POSTERIOR CAPSULE OPACIFICATION

Research to identify factors influencing posterior capsular opacification (PCO) has led to surgical techniques and IOL designs that have limited the development of this complication after cataract surgery. However, the problem of PCO has not been eliminated, and further study is needed to understand its true scope and the efficacy of novel strategies to prevent its occurrence, according to Oliver Findl MD. “Current data for otherwise healthy eyes implanted with modern IOLs show that Nd:YAG capsulotomy rates are only about three per cent at two to three years postoperatively. Still, longer follow-up to five years and beyond is needed because there is some evidence that PCO is increasing over time,” said Dr Findl, director, Vienna Institute for Research in Ocular Surgery, Hanusch Hospital, Vienna, Austria.

Speaking at the 26th Asia-Pacific Association of Cataract & Refractive Surgeons Annual Meeting, Dr Findl reviewed principles for PCO, which provides a basis for understanding how various factors limit or allow its development, and he discussed the effect of specific IOL features on PCO, including the relatively new idea that a design able to keep the bag open may be beneficial. Dr Findl explained that there are two types of lens epithelial cells (LECs) in the eye – anterior capsule LECs and equatorial LECs. The anterior capsule LECs, which transdifferentiate into myofibroblasts after surgery, modulate capsular fibrosis leading to capsular collapse, sealing of the anterior and posterior capsules and “shrink wrapping” of the optic. PCO develops when the equatorial LECs, which are regeneratory cells programmed to regrow the lens, are able to migrate behind the IOL.

IOL design factors

A sharp posterior optic edge that indents the posterior capsule and causes capsular bending provides an augmented mechanical barrier to LEC migration. This explains why PCO is seen less with sharp edge versus round edge IOLs, noted Dr Findl, reviewing results from a meta-analysis he conducted investigating interventions for preventing PCO [Cochrane Database Syst Rev 2010 Feb 17(2):CD003738]. “Ideally, the anterior and posterior capsules should be firmly sealed and there should be a good bend of the posterior capsule over the optic edge because months to years later, the regeneratory LECs will reopen the capsular bag if it is not permanently ‘glued’,” he said.

Haptic configuration may also play a role in PCO since it affects whether there is contact between the optic and the posterior capsule and also the quality of the posterior capsule bend. Even though single-piece IOLs are now available with a 360-degree square posterior optic edge, Dr Findl pointed out the haptic of these implants is relatively thick. This bulk may limit total fusion of the anterior and posterior capsules and thereby also interfere with complete shrink wrapping of the IOL optic and an optimal capsular bend.

Dr Findl noted that in the meta-analysis he conducted, PCO scores were not significantly different comparing singlepiece and three-piece IOLs. However, results from a clinical trial he conducted comparing the two implant styles showed a tendency for more PCO after three years in eyes implanted with the single-piece technology. “While there is no proof today, we believe that with longer follow-up, the single-piece IOLs may do worse,” said Dr Findl, who is also a consultant ophthalmic surgeon at Moorfields Eye Hospital, London, UK.

The effect of IOL material on PCO development also remains unclear. In the meta-analysis, hydrophilic acrylic IOLs had more PCO than implants made of hydrophobic acrylic or silicone. However, optic edge configuration may be a confounding factor in the outcomes because the hydrophilic acrylics included a mix of round- and sharp-edge IOLs. Furthermore, as a consequence of the production process, the sharp edge of hydrophilic acrylic IOLs remains somewhat round. “A modern hydrophilic material IOL with a sharp edge may have good performance for PCO risk. More time is needed to tell, and for now the jury is still out,” Dr Findl said.

Future strategies

The surprising finding of minimal PCO in eyes implanted with the dual optic accommodating IOL (Synchrony, Visiogen) has turned attention to the idea that keeping the capsular bag open may be useful. Further support for this concept comes from a study Dr Findl conducted of a prototype silicone IOL that kept the capsular bag open by virtue of its circular tripod design. He noted there was no evidence of PCO in patients followed to three years post-implantation. Currently, the explanation for these findings is unclear, but Dr Findl put forth a few ideas.

“An open capsular bag allows continuous flow of aqueous that may contain or remove factors affecting the development of PCO. In addition, this prototype IOL featured ring modules exerting pressure at the equator that may have prohibited proliferation of the regeneratory LECs.” Meanwhile research is continuing to identify effective strategies to prevent PCO by completely removing or destroying LECs during surgery. “The hope for the future is to refill the capsular bag with an injectable material after the crystalline lens is removed. However, the viability of this approach depends on eliminating PCO,” Dr Findl told EuroTimes. “Unfortunately, nothing available now or on the horizon appears capable of doing this job.”