New IOL Technique Reduces Posterior Capsule Opacification
Modern-day cataract surgeons have long struggled to address their most common complication—posterior capsule opacification (PCO). PCO can occur during the healing process that the capsular bag goes through after crystalline lens removal and IOL placement. As the capsular bag heals, the lens epithelial cells remain behind the bag. Here, they may proliferate and possibly transform as they come into contact with cytokines, a group of proteins and peptides (ie, signaling compounds) that are released after surgical trauma. PCO has also been linked to IOL biomaterial after lens-in-the-bag surgery.1
Improved surgical techniques have reduced PCO rates by 11% and 13% at 4 and 5 years postoperatively, respectively. Primary posterior continuous curvilinear capsulorrhexis, introduced to block proliferation of the lens epithelial cells at the visual axis, is one such improved technique. We found, however, that this procedure alone has little effect on reducing PCO rates.
Most recently, surgeons have turned to Nd:YAG laser capsulotomy to treat PCO. This technique presents several known complications including the unavoidable rupture and permanent disruption of the anterior hyaloid membrane. As the capsular bag heals, PCO complications can range from Elschnig pearls or posterior capsular fibrosis to wrinkling of the anterior and posterior capsule.1
BAG-IN-THE-LENS CONCEPT
Introduced in the late 1990s and first implanted in humans in 2004, the bag-in-the-lens hydrophilic acrylic IOL consists of a 5-mm optic surrounded by a peripheral groove that is defined by elliptical haptics.2 These haptics are perpendicularly oriented to each other, allowing for accommodation of both the anterior and posterior capsulorrhexis. Because the IOL accommodates both capsules, it has been called the bag-in-the-lens implant, compared with the commonly used lens-in-the-bag technique where the capsular bag accommodates the IOL (Figures 1A and B).
Bag-in-the-lens implantation requires a slightly different surgical technique than its lens-in-the-bag counterpart. First, the surgeon must create a perfectly sized anterior capsulorrhexis, slightly smaller than the 5-mm optic. An equally sized capsulorrhexis should also be created posteriorly.3 If performed properly, we found that this technique reduces the chance of vitreous prolapse, and the lens reduces PCO rates.
We examined 200 patients; 100 patients (group one) underwent bag-in-the-lens implantation with the 89A Morcher IOL (Morcher GmbH, Stuttgart, Germany), and 100 patients (group two) underwent the lens-in-the-bag implantation technique (92S Morcher IOL; Morcher GmbH). Both IOLs are made of identical biomaterials. All study parameters (ie, IOL power, surgeon, age, follow-up) were matched for both groups.
Mean age for group one was 68.56 years (range, 39–88 years), with a mean follow-up of 17.03 months (range, 2–57 months). The mean IOL power was 20.88 D (range, 15.50–25.00 D). Mean age for group two was 69.4 years (range, 18–90 years) with a mean follow-up of 16.68 months (range, 2–56 months). The mean IOL power was 21.05 D (range, 13.00–25.00 D). Our aim was to determine the Nd:YAG laser retreatment rates in both groups.
Using the Kaplan-Meier survival analysis, we found that no Nd:YAG treatments were needed for group one (ie, bag-in-the-lens patients). Nd:YAG treatment was increasingly needed during follow-up for patients in group two (ie, lens-in-the-bag patients).
No signs of visual axis reproliferation were found among the 817 bag-in-the-lens implantations we performed between 1999 and 2006, including 36 eyes of adolescents and infants, with follow-up for all eyes ranging from 6 months to 6 years. On slit-lamp examination, we also discovered no reproliferation on the anterior hyaloid.4 In addition to the long-lasting transparency of the visual axis, the bag-in-the-lens IOL is also positioned along the line of sight by the surgeon. A ring caliper (Morcher GmbH) was also developed to size and center the lens along the first and third Purkinje reflexes.5
In a second study of 50 eyes implanted with the bag-in-the-lens IOL (with Purkinje reflexes used for centration), we found that a majority of the lenses were decentered slightly nasally. We also found that the lenses had high stability with rotations of less then 1.5º. These results allowed for the incorporation of toric correction in the lens optic as well as compensation for spherical aberrations at the optic's posterior surface.
Lastly, we examined the uveal response in vitro by preparing postmortem human lens capsules and placing them in a culture for 4 weeks. We split these capsules into three groups: virgin capsular bags, capsular bags equipped with bag-in-the-lens IOLs, and capsular bags equipped with lens-in-the-bag IOLs. After tissue growth factor was added to the culture to stimulate epithelial cell growth, we found striking results; only capsules equipped with the bag-in-the-lens IOLs retained transparency. This information confirms our previous conclusion that the visual axis of eyes with a bag-in-the-lens implantation will constantly remain clear (Figures 2A through D).
TORIC AND ASPHERIC IOLs
I hope that we will see toric and aspheric bag-in-the-lens IOLs become available in the near future. Before this can happen, however, we need to solve a few problems.
First, there are no current benchmarks (based on large-scale epidemiological studies) to determine the appropriate degree of asphericity. Second, we need to address restoration of accommodation.
The current bag-in-the-lens IOL does not interfere with the peripheral capsular bag, and it can be used in conjunction with a capsular bag accommodation ring that aims to restore the capsular equator angle. We have found that children had a mean accommodation of 3.50 D, and adults (with an axial length of 22 mm or less) had an average accommodation of 2.75 D, allowing for spectacle-free reading.
We need to find a similar solution for the toric and aspheric versions of this lens.
CONCLUSION
Although skeptics may point out the difficulty of creating a specifically sized capsulorrhexis for the bag-in-the-lens method, I believe the introduction of the ring caliper eliminates potential complications.
We could, however, use improvements in tracking devices to improve centration of the anterior and posterior capsulorrhexis along the visual axis. These improvements would be more accurate than depending on the Purkinje reflexes. With these improvements and a proven method to address accommodation, I believe that the bag-in-the-lens technique may find a place in every surgeon's armamentarium and continue to reduce PCO rates.
Marie-José Tassignon, MD, PhD, FEBO, is Head of the Department of Ophthalmology at the University Hospital Antwerp, in Belgium. Dr. Tassignon states that she owns a patent for the bag-in-the-lens IOL concept (Morcher GmbH, Stuttgart, Germany). She may be reached at Marie-Jose.Tassignon@uza.be.
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