http://www.osnsupersite.com/view.asp?rid=19613
OSN SuperSite Top Story 12/7/2006

Rare hyperopic shift with STAAR lens likely due to capsular fibrosis, study concludes

Anterior capsular fibrosis appears to be the most likely cause of a hyperopic shift seen rarely after implantation of the STAAR Surgical one-piece Collamer IOL, a study concluded.

The STAAR Collamer lens was introduced in 2000. Since then, out of 160,000 lenses implanted, the company has received 40 reports of gradual hyperopic shift. Donald R. Sanders, MD, PhD, of the Center for Clinical Research in Elmhurst, Ill., and colleagues reviewed data for these 40 cases to determine the etiology causing the apparent degradation in refractive quality.

The hyperopic shift averaged 1.81 D, and five cases (14%) demonstrated a shift of more than 3 D. Among the 40 cases, 24 had evidence of capsular fibrosis or posterior lens displacement, and 10 cases had evidence of both.

"Anterior capsule fibrosis tends to put tension on the capsular bag, which in turn can cause the IOL to move posteriorly, producing a change in refraction," Dr. Sander and colleagues said.

In reporting the hyperopic shift, several surgeons specifically mentioned using a capsulorrhexis of less than 5.5 mm, and one surgeon told officials at STAAR that he stopped seeing cases with hyperopic shifts after switching to a larger capsulorrhexis, the study authors said.

"A small capsulorrhexis likely exacerbates the problem, leaving a greater number of anterior lens epithelial cells adherent to the anterior capsule; these epithelial cells are largely responsible for the development of anterior capsule fibrosis," the authors said.

Nd:YAG capsulotomy helped relieve the capsular tension in 14 patients. In seven of these patients, the IOL moved anteriorly, which was associated with an improvement in refraction.

"The fact that an anterior Nd:YAG capsulotomy tends to improve or reverse the refractive shifts is further evidence that [anterior capsular fibrosis] is indeed the cause," the authors said.

They noted that studies done by STAAR have also ruled out the possibility that the IOLs decreased in refractive power during their shelf life or due to improper hydration at the time of implantation.

The study is published in the December issue of the Journal of Cataract & Refractive Surgery.