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Up Front | Sep 2008

Refractive Lens Exchange: Monofocal or Multifocal IOLs?

Refractive lens exchange (RLE) consists of removal of the clear crystalline lens and its replacement by an IOL to correct the preoperative refractive error. It may be indicated in patients with high refractive errors to partially reduce or eliminate dependence on optical correction when a more conservative approach is not acceptable.

RLE is frequently used in presbyopic patients with relevant refractive errors requiring optical correction for distance and near vision, such as hyperopic patients, but the procedure may also be used in myopic and astigmatic patients to reduce or eliminate the use of optical correction after surgery.

Three different IOL technologies can be used to provide good distance and near vision after RLE: (1) aspheric monofocal IOLs, (2) bi- or multifocal IOLs, and (3) accommodating IOLs.

Monofocal aspheric IOLs have the ability to direct all light rays that pass through the optical zone to the same focal point on the retina. The aspheric optic gradually decreases power from the center to the periphery of the lens, creating an image with better resolution and contrast than standard spherical IOLs provide. This aspheric quality improves the quality of visual acuity, particularly in patients with larger pupils and during night activities (Figure 1). However, due to the monofocal property of these IOLs, they must be used with a pseudophakic monovision technique to provide spectacle independence after surgery.

Westsmith first described the monovision technique in 1958, suggesting presbyopic correction with contact lenses in phakic patients.1 It was subsequently adapted for laser refractive surgery and for patients undergoing bilateral cataract surgery. In these techniques, one eye is corrected for distance vision (emmetropia) and the fellow eye for near vision (myopia).2-4

Recently, we presented a paper5 showing our results in a series of 38 patients treated using the pseudophakic monovision technique. At 6-month follow-up, the mean spherical equivalent was -0.02 D for distance and -2.25 D for near vision. Of these patients, 97.4% achieved UCVA of 20/30 or better for distance and J2 or better for near, and 90% achieved intermediate vision (at 0.67 m) of J3.

Although stereo acuity was reduced in 81.6% of patients, almost all patients (97.3%) reported being satisfied or very satisfied with the procedure, and 92.1% reported being spectacle independent after surgery. Moreover, there was no compromise in the image quality because of the aspheric monofocal optics. Although, the spherical monofocal optical zone may also be used with similar results.

This technique can also be used with toric IOLs in patients with corneal astigmatism of more than 1.00 D who are not good candidates for a conventional monofocal IOL without requiring enhancement (Marques FF, Marques DMV. Pseudophakic monovision technique with toric IOL; unpublished data).

A second option to provide spectacle freedom after RLE is the use of bi- or multifocal IOLs, also known as pseudoaccommodating IOLs because they provide more than one focal point without any movement the IOL optic. Bifocal IOLs provide near and far vision correction by creating one focal point on the retina for distance vision and a second one before the retina for near vision using diffractive technology (Tecnis Multifocal ZM900; Advanced Medical Optics, Inc., Santa Ana, California) or combining refractive and diffractive technologies on the same platform (AcrySof Restor; Alcon Laboratories, Inc., Fort Worth, Texas). Multifocal IOLs produce distance, near, and intermediate vision with multiple focal points using zonal refractive technology (ReZoom; Advanced Medical Optics, Inc.).

These pseudoaccommodating IOLs provide a better range of visual acuity from distance to near vision in each eye separately, which might be useful in monocular patients as well as in patients with a previous monofocal IOL implanted on the first operated eye.6 Moreover, spectacle independence after surgery with these technologies is becoming more predictable. Nevertheless, the image created by the optics of these types with monofocal optics. They also create unwanted images (dysphotopsia), more severely than momofocal IOLs, such as glare and halos. Dysphotopsia is more likely to occur in scotopic conditions and limits some activities, such as night driving.7,8

The third and last option for RLE combines the advantages of the uniform surface of monofocal implants, providing a sharp image without the dysphotopsia seen with bi- and multifocal platforms, with the ability to provide good near, intermediate, and distance visual acuity. This combination is created in accommodating IOLs by the anterior movement of the implant during pseudophakic accommodation.

At least two IOLs are currently marketed as accommodating IOLs: the Eyeonics Crystalens AT-45 (Bausch & Lomb, Rochester, New York) and the 1CU (HumanOptics AG, Erlangen, Germany). Studies of these lenses with longer follow-ups have, however, demonstrated a reduction of accommodation affecting near vision.9,10 This is in part due to capsular opacification and fibrosis reducing the original elasticity of the capsular bag. The bag's axial length and volume decrease considerably after removal of the crystalline and implantation of the IOL.

More recently, an accommodating dual-optic IOL, the Synchrony (Visiogen, Irvine, California), was developed with the idea of simulating the filled capsular bag. This IOL has shown promising early results.11

When performing RLE, it is important to consider patient expectations. Unlike our cataract patients, these individuals have good-quality preoperative BCVA. In many countries, RLE is considered experimental surgery, so the surgeon must spend extra chair time to answer all questions, and adequate informed consent must be provided. It is also important to mention the possibility of need for enhancements after surgery to correct any undesired residual refractive error.

Demanding patients, those who have refractive errors of less than 1.00 D, or those who do not use eyeglasses for distance are the most difficult to please due to their good or acceptable preoperative uncorrected distance vision.

In conclusion, while surgeons wait for the introduction of an ideal IOL that provides good visual acuity in all ranges without compromising image quality and without loss of effect over time, we still have good options to offer our patients to fill their visual needs after a thorough and systematic examination.

Frederico F. Marques, MD, PhD, is a is a Medical Director of the Marques Eye Institute and Surgeon Assistants at the Institute of Cataract, UNIFESP, Sao Paulo, Brazil. He states that he has no financial interest in the products or companies mentioned. Dr. Marques may be reached at tel: +55 11 5677 3513; e-mail: fredani2010@hotmail.com.

Daniela M.V. Marques, MD, is a is a Medical Director of the Marques Eye Institute and Surgeon Assistants at the Institute of Cataract, UNIFESP, Sao Paulo, Brazil. She states that she has no financial interest in the products or companies mentioned. Dr. Marques may be reached at tel: +55 11 5677 3513; e-mail: fredani2010@hotmail.com.