CHANGE OF FOCUS

An IOL with a three-layered optic that is responsive to the eye’s physiological accommodative mechanisms could, in theory, provide cataract patients and presbyopes with a wide range of focusing powers, said Pablo Artal PhD, Laboratorio de Optica, Universidad de Murcia, Spain. “Although different accommodative IOLs have been proposed, the current designs only provide a rather modest range of accommodation in the best cases. We are proposing a new triplet optical design which could in theory provide a wide range of potential accommodation and which could be incorporated into an IOL,” Dr Artal told the XXXI Congress of the ESCRS in Amsterdam.

Dr Artal noted that accommodating IOLs are based on the use of the eye’s natural physiological accommodation apparatus to exert a force that will induce changes in an IOL’s optical power. However, current designs, which work by the forward and backward movement of the IOL’s optic, or optics, are limited to changes in focus of a few dioptres.

In the new lens design Dr Artal and his associate Dr Josua Fernandez are proposing, accommodation depends on changes in convexity in the optic such as occur in the crystalline lens with natural accommodation. Only very small amounts of change in an optic's convexity are necessary to achieve a broad range of focusing power.

The lens design consists of three layers composed of silicone and acrylic materials. Its equatorial diameter and therefore its convexity is sensitive to small amounts of compression. There are currently three designs that the Murcia team has assessed on a theoretical basis. Each design differs in its responsiveness to compression forces based on differences in the thickness and dimensions of each layer.

“The triplet-like optical structure we propose can produce gains high as one dioptre per micron of equatorial compression allowing for large range of power changes. The proposed triplet-lens also permits the incorporation of aspheric or toric surfaces for optimising ocular spherical aberration or correcting astigmatism. Chromatic aberration and ghost images analysis shows a similar performance to monofocal standard IOLs, Dr Artal said.

The triplet optic will typically have a central thickness of 1.0mm and an optical zone 6.0mm in diameter. Those geometrical dimensions and the structure of the proposed haptics could allow implantation of the lens through a conventional corneal incision of 2.0-3.0mm in diameter. Dr Artal and his associates are also in the process of devising a special intracapsular ring to accurately control the accommodative IOL’s equatorial diameter in response to accommodative effort.

“An intraocular triplet lens with a wide variable power as a response to small compression forces has been designed. This new lens, in combination with a capsular ring for the precise control of its equatorial diameter, may provide a large range of accommodation restoration,” he concluded.

Pablo Artal: pablo@um.es