PCO FORMATION

A number of new surgical and pharmacological approaches currently under investigation show promise in reducing the incidence of posterior capsule opacification (PCO) after cataract surgery, according to research presented at the XXXI Congress of the ESCRS in Amsterdam. PCO remains one of the most common complications of cataract surgery, despite advances in surgical techniques, intraocular lens materials and designs over recent years, according to Guy Kleinmann MD.

“PCO is still a problem after lens implantation and particularly in the case of so-called premium IOLs. However, we believe that our approach, which is to open the capsular bag instead of shrinking it, could reduce the rate even further,” he said. Dr Kleinmann, Kaplan Medical Centre, Rehovat, Israel, said that initial studies in rabbits and cadaver eyes have yielded encouraging results for the open bag device (CleaRing, Hanita Lenses), which is implanted in the capsular bag prior to IOL implantation.

“The ring, which is made of either hydrophilic or hydrophobic material, is placed in the capsular bag before the IOL implantation. The concept is that the ring acts as a support for the anterior capsule and creates a barrier to lens epithelial migration across the IOL optic. Implanting such a device also means that the surgeon is free to implant whatever lens they desire,” he said. The ring features several unique characteristics: 1. A special square-edge design; 2. A groove for IOL haptics fixation; 3. “Windows” which allow aqueous flow to the equator LECs; and 4. A “roof” for anterior capsule lifting and support.

In the phase I rabbit trial, the ring was tested in conjunction with two IOLs: the Tecnis (AMO) hydrophobic IOL and the SeeLens AF (Hanita Lenses) hydrophilic IOL. Both IOLs have a total diameter of 13.0mm, an optic diameter of 6.0mm and incorporate a 360 square-edge design. In the control group, six Tecnis and six SeeLens IOLs were implanted in rabbit eyes with no open capsule ring. In the treatment groups, a hydrophilic and hydrophobic version of the ring was implanted in addition to the IOLs.

Dr Kleinmann said that implantation of the hydrophilic ring was found to be easier and could be compared to standard IOL implantation. “The insertion of IOL haptics into the groove of the ring device was not automatic and required some manipulation to put it into place. Some ovalization of the capsular bag was observed, perhaps due to large diameter of the ring. The capsule remained open in the eyes with the ring implanted,” he said. Overall the study showed encouraging PCO prevention results for both hydrophilic and hydrophobic ring materials, with no significant difference found between hydrophilic and hydrophobic IOLs.

“Our results suggested primary PCO prevention due to inhibition of Soemmerring’s ring formation, indicating suppression of cell proliferation and not only a mechanical blockage. We observed about 75 per cent less PCO in the treatment eyes compared to control. In Miyake-Apple view of the capsular bag, we also saw a significant reduction of around 80 per cent in Soemmerring’s ring development in groups with the CleaRing compared to control,” he said. The cadaver study, which used a smaller ring diameter of 9.5mm, was found to fit all capsular bag sizes of eyes tested with no ovalization or deformation, noted Dr Kleinmann.

Dr Kleinmann suggests that the device’s special design of having windows in its side walls also plays an important role, as suggested by Leishman et al (Leishman L, Werner L, Bodnar Z et al. Prevention of capsular bag opacification with a modified hydrophilic acrylic disk shaped intraocular lens. J Cataract Refract Surg. 2012;38(9):1664–1670). These windows allow aqueous humor flow to the equatorial LEC, thereby maintaining nutrition and oxygen supply to those cells.

It is possible that the primary trigger for Soemmerring’s ring formation and the subsequent formation of PCO is a consequence of chronic ischemia and lack of nutrition of the equatorial LECs. This hypothesis is supported by reports describing the prevention of LEC migration by transforming growth factor β2 (TGFβ2), which is normally found in the aqueous humor (Saika S, Okada Y, Miyamoto T, Ohnishi Y, Ooshima A, McAvoy JW. Smad translocation and growth suppression in lens epithelial cells by endogenous TGF beta2 during wound repair. Exp Eye Res. 2001;72(6):679-686. Kurosaka D, Nagamoto T. Inhibitory effect of TGF-beta 2 in human aqueous humor on bovine lens epithelial cell proliferation. Invest Ophthalmol Vis Sci. 1994;35(9):3408-3412.)

 In a separate presentation, Julie Eldred PhD presented another prototype open capsular bag device, the Zephyr IOL (Anew Optics Inc.), which has shown promising results in PCO prevention in both rabbit and human cadaver studies. “We wanted to elucidate the effect of the Zephyr open bag IOL in comparison to the AcrySof (Alcon) of the lens cell progression in the open and closed bags,” she said. Dr Eldred noted that Zephyr IOL is a hydrophilic acrylic IOL designed to keep the anterior and posterior capsule separated with the haptics configured so as to allow the natural curvature of the capsular bag to be retained. The IOL also incorporates five fenestrations between the haptic and the optic to allow fluid and nutrient flow throughout the capsular bag system.

In Dr Eldred’s study, cataract operations were performed on match-paired human donor eyes in which one eye was implanted with the AcrySof IOL and the other with the Zephyr lens. The capsular bag was then removed from the globe and suspended in culture for 28 days using either serum-free media or media supplemented with two per cent human serum and TGF beta 2. Overall, the open bag IOL showed a reduced rate of cell coverage of the posterior capsule compared to the single piece IOL in both culture conditions, said Dr Eldred. This difference was more pronounced in the serum supplemented capsular bags.

“In our study, the Zephyr open bag IOL performs consistently better than the AcrySof IOL regardless of culture condition. We believe that the benefits observed with the Zephyr IOL result from a barrier function and a reduction in growth factor levels available within the capsular bag. Furthermore, the presence of serum enhanced the shrink-wrapping of the capsular bag around the IOL which we hypothesise creates an enhanced barrier to cell growth,” she concluded.