones and one near zone. In this design, the near zone surrounded a central distance zone, and another distance zone was located at the periphery of the lens (Storz True Vista; no longer available).1,7 Later three-zone lens designs included the 83L and 83S (Morcher GmbH, Stuttgart, Germany), which used an asymmetric approach to light distribution. With the 83L, 70% of light was devoted to distance vision and 30% to near vision; this lens was implanted in the dominant eye. Light distribution was reversed in the 83S, which was implanted in the fellow eye.7
Further multifocal refractive lens designs with up to seven zones were not as successful.1 An exception was the five-zone refractive multifocal Array IOL (Abbott Medical Optics Inc., Santa Ana, California; no longer available). First introduced in 1992 as a one-piece PMMA model, the Array combined aspheric and spherical optical surfaces with progressive transitions between zones to improve image quality. Later, the material and design of the Array were modified to create a three-piece lens (SA-40N) with silicone optic and PMMA haptics.1 These lens models were early iterations of the zonal refractive design now used in the ReZoom multifocal IOL (Abbott Medical Optics Inc.).
In 1987, the 3M Company (St. Paul, Minnesota) brought the first three-piece diffractive multifocal IOL to market. The 815E had a convex-concave optic that was later replaced by a biconvex model, the 825X. Typical diffractive lens designs have approximately 30 concentric rings, located on the posterior IOL surface, with 2-µm height differences. Such designs follow the principle of diffraction, which was described by Thomas Young in the 18th century. Later, Pharmacia (now Pfizer, New York, New York) developed a one-piece diffractive lens, the 811E.1
These diffractive IOL technologies were subsequently sold, as neither of these companies remains in the IOL business. The 3M diffractive technology is now the basis for the central apodized diffractive zone of the combination refractive-diffractive AcrySof ReStor multifocal IOL (Alcon Laboratories, Inc., Fort Worth, Texas), and the Pharmacia technology is now the basis of the diffractive Tecnis Multifocal IOL (Abbott Medical Optics Inc.).
MORE RECENT DEVELOPMENTS
Despite good functional results with this first generation of multifocals, the initial euphoria quickly passed. By the late 1990s, surgeon surveys showed widespread reservations regarding the use of multifocal IOLs. In the past 10 years, however, improved surgical techniques, increased knowledge of patient selection criteria, and the use of careful informed consent, along with changes in modern lens designs, have extended indications and once again increased the popularity of multifocals.
These more recent multifocal lens designs have led to a variety of surgeon preferences. For instance, some surgeons implant contrasting multifocal IOL models in the two eyes of the patient. Known as mix and match or custom match, this strategy is thought to enhance the strengths and reduce the weaknesses of the optical principles of each IOL, thus optimizing visual acuity for all distances. A prerequisite is that the patient’s distant-dominant eye is determined before surgery. Refractive and diffractive designs such as the ReZoom and Tecnis or the 3.00 and 4.00 D near additions of the same multifocal IOL type, such as the AcrySof ReStor or the M-flex (Rayner Intraocular Lenses Ltd., East Sussex, London), are typical combinations.
Surgeons may also prefer specialized multifocal IOLs, such as toric multifocal or additive multifocal IOLs, for certain indications. In patients with presbyopia and more than 1.50 D of astigmatism, toric multifocal IOLs are a good option.
The M-flex T was the first available toric multifocal lens. Based on a multizonal refractive aspheric optic design, the lens has either four or five annular zones, depending on the IOL base power (Table 1). The lens was first implanted at the University of Heidelberg in 2006. Like the monofocal Tflex, the M-flex T is made of a hydrophilic acrylic material and features a 360° sharp optic edge to prevent posterior capsular opacification. Currently, three other multifocal toric IOL models are available (Table 1), the AT.LISA Toric 466TD (Carl Zeiss Meditec, Jena, Germany), the Lentis Mplus toric (Oculentis GmbH, Berlin, Germany), and the AcrySof ReStor Toric (Alcon Laboratories, Inc.).
The Sulcoflex IOL (Rayner Intraocular Lenses Ltd.; see Duet Implantation: An Update) and the Add-On IOL (Dr. Schmidt Intraocularlinsen/HumanOptics AG, Erlangen, Germany) are additive or supplementary lenses that are intended to be implanted in the sulcus of pseudophakic eyes (Table 1). The advantage of additive multifocal IOLs is that they are easily explanted or exchanged; they offer the possibility to correct residual refractive errors and presbyopia after cataract or refractive surgery and offer a good option in cases of dynamic refraction changes, such as after penetrating keratoplasty.
CONCLUSION: REALISTIC EXPECTATIONS
A variety of sophisticated multifocal IOLs are now available, allowing individualized refraction correction and a greater chance for spectacle independence. Nevertheless, due to the multifocal IOL principle of separating light into two or more foci, patients should be made aware of an accompanying period of neural adaptation to the new visual perception, along with reduced contrast sensitivity and the possibility of nighttime photic phenomena such as halos. Detailed informed consent prior to surgery is mandatory.
Recent developments in this field, such as foldable and progressive multifocal IOLs and new aspheric diffractive multifocal IOL models, combined with improved surgical techniques have helped to minimize initial concerns such as decentration, reduced contrast sensitivity, or glare and halos. To determine which multifocal IOL type best fits the personal needs of the patient, his or her distance preferences must be clarified preoperatively—especially because there are individual differences in defining near vision that include 30, 40, and even 70 cm. Moreover, the patient should be informed before surgery that there is no absolute guarantee of spectacle freedom. Patient selection and informed consent, as well as realistic patient expectations, remain important parameters for a successful postoperative result.
Gerd U. Auffarth, MD, is Acting Chairman of the Department of Ophthalmology, University of Heidelberg, Germany. Professor Auffarth states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: email@example.com.
Tanja M. Rabsilber, MD, practices at the International Vision Correction Research Centre, Department of Ophthalmology, University of Heidelberg, Germany. Dr. Rabsilber states that she has no financial interest in the products or companies mentioned; however, the International Vision Correction Research Center of the University of Heidelberg has received research grants from all companies mentioned. She may be reached at e-mail: firstname.lastname@example.org.
TANJA M. RABSILBER, MD; AND GERD U. AUFFARTH, MD
The optical principles of early generations of multifocal IOLs were classified as either refractive or diffractive. In 2009, a third technology received the Confirmité Européenne (CE) Mark: a segmental multifocal IOL design.1-6 Table 1 provides a list of available diffractive and refractive multifocal IOLs; segmental multifocal IOLs and combined refractive-diffractive IOLs are listed in Table 2.
Refractive optic principle. Multifocal IOLs with a refractive optic principle consist of different refractive zones that create several foci dependent on the pupil diameter. The advantage of these designs is that intermediate distances can be better covered; however, the ability to read small print size at 30 to 40 cm can be limited. Postoperative results depend on good centration and proper pupil diameter.1-5
Diffractive optic principle. Multifocal IOLs that use a diffractive optic principle are pupil independent. They distribute incoming light rays to two principal focal points, a near and a distance vision focus.1-5 These IOLs employ a refractive anterior lens surface and a diffractive posterior surface with approximately 30 concentric rings. Steps of 2 µm separate the rings, creating a grid that diffracts and separates the incoming light rays. Due to optical principles, 41% of the incoming light is distributed to each of the foci, and 18% is lost to light scatter.1
Other multifocal IOL models combine both optical principles. Table 2 lists examples of these lenses.
Segmental multifocal IOLs. The Lentis Mplus (Oculentis GmbH, Berlin, Germany) is included in this new class of multifocal IOLs. It combines an aspheric, asymmetric distance-vision zone with a sector-shaped near-vision zone of 3.00 D. This design allows seamless transition between the zones.6 There are two spherical surfaces with different radii, one main surface and an embedded surface, to create two defined focal points. The design principle of the surfaceembedded sector segment allows the IOL’s multifocality to function independent of pupil size. A prerequisite for the best possible effect of the Lentis Mplus is positioning its optical axis on the line of sight and ensuring inferior positioning of the sector-shaped reading zone.
This lens design was evaluated in a European multicenter study and received the CE Mark in March 2009. One year after surgery, the 37 eyes evaluated at the University of Heidelberg site showed UCVA of 0.2 and BCVA of 0.0 logMAR (median). Near UCVA and BCVA were both 0.1 logMAR, and distance-corrected near UCVA and BCVA were 0.2 logMAR. Median near addition accepted was 0.00 D.
Reliable IOL power calculation was achieved, with a median difference between target and achieved spherical equivalent of only 0.17 D. The median stable postoperative refraction was 0.00 D. Defocus curve examination revealed two clear peaks at 0.00 and approximately -2.50 D, which are explained by the IOL’s two foci. Additionally, good visual results were obtained in the intermediate range of -1.00 D. On average, over a range of 4.00 D (between 1.00 and -3.00 D), a visual acuity value of 0.3 logMAR or better was achieved.
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- Alió JL,Piñero DP,Plaza-Puche AB,Chan MJ.Visual outcomes and optical performance of a monofocal intraocular lens and a new-generation multifocal intraocular lens. J Cataract Refract Surg.2011;37:241-250