Conducting a clear lens extraction of the presbyopic clear lens and replacing it with a multifocal IOL provides patients with good near and quite good intermediate UCVA, as well as maintains or improves distance UCVA. In my practice, the use of new multifocal IOLs has enhanced visual performance and given patients high levels of satisfaction.

The basic principle of multifocality consists in the juxtaposition of two images in the eye, which creates simultaneous vision. The first image is sharp, and it is focused upon the retina. The second image, however, is blurred and unfocused. Cortical selection helps to neutralize the blurred image and requires cerebral adaptation. One consequence of sharing of incident light in two focuses is that there is less incident light—and therefore less contrast—at each focus.

DIFFRACTIVE MULTIFOCALS
There are two types of multifocal IOLs: diffractive (Figure 1) and refractive (Figure 2). Diffractive IOLs, such as the ReStor (Alcon Laboratories, Inc., Fort Worth, Texas), the Tecnis Multifocal (Advanced Medical Optics, Inc., Santa Ana, California), and the Acri.LISA (Acri.Tec, Henningsdorf, Germany), distribute different incident light for far or near vision, depending on the manufacturer, that allows a specific distribution. Either way, these multifocal IOLs behave like bifocals, and their optical performance is classically unaffected by decentration. When implanting a diffractive multifocal IOL, pupil size, apart from the ReStor lens, does not matter.

ReStor. This first diffractive multifocal is now injected through a 2.2-mm incision. It has 12 diffractive zones, covering the central 3.6-mm anterior lens surface. The ReStor is available in 18.00 D to 25.00 D, and the A constant is between 118.2 for ultrasound contact biometry and 118.4 for optical biometry. It adds 4.00 D at the lens plane and 3.20 D at the spectacle plane. Using apodization, this lens has been shown to allocate appropriate light energy to light levels and minimize photic phenomena. As the pupil constricts, the ReStor equilibrates light energy for either near or distant vision. When the pupil dilates, the lens catches less incident light to defocus the near image.

The ReStor is now available as a monobloc, with a blue-blocker filter; the three-piece ReStor remains available.

Tecnis Multifocal. Available in 5.00 D to 34.00 D, the diffractive pattern of the Tecnis Multifocal is placed on the posterior surface of the lens, and the prolate anterior face suppresses Z4 spherical aberration. This silicone lens adds 4.00 D at the lens plane and 2.80 D at the spectacle plane, and the A constant is 119.1. This IOL has high stability, as the PVDF haptics are C-shaped. It is implanted through a 2.8-mm incision.

Acri.LISA. LISA is an acronym for (L) light intensity distribution 65% far and 35% near; (I) independent from pupil size; (S) smooth refractive/diffractive surface profile; and (A) optimized aspheric optic. With an A-constant of 117.8, this monobloc hydrophilic lens has a hydrophobic surface treatment. The Acri.LISA is injected through a 1.8- to 2.2-mm incision, and reduces disturbing light phenomena including scattered light and halos. With the Acri.LISA, aberration correction is distributed over the whole eye.

REFRACTIVE MULTIFOCALS
Refractive multifocal IOLs, including the ReZoom (Advanced Medical Optics Inc.,) the MF4 (Carl Zeiss Meditec, Jena, Germany; and IOLtech, La Rochelle, France), and the M-Flex (Rayner Intraocular Lens Ltd., East Sussex, UK), feature several concentric optical zones. These zones vary the radius of curvature that is located on the anterior face of the lens. In each zone, incident light distribution is dependent on pupil size. Like with the diffractive multifocal IOL, each manufacturer determines the distribution of incident light.
ReZoom. This refractive multifocal IOL is the new version of the Array (Advanced Medical Optics, Inc.), and it has five optical zones with aspherical transition. From center to periphery, zones one, three, and five are devoted to far vision. One feature of the ReZoom is that the width of the zones from center to periphery are decreased, creating the balanced view optics. The lens is an acrylic IOL, and it ranges from 6.00 D to 30.00 D. The ReZoom adds 3.50 D at the lens plane and 2.50 D at the spectacle plane.

MF4. This was the first autofocus hydrophilic acrylic multifocal lens. It is implanted through a 3.0-mm incision, and should be used in patients who do not have preexisting heavy ocular pathologies. The MF4 has a 6.00-mm optic diameter, and it adds 4.00 D to lengthen the focal depth of the eye. It is available in 15.00 D to 26.00 D. The lens has a tripod design, providing self centration; one multifocal side has four refractive zones. From center to periphery, zones one and three are devoted to near vision.

M-Flex. The M-Flex refractive multifocal has an square edge. Available in 18.00 D to 23.00 D, it provides a distance dominant focus. This hydrophilic acrylic lens has either four or five annular zones, depending on the base power. It adds 3.00 D of refractive power, or 2.25 D at the spectacle plane. The M-Flex has anterior/posterior, torsional, and rotational stability.

KEYS TO SUCCESS
Patient selection is of great importance. It is best if patients are aged between 45 years and 60 years. They should have spherical ametropia and/or late contact lens intolerance. For hyperopic patients who are interested in a multifocal IOL option, refractive and diffractive multifocal IOLs are safe options, however, only diffractive IOLs should be used in myopic patients. Multifocal IOL use is increasingly required in patients who have had previous corneal refractive surgery and who naturally do not want to wear spectacles at the age of presbyopia. For these patients, the main trick remains the IOL calculation, but many of them can provide their refractive history.

Patients who are considered as contraindicated for other surgical compensation of presbyopia (eg, presby-LASIK, phakic multifocal IOLs), because of a thin cornea, narrow anterior chamber, or poor endothelium, can often be selected for multifocal IOL implantation. Contraindications to multifocals include any monophthalmic patients; those with any ocular diseases or a severe general disease that could decrease contrast sensitivity; ambylopia; patients with unrealistic visual expectations; and patients needing high levels of contrast sensitivity (eg, pilots, photographers). Take care if you decide to implant a multifocal IOL in a patient aged more than 70 years—because cerebral adaptation is uncertain—or those who are emmetropic—because they could feel a significant loss of the image's quality for far vision. If the patient has more than 1.00 D of astigmatism, they will not be able to correctly use the multifocal IOLs. In a patient with large pupils, halos could be annoying, especially when driving at night. These may also be contraindications, depending on the situation.

It is important to achieve accurate biometry readings prior to IOL implantation. I use the IOLMaster (Carl Zeiss Meditec), and I always personalize my A-constants. I use the following A-constants: ReStor, 118.4; Tecnis Multifocal, 119.1; Acri.LISA, 117.8; and ReZoom, 118. One tip is to use the new generation formulas. For myopic patients, I suggest the SRK-T. This formula may also be used for hyperopic patients receiving a ReStor. Alternatively, you may use Holladay's formula for hyperopic ReStor patients. For the Tecnis hyperopic patient, use the mean of SRK-T and Haigis, and then subtract 0.50 D.

For quality surgery, use the smallest incision possible. This will reduce the induced astigmatism that sometimes results from ocular surgery. Additionally, the rhexis should slightly overlap the optic on 360º, and the ophthalmic viscosurgical device should be completely removed from underneath the IOL. A better quality surgery will also include posterior capsule polishing.

CONCLUSION
New multifocal IOLs are a current expanding surgical option when treating presbyopia. In my own practice, the use of multifocals represented 5% to 7% of the IOLs I inserted 5 years ago. Now, this percentage has grown to 15% to 20%. It remains mandatory to carefully select the patient with a precise and complete ophthalmologic examination, and to eliminate any uncertain case, especially when beginning the multifocal use. Before surgery, do not forget to provide complete written information, describing the advantages (ie, less spectacle dependency, improved quality of life) and disadvantages (ie, side effects including halos, glare, and loss of contrast sensitivity) of multifocality. Before implantation, remember to ask patients about their daily activities and visual expectations. For example, you should discuss their driving habits, lifestyle, as well as any particular visual requirement that they may have. This will help you to choose the model of multifocal IOL that will best suit a determined patient.

Pascal Rozot, MD, is in practice at the Clinique Monticelli, in Marseilles, France. Dr. Rozot states that he has no financial interest in the products or companies mentioned. He may be reached at +33 491162211; pcrozot2@wanadoo.fr. Dr. Rozot is a member of the CRSToday Europe Editorial Board.