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    Enhancing refractive lens exchange outcomes

    Minimizing spherical aberration with the Tecnis multifocal IOL


    Frank Goes, MD
    The main goal of every refractive and cataract surgeon is to see their patient walk out of the clinic having achieved a visual acuity of 20/20; however, even if this ideal state is achieved, patients may still complain of, amongst other things, halos, glare and night vision problems. These problems may still persist, even when visual acuity is at its optimal level, and this is largely attributable to a decline in contrast sensitivity, which inevitably leads to poor functional vision, hence inability to adequately perform certain tasks such as night-time driving.

    It has been suggested that loss of contrast sensitivity occurs as a patient ages and this, in turn, has been linked with changes in the spherical aberration of the human crystalline lens, which increasingly becomes positive as the human eye ages and can no longer compensate the already positive corneal spherical aberration. Because many IOLs marketed today do not accommodate the enhanced spherical aberration displayed by the aging crystalline lens, IOL implantation in older, cataract patients often fails to enhance vision to a level that is greater than that of the average non-cataractous lens of a similar age. As a consequence, the patient will still experience reduced visual quality.

    Since the late Sir Harold Ridley implanted the very first IOL in 1949, many have worked tirelessly to design the ultimate lens that will be free of tilt or decentration concerns, provide long-term, high quality vision and avoid complications such as posterior capsule opacification (PCO).

    Enter the new generation of multifocal lenses

    Figure 1: Refractive outcomes according to formula
    One such innovation in design and function is evident in the new generation of multifocal IOLs, the introduction of which has led to an increased interest in refractive lens exchange (RLE) for individuals above the age of 45 who do not have cataracts, but desire better vision without glasses. Furthermore, cataract surgery on a whole has become more "refractive" in nature as today's more active cataract patients increasingly demand better postoperative visual results. Surgeons must therefore begin acknowledging that a patient of presbyopic age wants more out of their lens implant and, in fact, even in the absence of a cataract, are becoming less inclined to accept the poor vision that comes with age, but instead wants an enhanced quality of life.

    Though still in its infancy, the market for refractive IOLs is predicted by many to rocket over the next few years, with more and more surgeons introducing these lenses into their clinical practice. This prediction has been further supported in the US by the recent CMS (Centres for Medicare and Medicaid Services) ruling which, having acknowledged the importance of this new generation of presbyopia-correcting lenses, granted Medicare patients the right to pay a premium to receive the implants.

    Traditionally, although proven to be effective in reducing spectacle dependency, multifocal IOLs have been plagued with reports of certain visual side effects, such as halos and less sharp vision. This stems from their failure to address the problem of spherical aberration.

    Only recently, however, has attention been placed on creating an IOL, which deviates from the original spherical design introduced by Ridley all those years ago. In a bid to address this unmet need, a modified prolate anterior surface IOL (Tecnis, AMO) has been developed and is now setting a new standard of visual performance in cataract surgery. It is also contributing to the rising interest in RLE.

    Introducing the Tecnis multifocal IOL

    CE-marked since 2004, the developers have added a diffractive multifocal optic to the posterior surface of the lens, resulting in the creation of the modified prolate multifocal Tecnis IOL. Instead of aggravating the problem of spherical aberration, as seen with spherical IOLs, the multifocal Tecnis lens actually neutralizes the spherical aberration of the average older cornea.


    Frank Goes, MD

    Frank Goes, MD is the Medical Director of the Goes Eye Centre Left Bank in Antwerp, Belgium. He may be reached by email: ...

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