Life behind the lens
Research honing in on PCO prevention through new surgical techniques and innovative lens design
David Spalton MD, FRCS
New IOL designs and surgical techniques suggest that there is the prospect of longer-lasting prevention of posterior capsule opacification (PCO) and include platforms that are likely to be amenable to the restoration of accommodation, said David Spalton MD, FRCS, in his HSIOIRS Kelman Award Lecture, which he delivered at the 23rd ESCRS Winter Meeting in Athens, Greece.
“I think we are going to see new intraocular lens designs which will modulate and control PCO. The open-bag concept has the possibility to leave us with a flexible bag in which we can place an accommodative lens,” said Prof Spalton, St Thomas’ Hospital, London, UK.
Prof Spalton noted that much of his clinical research has concerned the study of PCO. In the early 1990s, he and his associates developed a system at St Thomas’ Hospital for detecting and quantifying PCO. The project involved designing a special, state-of-the-art retroillumination camera and developing a software program based on texture analysis, which initially had been developed for military imaging analysis to quantify the area of PCO behind the IOL optic.
In 1994, Ekehard Mehdorn MD, Germany, reported his observation that eyes with Acrysof IOLs had a very low incidence of PCO. A subsequent study carried out by Prof Spalton and his team using their PCO analysis system confirmed Dr Mehdorn’s observation, showing that there was less PCO with the Acrysof lens compared to a similar silicone or PMMA lens. The reason for this was unknown until later research by Okihiro Nishi MD, Japan, demonstrated that it was the IOL’s square-edge that reduced PCO rather than the lens material. However, with time and longer follow-up it has become apparent that square-edged lenses delay but don’t prevent, PCO.
There are now a range of approaches currently under investigation for preventing PCO in a more long-lasting manner, which include new surgical techniques and IOL designs. Most have their caveats and all will inevitably require long follow-up.
Rupert Menapace MD, PhD, Austria, has proposed “button-holing” the IOL optic behind a posterior capsulotomy. Although this is very effective in preventing PCO, many cataract surgeons are reluctant to open the posterior capsule, Prof Spalton said.
Meanwhile, Burkhard Dick MD has proposed using the femtosecond laser to perform a posterior capsulorhexis at the end of a cataract procedure. Prof Spalton noted initial results are encouraging but pointed out that Albert Galand MD, Belgium, had used a posterior rhexis in the 1990s with ECCE to prevent PCO, but found that over time lens epithelial cells migrated over the surface of the anterior hyaloid and abandoned the technique.
Another approach is to prevent epithelial cells from proliferating by sandwiching the posterior capsule to the posterior lens surface – the ‘no space no cells’ concept. In their Vivinex IOLs, Hoya seek to achieve this through an ozone treatment of the posterior surface of the optic, rendering it more adhesive to lens epithelial cells. Animal studies look good, but clinical studies with the lens have so far not demonstrated any superiority over the Acrysof lens in terms of PCO prevention.
Prof Spalton said longer-term follow-up is needed to see whether clinical results can confirm the animal work.
The newest approach includes techniques that aim to prevent PCO by maintaining a separation between the anterior and posterior capsules, Prof Spalton said, originating from the fortuitous observation that eyes with the Synchrony accommodative lens remained remarkably free of PCO. The likely explanation for the PCO-preventive effect of this lens is that by preventing the anterior and posterior capsular leaves from sealing together, aqueous can irrigate through the capsular bag and wash out growth factors and cytokines, he noted.
Several new IOL designs aiming to exploit this principle are now under investigation. They include systems where the IOL is implanted within an endocapsular ring that maintains capsular separation. There is also a lens from AnewOptic Inc, which has a circular disc haptic designed to separate the anterior and posterior capsule, which is now entering clinical trials.
The open-bag concept has particular appeal in that it may provide a capsular bag free of PCO that maintains its flexibility for the newer types of lens that achieve accommodation through change of curvature. Examples of such lenses now in clinical trials include Powervision’s Fluidvision IOL and Lensgen’s Juvenal IOL.
Prof Spalton is a stockholder in AnewOptic Inc.
David Spalton: firstname.lastname@example.org