The latest model IOLs: What do they offer us?

This month we take a look at the latest IOLs to enter the market and how they will affect our practices.

ByJorge L. Alió del Barrio, MD, PhD

Jorge L. Alió

The IOL industry has been providing us with a number of innovations that are now crowding the scientific programs of meetings worldwide, creating pressure on surgeons and high expectations among both surgeons and patients. The question is: What do they offer to the up-to-date and constantly evolving cataract lens surgeon?

There are currently three groups of lenses to be considered: presbyopic lenses, new IOLs with aspheric optical profiles and yellow ultraviolet absorbing IOLs.

Presbyopic IOLs can be either multifocal, partially accommodative or accommodative. Real accommodation means a change in the lens power related to active ciliary body action. A simple change in the optical power of the eye without IOL power change (such as happens in IOLs that are changing their position in the axis of the eye) should be termed partially accommodative.

Accommodative IOLs

Accommodative lenses are still the holy grail in the restoration of accommodation. Dual system lenses, such as the Sefarazi (Bausch & Lomb) and Synchrony (Visiogen) lenses, both relate their accommodative power to the change in position of one of the optics (the anterior one in most cases), when placed inside the capsular bag. The entire dual lens system functions as a unique optical system. Their action can be affected in part by the capsular bag retraction. These lenses seem to be able to restore accommodation within 1 and 3 days of implantation, and their long-standing effects are still under investigation.

Partially accommodative IOLs

Partially accommodative lenses, such as eyeonics’ crystalens, Human-Optics’ 1CU , Lenstec’s Tetraflex and Tekia’s TekClear, base their action on anterior posterior movement of the IOL related to ciliary body action. Multiple factors may influence this effect, and there is an important controversy as to whether these lenses really behave only by displacement or whether they experience changes in their optical configuration related to such cilary body action. These lenses may restore from 0 D to 1.5 D of accommodation, and their controversial variability has been an object of an important debate.

The paradigm of presbyopic IOLs eventually will be lenses that can restore accommodation over 3 D and, especially, if they are not related to the intercapsular situation, such as the NuLens (NuLens Ltd.). Such “real” accommodative IOLs jointly with lens refilling are the object of important investigations right now, and they will most likely offer the true solution to pseudophakic presbyopia within the next 5 years.

Multifocal IOLs

Multifocal lenses, whether refractive, diffractive or hybrid (diffractive central optic plus a midperipheral and peripheral refractive optic), create a division of light on two or more foci that increase the depth of field. Optical multifocality has been successfully demonstrated to restore near vision in the pseudophakic eye. They are controversial because neuroprocessing by the patient is involved, which affects their performance as well as tolerance by the patient. They may provide excellent results or unhappy patients and surgeons. The art of being a surgeon is tested here by the capability of the surgeon to detect those patients in which this indication is correctly related to the many factors that influence their performance and tolerance when implanted inside the human eye.

Aspheric IOLs

Aspheric IOLs are another important debate subject. For a long time, aspheric profiles have been the gold standard in optics in photography and telescopes, but despite their many advantages for human optics, they have not been introduced into the surgical practice until recently. They can be classified as neutral (creating no aspherical aberration, leaving only the natural aberrations of the eye, such as the Baush & Lomb Akreos); inducing moderate negative asphericity intraoculary (such as the Alcon IQ); or creating a negative asphericity inside the eye to compensate the positive aspherical aberration of the cornea, creating global asphericity, which aims to improve performance in the human eye (Tecnis, AMO).

In theory, negative asphericity in the optical system of the eye would lead to an increase in contrast sensitivity. However, in real practice such lenses are affected by any tilting or decentration that occurs to the IOL following surgery. The more negative asphericity they have, the more prone they are to losing their optical aspheric capabilities related to tilting.

Neuroprocessing studies have demonstrated that if they are within normal levels, the natural aberrations of the eye should be left alone because our brain has adapted to these optical conditions and behaves better than when these normal aberrations are changed. Other studies have claimed to increase the contrast sensitivity function with highly negative asphericity lenses. In practical terms, neutral asphericity IOLs seem to be most logical to me under normal conditions.

UV-blocking lenses

Last, but not least, prevention of age-related macular degeneration, a universal plague in the West, has brought about the introduction in the market of the yellow UV-blocking lenses. The controversy over these lenses is that they filter not only the UV but also the violet light. Scotopic visual function and chromatic perception should be affected by this. In real practice, it seems that neither of these issues are being observed in patients implanted with such chromatic absorbed lenses, most probably because neural processing balances the situation despite of the lack of violet light. However, it will be difficult to demonstrate practically the effectiveness of such lenses due to the multifactorial issues involved in the pathogenesis of AMD, the genetic background of this disease and the long-term process that involves the development of age-related retinal changes.

Bottom line

What can the clinician facing this huge amount of innovations do today? From my point of view, presbyopic lenses are led by optical multifocality. Diffractive IOLs offer a better optical system, and generally the hybrid models should bring the best clinical results. Intermediate accommodative lenses should be selected only when intermediate vision is targeted for improvement and near vision is of secondary importance. The potential for real accommodative lenses must improve in the immediate future in order to be introduced in human clinical use.

Concerning aspheric lenses, my position is to use those with neutral asphericity. I believe that leaving the natural aberrations of the eye within normal levels is the way to go. These lenses are less influenced by IOL decentration and tilt, two issues which are impossible to predict during surgery. Yellow lenses should be used in cases in which a background of age-related macular degeneration is evident in the patient and in cases in which macular problems are present such as diabetic retinopathy or retinal dystrophies.

We welcome all these innovations from the industry but we should maintain a guarded opinion about the real practicality and the cost benefit ratio they offer in the benefit of our patients.

For more information:

Jorge L. Alió, MD, PhD, can be reached at Vissum, Instituto Oftalmológico de Alicante, Avda de Denia, s/n, 02016 Alicante, Spain; +34-965-150-025; fax: +34-965-151-501; e-mail: jlalio@vissum.com. Ocular Surgery News could not confirm whether Dr. Alió has a direct financial interest in the products mentioned in this article or if he is a paid consultant for any companies mentioned.