PCO prevention by shockwave capsule polishing

Mar 01, 2012

Technique may provide new avenue for lens design and development

Fibrosis of the lens capsule with visual acuity lowering opacification is one of the most frequent complications after successful cataract extraction. It is, therefore, also the most frequent vision-threatening problem after cataract extraction or refractive lens exchange.

Over the years, however, cataract surgery has become both a safe and effective procedure. Intraocular lenses (IOLs) have improved and their current level is extremely precise and effective, in terms of good surgical treatment and exact IOL power calculations. In contrast to all technical advancements in phaco surgical technology and material and machine technology, prevention of posterior capsule opacification (PCO) with a posterior intact capsule has not improved.

Professor Tassignon developed a technique and a lens model preventing PCO by performing a posterior rhexis and fitting a lens into it. Such a development of course can help to maintain vision, but is not facing the cause of secondary cataract development in any way. Moreover such techniques require high levels of surgical skills and do not maintain the capsular bag and the natural barrier between anterior and posterior chamber. Our intent is to maintain the capsular bag as much as possible. First of all maintaining the posterior bag while also not modifying the natural capsular bag and its structure by applying any chemical agents whatsoever. Trials with deionized water (e.g., Milvella system) were performed in the past, but until now there has been no successful system available on the market or near to achieving market level success.

Our approach from the beginning was to preserve the natural capsular bag, but to stop cell proliferation after cataract surgery. Many years ago we started applying shock waves, generated in a small disposable laser hand piece, to the lens epithelial cells in the capsular bag. These shock waves are generated by short (3–4 ns) Nd:YAG laser (A.R.C. Laser) pulses, which are absorbed on a titanium surface.

The little plasma formation generated with pulses around 7 mJ forms small, but efficient shock waves able to blow away lens epithelial cells from the surface of the capsular bag right in front of the hand piece tips. These shock waves generated by radiation absorption in the disposable laser hand pieces can destruct the adhesion of the LECs to the lens capsule but do not rupture the capsular bag directly. Nevertheless, the energy of the Nd:YAG laser to create the plasma and the distance between capsular bag and hand piece tip are critical parameters.

We have learned that the energy value of the laser system from A.R.C. Laser has to be lower than 10 mJ, preferably around 7 mJ not to be too strong to generate plasma coming out of the hand piece. The plasma must stay inside the hand piece not to risk capsular rupture generated by plasma tissue fragmentation. Plasma that directly comes into contact with tissue is able to break up molecules and rupture the tissue, as is commonly known, from secondary cataract treatment by YAG laser capsulotomy. The hand pieces to clean up the capsular bag have an opening that allows the shock wave to exit the hand piece and hit the LECs.

Operational technique

The operational technique to remove LECs on the inside of the capsular bag requires an efficient way of directing the shock wave towards the capsular surface towards the LECs.

However, it is important not to choose a viscoelastic substance with high viscosity, such as Healon or Healon GV or comparable, as this material does not absorb the shock wave, but reflects the shock wave energy. Such a material is stiff and difficult to remove out of the eye. In case the shock wave energy is reflected at the viscoelastic substance, capsular rupture may occur. The viscoelastic has to be flexible enough with low viscosity such as Metyhlcellulose or comparable, to avoid breaking up the capsule by stressing it.

The capsule itself should be able to move whenever a shock wave impacts on its surface. The capsule cannot stand stress/tension and pressure from a shock wave at the same time. A more or less parallel direction of the shock wave towards the capsular surface helps to avoid iris trauma but also cleans the LECs from the capsular surface.

Such a technique does not require an additional viscoelastic substance to protect the iris, but irrigation to the eye bulb to maintain a deep chamber. The cleaning efficiency is less than with the perpendicular approach and more shock wave applications are required to clean the capsular surface. Our technique always followed the perpendicular approach.

Recently some surgeons decided to perform the cleaning process after lens implantation, whereas our trials were completely performed before lens implantation with an empty capsular bag. As on the one hand the method to implant the lens first and perform the cleaning process afterwards definitely adds safety to the procedure, on the other hand we do not have experience regarding efficiency of the cleaning process with the lens in place. The space for hand piece tip manipulation is smaller and the lens itself protects some of the areas in the bag from cleaning, most importantly right at the lens haptics.

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