March 2010

 

CATARACT /IOL

 

PCO elimination by anterior capsule polishing with a shock wave


by Wolfram Wehner, M.D., Maximilians Eye Clinic, Nuremberg, Germany

 

 

In our laboratory at the John A. Moran Eye Center, University of Utah, Salt Lake City, we have the opportunity to evaluate different methods for prevention of posterior capsule opacification, including surgical and intraocular lens related factors. We have recently evaluated a modified laser photolysis system that removes lens epithelial cells via shock waves after capsular bag evacuation. Studies done in cadaver eyes, including immunohistochemical analyses performed in collaboration with the Emory Eye Center, Atlanta, revealed that not only lens epithelial cells but also proteins such as fibronectin and laminin were absent in the laser treated areas. These results were presented at the 2009 ASCRS Symposium and Congress (Mamalis N, Grossniklaus HE, Waring GO III, Werner L. Histopathologic analysis of ablation of lens epithelial cells with a laser photolysis system. Best Paper of Session Award, Session 4H, April 7, 2009, San Francisco). Dr. Wolfram Wehner from Germany has been using this system since early 2006. I requested that he summarize his clinical experiences so far, which you will see show promising results in terms of PCO prevention.

 

Figure 1: Laser handpiece for capsule polishing

Figure 2: PCO development for a time period of more than two years

Figure 3: PCO development on only one side of the capsular bag

Today cataract surgery has become a technically advanced and very standardized procedure. The outcome for the patient is very predictable and in the majority of cases after 1-2 days the patient completely recovers from the surgery and the visual acuity reaches best values. Posterior capsule opacification is the most common problem post-op, which results in a decrease of the visual acuity, preferably treated by Nd:YAG laser posterior capsulotomy. Although this is a routine procedure, the natural accommodation is lost after cataract surgery and all efforts need to be made to leave an intact capsular bag for possible implantation of an accommodative lens. Moreover, it would be very beneficial for every patient if the posterior capsular bag was not opened by capsulotomy, as this procedure destructs the natural barrier between anterior and posterior segments. The majority of attempts with lens designs and materials for accommodative lenses rely on intact capsular bags; as a result of this, we have to avoid opening the capsular bag.

More than three years ago we started to use the shock wave of a Nd:YAG laser from ARC Laser (Nuremberg, Germany) not only for lens emulsification (Dodick Photolysis) but also for lens epithelial cell removal. To use the shock wave generated with special handpieces not for destruction of lens material but to remove cells from the capsular bag, the energy output of the laser and the design of the handpieces had to be modified. We decreased the energy level that normally was used for cataract removal (about 11 mJ) to 8 mJ, and we bent the handpiece tips for easier application of the shock wave at the inner side of the capsular bag. While performing the lens exchange, access to the inner capsular bag, where lens epithelial cells start to proliferate later, is obtained anyhow. Any other attempt would require another surgery. Besides other techniques of killing the lens epithelial cells (e.g., Milvella system using irrigation with distilled water), removing the lens epithelial cells may prevent PCO.

To investigate clinically the preventive effect of the ARC Nd:YAG Laser Dodick Photolysis shock wave removal of lens epithelial cells after phacoemulsification of cataract on PCO occurrence, in a first series 17 eyes of 17 patients were treated with the ARC Laser PCO prevention system. The laser unit, developed for the treatment of the inner compartment of the capsular bag, is based on a modification of the Dodick Laser Photolysis system. We reduced the energy of the laser system to 8 mJ to achieve a cleaning effect but not to be in danger of capsular rupture. The laser light, which is delivered into the handpiece (Figure 1) via a fiber optic with a diameter of 283 microns is absorbed on a titanium plate. High absorption leads to plasma formation and immediate shock wave expansion. This shock wave, not the laser irradiation, is used to remove the lens epithelial cells from the inner side of the anterior capsular bag. The patients were consecutively treated within two months in February and March 2006. The age was 69 ± 8.4 years , the youngest patient was 54 years old, the oldest 82 years old. All eyes were treated after successful standard coaxial ultrasound phacoemulsification. Exclusion criteria were the following: pseudoexfoliation of the lens capsule, keratoplasty or other corneal surgery (including refractive corneal surgery), poor pupil dilatation, retinal diseases including diabetic retinopathy, weak zonules, and previous vitreo-retinal surgery.

All cataract extractions were performed via a temporal limbal incision of 2.6 mm width. A paracentesis 90 degrees away was made for the manipulator. Methylcellulose as viscoelastic was only used right before phacoemulsification and before implantation of the lens, after the cell cleaning process. In the beginning of the surgery a 5 mm continuous circular capsulorhexis was created by cystotome. Hydrodissection and hydrodelineation of cortex and nucleus were performed in each case according to our standard procedure. After complete unimanual phacoemulsification of the lens nucleus and epinucleus and irrigation/aspiration of the lens cortex, the lens cell removal process was started. The ARC Laser handpiece was introduced into the 2.6 mm incision and its tip was directed within the capsular bag, without touching it. Pulses were then applied to the inner surface of the anterior capsule only under direct visualization. Each laser pulse created a shock wave that detached the lens epithelial cells from the capsular bag, a process that could be observed directly under the operating microscope. In the first series, the lens cell removal was done only on the nasal side of the anterior capsular bag from 6 o’clock to 12 o’clock. The posterior capsular bag side was not cleaned. About a 180-degree circumference was treated with 45 pulses (± 12 pulses) per eye in the cleaning process. For performing the lens cell removal, the handpiece was connected to the irrigation. The bottle height was set at 30 cm. The laser was set at 8 mJ output energy, which results in a shock wave strong enough to effectively remove the cells. The pulse repetition rate was set to 1 Hz to control each shock wave delivery. After we observed iris trauma in the beginning of the capsule polishing, we developed a method to remove the cells without causing any iris trauma. We used HPMC, which is placed between the iris and capsular bag before the treatment begins. For application of the shock wave, the handpiece is inserted into the capsular bag through the phaco paracentesis and afterward through a second smaller paracentesis opposite to the other. Three hundred sixty degrees of the anterior capsular bag are treated with the shock wave. Additionally, we have now set the energy to 7 mJ, which after the first results is sufficient for cleaning. A further series of 30 patients was treated with a 360-degree cleaning.

Regarding the results, we used a scale for the graph differentiating between mild, moderate, and severe PCO. The classification was done optically by slitlamp examination. Figure 2 shows the PCO growth over time for a follow up of more than two years. All the data displayed show the mean values of the 17 eyes.

The temporal not cleaned side of the anterior bag showed usual fast cell growth within two weeks. The cleaned nasal side of the anterior bag stayed clear except for one eye with mild PCO. The temporal not cleaned posterior capsule developed severe PCO over time as expected. Unexpectedly, the nasal not cleaned side of the posterior capsule differed from the temporal side showing none to mild PCO, equal to the situation on the cleaned anterior capsule. It has to be mentioned that there was no cleaning on the posterior part of the capsule (Figure 3). Our first attempts to prevent PCO intraoperatively during cataract surgery seem to be quite successful. We have followed patients for more than two years and have seen significant differences between treated and untreated areas in the capsular bag regarding PCO. The untreated 180 degrees of the capsule got much more cell proliferation in comparison with the treated opposite side. Interestingly, the posterior capsule also showed more cell proliferation temporally than nasally, although we cleaned only the anterior capsule and no shock wave pulses were applied to the posterior capsule. We hypothesize that the shock wave exposure also affects the equatorial cells and prevents cell migration efficiently. To investigate this in more detail, immunohistochemical studies using cadaver eyes are being performed at the Moran Eye Center, in collaboration with the Emory Eye Center. As a next step we cleaned not only 180 degrees of the anterior lens capsule, but 360 degrees. We have treated more than 30 patients without any complications. We will follow up the patients for three years minimum, and several other centers also started to use this method to clean the inner capsular bag on the anterior side to prevent PCO. To date, no method to prevent PCO has provided acceptable efficiency or could be applied easily in a way that most cataract surgeons would accept for routine application. Our method does not require additional surgery and can be done after the routine lens exchange process easily. It takes less than three minutes to perform and no chemicals or artificial elements are needed. It is simple, and hopefully we will get the chance to pave the way for a new decade in cataract surgery where lenses can be implanted preserving accommodation in a natural capsular bag not opened by YAG capsulotomy.

PCO elimination by anterior capsule polishing with a shock wave PCO elimination by anterior capsule polishing with a shock wave
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