What elements are needed in accommodating IOL designs to make them successful ?

eduardo F. marques, md Based on my experience, there are five essential elements in successful accommodating IOL designs, as outlined below. No. 1: Allow spectacle independence for all distances. A successful accommodating IOL should provide enough pseudophakic accommodation to allow spectacle independence for all distances. This can be achieved using one or a combination of the two physiologic changes that also occur in the natural lens with contraction of the ciliary muscle: • Increase in paraxial power of the IOL. This is the mechanism used in the Synchrony dual-optic accommodating IOL (Abbott Medical Optics), which changes the relative distance between the IOL’s two optics with ciliary muscle contraction, thus increasing paraxial power and providing intermediate and near focus. This mechanism has been demonstrated objectively in patients up to 4 years after implantation of the IOL. It was also one of the mechanisms of action suggested for the Crystalens accommodating IOL (Bausch + Lomb), which is believed to move anteriorly with contraction of the ciliary body, although this is controversial. • Increase in anterior curvature of the IOL. Some believe this is the mechanism of action of the Crystalens, which may change shape due to its flexible material. Additionally, the second generation of the dual-optic accommodating IOL (Synchrony Vu) includes a central area of negative spherical aberration on the surface of the anterior optic to try to mimic the changes occurring in the natural lens during ciliary body contraction. In theory, this change allows a gain of 1.00 D depth of focus for near. No. 2: Guarantee the same optical quality as a monofocal IOL. The main advantage of accommodating IOLs is the lower incidence of the dysphotopsia and loss of contrast sensitivity that are typical of multifocal IOLs. This is due to the use of monofocal optics, a trait that all available accommodating IOLs have in common. No. 3: Afford excellent refractive predictability. One of the criticisms regarding existing accommodating IOLs is their lower refractive predictability compared with multifocal IOLs. Stability and final position of an accommodating IOL depends largely on the size and shape of the patient’s capsular bag and on contraction and fibrosis of the bag, which interfere with the refractive result. The design of accommodating IOLs should provide good stability and adaptation to the bag, allowing precise IOL power calculation. No. 4: Allow easy, safe implantation through a small incision. Small incisions induce less astigmatism, allow quicker recovery, and provide increased safety compared with larger incisions. One of the difficulties with accommodating IOLs has been the need for larger incisions to implant these more complex devices. No. 5: Prevent posterior capsular opacification (PCO). Prevention of PCO is an essential characteristic of a successful IOL. The rate of PCO is lower with dual-optic IOLs than with single-optic, probably due to the maintenance of an open system, allowing circulation of aqueous in the capsular bag. Other strategies include the more common use of a square optic edge.