The rising demand for presbyopia-correcting IOLs has led to a rise in patient expectations, but can we please everyone? questions Professor Jay Pepose.
Demand rising for presbyopia-correcting IOLs
This increase in demand has been prompted by a number of events, including the shift to outpatient surgery, improved patient outcomes, and changing demographics in many countries as their population ages. For example, in the US, a direct consequence of the "baby boom" that spanned between 1946 and 1964 is that someone turns 60 years old every eight seconds. The dramatic rise in births following World War II, from 2.8 to 3.4 million between 1945 and 1946 alone, now represents roughly 26% of the US population or around 76 million "baby boomers". This group has the necessary financial resources, motivation and information technology to seek out surgeons who are experienced in refractive cataract surgery or lens exchange, with the goal of reducing their dependence on glasses for near, intermediate and distance vision.
What are the options?
While more options are available in Europe, in the US there are currently three IOLs approved for the treatment of presbyopia and aphakia: Crystalens (Bausch & Lomb), ReZoom (AMO) and the single piece AcrySof ReSTOR apodized diffractive IOL (Alcon).
Crystalens is an accommodating IOL, available in a 4.5 or a 5 mm biconvex optic, manufactured from a third generation silicone material (Biosil), with flexible hinged plate haptics designed to allow movement and/or changes in shape of the lens optic in response to accommodative effort.
While currently the only FDA-approved accommodating IOL, it is likely that the increased near vision with this lens compared with a monofocal IOL may reflect both pseudoaccommodative and accommodating components, such as the optic location near the nodal point of the eye, accommodative arching (i.e. a change in optic shape during accommodative effort that creates a power gradient with more near power near the centre than the periphery), and spherical aberration. All of these components may be synergistic with some axial movement of the optic in enhancing near and intermediate vision and depth of field.
Another iteration of Crystalens under development is the Crystalens HD IOL, which incorporates a proprietary aspheric component onto the Crystalens 5-0 optic and, in initial clinical trials, enhanced the number of patients achieving J1 and J2 vision compared with the Crystalens 4.5 AT or the Crystalens
5-0. Unlike multifocal refractive or apodized IOLs, there is no splitting of light energy between multiple images or loss of light into higher diffraction orders with the Crystalens accommodating IOL.
The ReZoom IOL (AMO) is a second-generation, refractive multifocal lens comprised of hydrophobic acrylic material with angulated, modified "C" PMMA haptics. This distance dominated refractive lens has five concentric refractive zones alternating for distance and near vision, with aspheric transitions that allow for intermediate vision. The distribution of light with this lens is pupil size dependent, with more light directed at distance and intermediate foci with a 2 mm pupil, and about 30% to near and 10% to intermediate with a 5 mm pupil.