New lenses

Despite improvements in recent years, multifocal intraocular lenses (IOLs) will never provide a silver bullet solution to presbyopia, Jorge L Alió MD, PhD told delegates attending the 2015 Congress of the European Society of Ophthalmology (SOE) in Vienna, Austria.

“The latest generation of multifocal IOLs offers a real improvement on earlier iterations of the technology with better range of foci, less loss of contrast sensitivity function, fewer issues with halos and glare and better patient satisfaction,” he said.

Nevertheless, despite these advances Dr Alió believes that multifocal lenses will ultimately come to be supplanted by accommodative IOLs.

“We need to bear in mind that multifocal IOLs are not physiological and they will always require some degree of neuroadaptation. Once accommodative IOLs are developed adequately, multifocal IOLs will be unable to compete as happened in the past with pseudophakic glasses and IOLs,” said Dr Alió, of Vissum Ophthalmologic Institute, Alicante, Spain.

LIMITED ENERGY

By definition, multifocal IOLs divide light into different foci, with limited energy available for each focal point, said Dr Alió. The overlapping of different foci is neither physiological nor normal in the evolution of humans or animals, he noted, and therefore the brain is required to adapt to the changes induced in the quality of the retinal image caused by the dispersion of light. Another challenge facing multifocal IOLs is the superposition of images causing glare and halos, although modifications in lens design have gone some way towards addressing these concerns, said Dr Alió.

Dr Alió said that the latest generation of extended depth-of-focus IOLs were a clear improvement on earlier multifocal designs.

The Tecnis Symfony extended depth of vision IOL (Abbott Medical Optics), for instance, uses three principal optical strategies to achieve optimal visual quality for the patient: a proprietary diffractive echelette design to elongate the focus of the eye and deliver an extended range of vision; achromatic technology to reduce chromatic aberration and enhance contrast sensitivity; and, finally, spherical aberration control.

Such improvements, however, will not be sufficient to enable multifocal IOLs to compete with the next generation of accommodative IOLs, said Dr Alió.

Accommodative IOLs seek to induce a progressive change in the power of the lens related to active ciliary body action, thereby mimicking the natural physiological process of accommodation that is lost as we get older, said Dr Alió.

IOL manufacturers have adopted three basic approaches to try to replicate the process of accommodation, he explained: inducing a change in axial position with a single or dual optic, a change in shape or curvature drawing on capsular bag elasticity, the zonular-capsular diaphragm and changes in vitreous-capsular pressure, or a change in refractive index or power.

Of the newer accommodating IOLs, Dr Alió said that two of them – FluidVision (PowerVision) and Sapphire (Elenza) – are designed for capsular bag placement and two – DynaCurve (NuLens) and Lumina (Akkolens/Oculentis) – are meant for sulcus placement.

CAPSULAR BAG

Dr Alió said that the capsular bag seems to be an inadequate location for accommodating IOLs, mainly due to the fibrosis and atrophy that occur after crystalline lens removal.

“The capsular bag is the basal membrane of the lens epithelium. Once the crystalline lens has been removed, it no longer has any reason to exist. With no function and no anatomy to support, fibrosis and atrophy are unavoidable and the capsular bag cannot function in the long term when it has been emptied,” he said.

By contrast, the forces that continue to be generated by the zonular-capsular system suggest that this might be a more viable location for accommodating IOL designs, he said.

A pilot study of the Lumina varifocal lens seems to confirm the accommodative potential of this sulcus-implanted IOL, said Dr Alió.

The lens was implanted in 51 eyes and compared to a monofocal control lens in 22 eyes (AcrySof ResTor, Alcon). Objective measurements with the WAM-5500 (Grand Seiko) and defocus curves showed that the Lumina successfully restored variable amounts of astigmatism and provides accommodative performance in the range of 1.50D to 6.00D.

Jorge L Alió: jlalio@vissum.com