Study: Femtosecond laser anterior capsulotomy more accurate than manual method

The technique enables surgeons to override the built-in navigation system to center the capsulotomy and optimize effective lens position.

Keith Edwards

Laser anterior capsulotomy offered more precise capsule opening than manual continuous curvilinear capsulorrhexis, a study found.

The LensAR laser system was used to perform all laser anterior capsulotomies.

“What we found was what we expected, which is that the capsulotomy created with the laser is much closer to the intended diameter than the manual method,” Keith Edwards, FCOptom, vice president for clinical and regulatory affairs of LensAR, said in an interview with Ocular Surgery News.

The LensAR laser received 510(k) clearance from the U.S. Food and Drug Administration for anterior capsulotomy in May 2010.

“Obviously, these data were part of our submission to get our 510(k) approval for the system,” Dr. Edwards said. “With the combination of the ease of removal and the precision of the capsulotomy, we felt that this was a very good, reliable system that would be of benefit to surgeons.”

The study was published in the Journal of Cataract and Refractive Surgery.

Programming and control

The LensAR system has a proprietary infrared-based imaging system that uses scanning super luminescent diode technology to generate an image of the eye and direct short laser pulses to targeted areas, Dr. Edwards said.

“The imaging system uses the same optical pathway as the laser, so it’s basically confocal and coaxial, so you don’t get any systematic errors between where you measured and where you place the laser shots,” he said.

The desired size and position of the capsulotomy, based on images of the anterior segment, can be programmed into the laser software. However, the surgeon can override the programming and center the capsulotomy to optimize IOL positioning, Dr. Edwards said.

“The surgeon has control over the diameter he wants, and that’s going to be a function of the IOL that he’s going to implant,” he said. “Some may require different diameters. The belief is that if you get a well-centered, regular capsulotomy of the right size every time you do it, then your effective lens position will be more consistent from patient to patient.”

In addition, the laser procedure can be learned quickly, he said.

“We’re finding that there really isn’t any learning curve. The first patient usually gets a good result, and it only gets better from there. So, the learning curve is pretty minor,” Dr. Edwards said.

Study methods, results

The study included 53 eyes that underwent laser anterior capsulotomy and 28 eyes that underwent manual continuous curvilinear capsulorrhexis. Investigators retrieved and analyzed capsule buttons from each group.

Buttons were stored in a balanced salt solution before measurement. They were lightly stained, laid flat on a microscope stage and photographed with a digital camera. Proprietary image analysis software was used to compare the achieved and target diameters of the buttons; targeted diameter was typically 5 mm.

“We actually take the capsule button out and measure the button. That allows us to use a photographic method,” Dr. Edwards said.

Ease of button removal was rated on a scale of 1 (largely uncut capsulotomy requiring manual capsulorrhexis) to 10 (free-floating button that required no manual detachment from the remaining capsule).

Study results showed that mean deviation from intended diameter was 0.16 mm in the laser capsulotomy group and 0.42 mm in the manual continuous curvilinear capsulorrhexis group; the between-group difference was statistically significant (P = .03).

Mean absolute deviation from intended diameter was 0.20 mm in the laser capsulotomy group and 0.49 mm in the manual continuous curvilinear capsulorrhexis group. The difference attained statistical significance (P = .003).

“[In] this case, actual deviation and absolute deviation from intended diameter were both significant, so it doesn’t matter how you analyze it — it’s a much better result,” Dr. Edwards said.

The median rating for ease of removal was 9 (range: 5 to 10); almost half of cases were rated with a score of 10.

Four buttons in each group were rejected as incomplete and impossible to analyze.

Further study on histological and biomechanical factors associated with stability of the capsule opening is warranted, the study authors said. – by Matt Hasson

Reference:

• Tackman RN, Kuri JV, Nichamin LD, Edwards K. Anterior capsulotomy with an ultrashort-pulse laser. J Cataract Refract Surg. 2011;37(5): 819-824.

• Keith Edwards, FCOptom, can be reached at LensAR Inc., 2800 Discovery Drive, Orlando, FL 32826; 407-965-1360; fax: 407-386-7228; email: keith.edwards@lensar.com.
• Disclosure: Dr. Edwards is vice president for clinical and regulatory affairs of LensAR.