Why Apodized Diffractive-Refractive is Attractive

The evolution and application of an apodized diffractive-refractive multifocal intraocular lens

Robert Montés-Micó | 02/12/2015

There are many refractive principles that underpin a range of multifocal IOL designs
Apodized refractive-diffractive IOL designs can give implanted patients more light to near when pupils are small, and more light to far when pupils are large
The multifocal IOL that’s most widely studied is Alcon’s AcrySof ReSTOR, launched almost a decade ago
Here, a number of cataract/refractive surgeons discuss their experience with the lens

Patients’ visual performance after cataract surgery is determined by a number of factors: concomitant ocular comorbidities, quality of capsulorhexis, intraocular lens (IOL) positioning, but one of the biggest factors is the type of IOL implanted. Monofocal IOLs provide excellent visual function but, in many cases, their limited depth of focus means patients won’t have clear vision at both near and far distances. Growing demand by patients undergoing cataract surgery for satisfactory spectacle-free near and distance vision drove the development of multifocal IOLs (mIOLs).

The first multifocal IOL was three-piece, convexo-concave design, introduced in 1987 by 3M, however, the company stopped all IOL production in 1992. The first FDA-approved multifocal IOL in the United States was AMO’s Array in 1997, and this was replaced in 2004 by the ReZoom IOL. Today, many mIOLs are on the market; they can be classified in general terms as either diffractive or refractive. One notable IOL is Alcon’s AcrySof ReSTOR. It’s a bifocal IOL, first approved in the USA in 2005, and was the first to combine all three of the following optical concepts into its design: diffractive, refractive, and apodized. The latter term is important: it reflects the fact that the optical properties of the lens change across the optical surface from the center to the periphery. What it means in practice is that apodized diffractive optics make more light available to near when a patient’s pupil is small, and to distance when their pupil is larger, which means that it increases the proportion of light available for the most appropriate activity – near work in brighter light, and distant work in dimmer light, and consequently reducing the intensity of the ‘other’ light. A good example would be driving at night: a greater proportion of light would be directed to distant focus, and correspondingly, less light to the near focus, reducing the occurrence of glare and halo. As ReSTOR is the most widely studied lens in the literature, I interviewed several surgeons with extensive experience with mIOL implantation (and this lens design in particular) about their experiences.

Luis Fernández-Vega, University of Oviedo, and Fernández-Vega
Ophthalmological Institute, Oviedo, Spain.

I’ve implanted lenses from the ReSTOR family for over a decade, and look back on the first launch at the time as a landmark event. With the introduction came the possibility of easily and safely implanting a mIOL, correcting presbyopia and providing good outcomes. The number of cataract surgeries performed with mIOLs rose as a result and with it, the number of ReStor implantations, which gained market leader status.

The lenses are made of what the manufacturers call AcrySof: an acrylate/methacrylate copolymer, which makes the lens foldable, enabling smaller incisions than we were previously accustomed to and producing less surgically-induced astigmatism. Thus the patients eligible for treatment with mIOL technology increased. As the models evolved, the need for lenses with an aspheric design became evident. Patients started to report intermediate-vision problems, and it soon became clear that the lens’ visual performance was highly dependent on the patient’s pupil. Moreover, some additional problems were encountered – like the presence of halos and the need to use artificial light for reading. As a result, a new model of aspheric lens was designed, which improved patients’ intermediate vision and decreased reports of visual aberrations. This newer ReSTOR design has now made it possible for us to treat hyperopic patients with small pupils.

José Alfonso, University of Oviedo, and Fernández-Vega Ophthalmological Institute, Oviedo, Spain.

When I see hyperopic patients with cataract who are aged 70 years or older, I always consider implanting the +3 D aspheric ReSTOR. I believe that the pupil is a determining factor for the lens’ performance – if the lens is to be successfully implanted, the pupil size should range from 2.75 to 4.75 mm. I view the +2.50 D model as an advanced monofocal lens for patients with cataracts, as I think it provides a bit of added value to the patient in the form of improved visual performance, while still giving them contrast sensitivity that’s similar to that achieved with an ordinary monofocal lens. The ideal lens in my mind, would be a diffractive one, either bifocal or trifocal, depending on the needs of the patient, foldable, to minimize incision size, with a design that combats posterior capsule opacification (PCO). It has to be borne in mind that the combination of a bifocal lens and a small pupil may lead to increased depth of field and, consequently, to better near and intermediate vision. Having said that, an alternative approach could be to develop an apodized lens with several foci, so that the patient’s pupil-size range would not be a determining factor for post-implant visual outcomes. However, it’s important to remember that the lens’ toricity and asphericity features must be tailored to the patient’s characteristics – appropriate lens selection is crucial for ensuring happy patients with good vision after surgery.

Javier Mendicute, Donostia Hospital and Begitek Clinicas Oftalmológicas, San Sebastián, Spain.

I feel that the launch of ReSTOR represented a turning point in cataract and refractive surgery. It opened up a field that hadn’t existed before – these foldable, apodized IOLs could be used to correct presbyopia as part of either cataract surgery or refractive lens exchange (RLE). Given the refinements made to the AcrySof range over time, in particular in terms of haptic stability and centering of the IOL – which were carried over to the ReSTOR model – surgeons had confidence in the stability of the implanted lens and the predictability of outcomes. RLE patients have high demands – they expect significantly improved, post-surgical, spectacle-free vision from their premium procedure – this has spurred the evolution of the IOL’s design, and surgical procedure, the aim being to achieve emmetropia. Naturally, patients undergoing cataract surgery have benefited greatly as a result. In particular, the impact has been greater in my hyperopic patients and those with lower refractive errors, as visual outcomes after surgery have been very good. PCO remains a concern. And though the incidence with ReSTOR lenses is low, if it does occur, it could be a big problem – levels of PCO that would be visually insignificant in patients with monofocal IOLs, can wreak havoc in patients diffractive multifocal IOLs.

Ramón Ruíz-Mesa, OFTALVIST C.I.O (Clínica Jerez), Jerez de la Frontera, Spain.

I have implanted many IOLs over the years, and I believe that the ReSTOR lens shows good refractive stability. As I’ve learned from my experience with monofocal toric IOLs, high stability and predictability are central for achieving astigmatism correction – and those are important considerations when patients choose the right mIOL for them.

Luis Cadarso, Hospital Meixoeiro and Clínica Cadarso, Vigo, Spain.

Multifocal lenses require a great deal of expertise from the surgeon. I believe that a great amount of emphasis has been put on lenses and their design and little on other aspects that require high levels of skill to achieve the best possible outcome, such as:

• performing a correct biometric evaluation,
• accurately measuring all the required parameters for lens power calculation,
• choosing the most appropriate formula for each particular patient and,
• continuing professional development.

It’s critical that surgeons cover all basis when it comes to their technique before moving to the next stage of lens selection. When ultimately deciding on a particular lens type, be it monofocal or multifocal, the choice must be based principally on which lens will leave the patient most satisfied.

Laureano Álvarez de Rementería, Clínica Rementería, Madrid, Spain.

Data acquired over the decade since the AcrySof ReStor IOL was launched have shown it to have excellent rotational stability – in most cases, lens rotation is less than 5° – making it a good choice for presbyopia correction in astigmatic patients. When it comes to toric lenses, I think they can be improved with small design changes, like making the tiny reference marks on the IOL more visible to the surgeon. Other features that would be nice to have is the availability of lenses preloaded into injectors, lenses than can be inserted with the minimal incision size possible, and eventually, a truly accommodative IOL.

Elena Barraquer, Centro de Oftalmología Barraquer, Barcelona, Spain.

The visual performance of the ReSTOR family of IOLs is similar to that of other multifocal IOLs – patients who choose to have multifocal lens implants will obtain in most cases, independence from glasses. A few will need them, but only occasionally. IOLs that employ hybrid designs; different add power, asphericity, toricity and apodization – like ReSTOR – have yielded excellent results and opened up realistic opportunities for the effective correction of vision in patients with presbyopia and/ or astigmatism. Patients always want to have the best possible vision after cataract surgery or RLE, so the constant challenge is to produce ever-better IOLs that meet that demand. Thanks to the advances made over recent years, we now have a portfolio of options to suit even the more demanding patient.

Robert Montés-Micó is a professor in the Department of Optometry and Vision Sciences in the School of Physics at the University of Valencia, with research interests in accommodation and myopia, contact lenses and the tear film, and the aging eye.