Introducing a new IOL

March 1, 2006

New technologies, advances in phacoemulsification and better instruments have improved outcomes and reduced complications in cataract surgery. However, a similar advance has not been achieved in the same manner with intraocular lens (IOL) development.

What's the problem?

As we all know, it will take time for evidence-based studies to settle this most controversial question. In the meantime, we clinicians require practical advice to share with our patients when discussing risk-benefits and alternatives. We have many options open to us; unfortunately, these options have not been able to fully meet our needs. For example, the introduction of the AcrySof lens, made of a very promising hydrophobic material, but with a biconvex design with increased curve in its posterior face compared to the anterior. This lens has been linked with reflex stimulation and vision quality impairment. In addition, multifocal lenses are problematic in terms of night-time glare, halos and decreased contrast sensitivity, which has led to the recent idea of improving the pseudophakic wavefront. The aspheric geometries show great efficiency in laboratory studies, under steady conditions, however, when decentred or tilted, as could occur after bag implantation, optic quality features (MTF) are reduced to a higher degree than with standard geometries. Similar outcomes are observed with lenses designed for implantation through small incisions, (up to 1 mm). These lenses showed great instability in the capsular bag because of their small size and thickness. In addition, the behavioural mechanisms of pseudoaccommodative lenses are not clear and their efficiency to correct presbyopia is no more than 1 D.

Answering the brief: it's a balancing act

Consequently, it is important that we look for a better balance between safety and efficiency. Following this approach, our purpose was to find a lens made of a suitable material and with optic and haptic zones designed such that a balance between vision quality, biocompatibility and the ability to implant through the smallest incision could be achieved.

As a result, we have designed a lens made of hydrophilic acrylic material of low water content and selective polymerization that offers good biocompatibility and the possibility to modify its hardness degree in every zone of the lens. This permits easier folding of the lens for implantation through an incision of 1.8–2 mm. At the same time, the lens has good stability in the capsular bag avoiding decentration and tilting effects. The latter feature results from both the positioning of the lens in a very posterior location pressing against the posterior capsule, and the design and hardness level of the haptics, which absorb uneven bag retraction.

The square edges of the lens, optic and haptic zones were designed to control capsular opacification, together with the pressure against the posterior capsule. In addition, the posterior location of the lens provides a very important optical advantage because it is placed on the nodal planes of the eye equating to better vision quality, no image magnification phenomena, and greater tolerance of decentration and tilting effects.