Are all square-edged lenses equally square?

September 1, 2008

Dr Liliana Werner believes that it is the shape of an IOL edge, rather than the material from which it is made, that determines the likelihood of PCO.

Key Points

With regards to the surgical technique, there are three important steps that must be applied to help prevent PCO: 1) thorough cortical clean-up and copious hydrodissection; 2) in-the-bag IOL implantation to avoid asymmetric fixations; 3) a capsulorhexis that is a little smaller than the diameter of the optic of the IOL, so that a small part of the anterior capsule is available to overlap the periphery of the IOL optic, thus creating a "shrink-wrap" effect.

Techniques under investigation

In addition, we are evaluating a laser system (PhotoLysis system; A.R.C. Laser) that creates pulses and wave shocks to help detach the remaining lens epithelial cells from the bag after the phacoemulsification procedure.

We are also testing some other interesting devices, such as a small loop device that we insert under the anterior capsule after capsulorhexis (EpiLoop; PhacoTreat). When we increase the size of the loop, the loop completely surrounds the capsular bag and dissects the capsular bag from its contents.

IOLs: three factors influence PCO rate

In addition to surgical technique, three factors related to IOLs also influence the incidence of PCO following cataract surgery. Specifically the material, the edge and the optic-haptic angulation of the lens are all important factors that must be considered.

With regards to the material of the IOL, Dr Reijo Linnola of Finland originally proposed the "sandwich theory", which was evaluated on studies conducted in cadaver eyes implanted with different IOLs at Medical University of South Carolina, US. 1 This theory suggests those lenses with a bioadhesive surface allow only a monolayer of lens epithelial cells to attach to the capsule and the IOL, thus preventing further cell proliferation and capsular bag opacification.

To test this theory, we performed two large immunohistochemical studies in post-mortem pseudophakic eyes. Specifically, we analyzed the proteins that were attached to the surface of the IOLs. We observed more fibronectin - a protein of adhesion - mediating the adhesion between the capsule and hydrophobic acrylic IOLs than with any other type of IOL. These results signify that not all IOL materials cause the same effects within the eye. I admit that this may have a more significant influence on anterior capsule opacification, because this complication depends on the contact between the capsule and the IOL. Nevertheless, the influence of lens material biocompatibility must be considered.

A second IOL design attribute that may help to prevent PCO is the incorporation of an optic-haptic angulation between the optic and the loops (generally in three-piece designs). This design feature enables the surgeon to push the IOL optic against the posterior capsule, thus enhancing contact between lens and capsule, which in turn enhances the barrier effect of the IOL optic.