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NEW advances in the design of intraocular lenses and capsular tension rings as well as innovations in surgical techniques are helping to reduce the incidence of posterior capsule opacification (PCO) after cataract surgery. That was the upbeat assessment of a number of researchers who presented the latest clinical data and developments in the field of PCO prevention at the XXI ESCRS Congress. Posterior capsular opacification, which remains the most common postoperative complication for cataract surgery, is caused by residual, equatorial lens epithelial cells (LECs) migrating to the centre of the posterior capsule, resulting in significant visual symptoms.
All patients underwent phacoemulsification and lens removal by the same surgeon while under topical anaesthesia. Patients who had received the capsular tension rings had significantly lower incidences of PCO at three, six and 12 months and also at the two year mark, noted Dr Hehn. CTR results same with different IOL types He said it was particularly noteworthy that these results were obtained regardless of the type of IOL implanted, whether silicone, hydrophilic or hydrophobic acrylic. An analysis comparing treatment with and without capsular tension rings revealed some intriguing findings for the different IOL types.
When the CTR is in place inside the capsular bag it instantaneously exerts a 360° tangential tension on the posterior capsule, he added. Japanese specialist Okihiro Nishi MD shed further light on the critical question of whether IOL design is more important than lens material in preventing PCO. Dr Nishi remarked that the weight of clinical evidence now suggests that the introduction of sharp-edged lenses by several IOL manufacturers has probably been responsible in great part for the reduction in the incidence of PCO. The sharp edge helps prevent PCO by forming a barrier to prevent endothelial cells from migrating between the lens and the capsule and then reaching and covering the back of the optic. In a recent study, Dr Nishi and his team implanted five rabbits with silicone IOLs in one eye and acrylic IOLs in the contralateral eye. Both IOLs incorporated the sharp-edged design thought to inhibit LEC proliferation onto the optic surface. Three weeks after surgery, there was no substantial difference in PCO intensity between the two IOLs in the posterior view. Histopathological examinations revealed that a sharp bend was formed at the sharp optic edge of the posterior capsule with both IOLs, noted Dr Nishi. Optic edge the key factor Dr Nishi said that their research thus far indicated that if a discontinuous capsular bend is created by an IOL with sharp edges, the bend may induce contact inhibition of migrating LECs regardless of the material composition of the lens. While he didn't discount the material components of the IOL as having some role to play in preventing LEC migration, he noted that the main factor appears to be the formation of a discontinuous capsular bend to prevent PCO. "The sharp edge was effective in creating a sharp capsular bend which significantly prevents PCO, but the results did not show any role of IOL materials in PCO reduction. To investigate further, alternative methodologies should be considered," said Dr Nishi. David Apple, MD of the United States charted the impressive progress of PCO prevention methods since the 1980s – when YAG capsulotomy rates were in the 50%-plus range – to a situation today where he believed that consistent single-digit PCO rates were possible. He said that this was largely due to a combination of factors such as improved surgical techniques and IOL design. The surgeon-related factors include capsulorhexis to cover the entire optic edge, thorough cortical cleanup to the lens equator, and in-the-bag IOL fixation. He suggested a further improvement in reducing PCO might be obtained by tackling what he called the "Achilles' Heel" of some one-piece IOLs – the haptic-optic junction that his team's research suggests provides a platform for cell proliferation onto the IOL optic. Dr Apple said that this junction was the one place on the IOL where the square edge was absent and was thus a likely bridge for LEC migration. "The rounded edge configuration at these points on the IOL provides a possible route for the migration of lens epithelial cells onto the surface of the optic and could be the Achilles' Heel of these lenses in terms of reducing PCO", he said. The performance of a hydrophilic acrylic IOL may be improved by a design change with creation of a 360 degree square optic edge, noted Dr Apple. Dr Apple noted that Rayner has begun to incorporate these design changes with its CentreFlex range of acrylic one-piece IOLs. Frederic Hehn MD David J. Apple, MD,
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As well as causing the opacification of the optic, cell migration and subsequent development of fibrosis de-centres the lens and causes it to move within the capsule. Although PCO is generally easily treated with YAG laser capsulotomy, this procedure can be problematic, especially for certain IOL types. Known complications include severe IOL iatrogenic damage, significant IOL subluxation or dislocation, retinal detachment and secondary glaucoma. The key role of capsular tension ring (CTR) implantation in reducing PCO was discussed by French specialist Frederic Hehn MD, who conducted a prospective study in which 500 patients received capsular tension ring implants. 
At the two-year follow-up, only three percent of patients who had received a hydrophobic acrylic IOL together with the CTR required YAG capsulotomy, compared with 10% of those who received the same IOL but no ring – a statistically significant difference. Similarly, the YAG capsulotomy rate for those who received the hydrophilic acrylic Stabibag IOL and a CTR was only six percent, compared with 20% for those who did not receive a ring. YAG rates were four percent for those who received the silicone Si55 lenses with capsular rings, compared with 18% for those not receiving a ring. Dr Hehn noted that no patients who had received capsular tension rings required YAG laser capsulotomy during the first year of follow-up. This probably decreased the risk for subsequent retinal detachment, he said. Better centration was another apparent benefit of the capsular tension ring approach. This was observed in all types of IOLs used, particularly multifocal lenses. Poor centration has been a general problem with that type of lens in the past. 
The capsular tension ring may also be useful in the paediatric cataract setting, where PCO is a persistent problem. Dr Hehn described one case of a six-year-old cataract patient who remained free of PCO and did not require vitrectomy after 18 months of follow-up. "Our findings demonstrate that there is no contact inhibition of cells by an IOL with a discontinuous posterior edge. At the cellular scale of 10 microns, for a ‘fibroblast-like' LEC the IOL seems to be not at all smooth but rough and porous. Therefore, a sharp edge does not exert contact inhibition at a cellular level. Instead, it creates a tension effect which mechanically blocks LEC migration. Other researchers have demonstrated that a square-edged IOL design exerts twice as much pressure on the posterior capsule as does an optic with a round edge. This higher pressure is done at the ‘p point' contact between the corner of the edge and the posterior capsule."