Study: OCT reliably measures anterior segment after femtosecond cataract surgery

Issue: May 10, 2013

Optical coherence tomography imaging of the anterior segment immediately following femtosecond laser-assisted cataract surgery detected morphological changes that correlated well with desired results, according to a study.

“OCT is very important during surgery because we confirm with micrometer precision where we are within the eye,” lead author Zoltan Z. Nagy, MD, PhD, DSc, an OSN Europe Edition Board Member, said. “The new high-definition OCT is of great help. By using OCT, the surgeon knows the exact anatomical relations of the eye, the depth of the anterior chamber, and can avoid further complications, such as disturbing the endothelium in patients with high hyperopia and a shallow anterior chamber. On the other hand, we are able to observe the cornea and the flat anterior capsule.”

Nagy, who was the first surgeon to perform femtosecond laser-assisted cataract surgery, was inspired to undertake the OCT study published in Journal of Refractive Surgery because he observed “very nice cuts” on the anterior capsule of the crystalline lens, within the lens and in the cornea.

“We wanted to prove that femto incisions occurred within the eye,” Nagy said. “My task is not only to perform surgery, but also to analyze the results. These incisions are measurable.”

The study

All 40 eyes in the study underwent cataract surgery performed with the LenSx femtosecond laser system (Alcon), which was programmed for a 4.5-mm capsulorrhexis, a cross-pattern fragmentation of the nucleus, a 2.8-mm main incision and a 1-mm side-port incision.

OCT imaging was conducted with the Visante (Carl Zeiss Meditec), just after femtosecond laser pretreatment. OCT for the femtosecond laser cut with the capsulorrhexis measured an average of 377 µm, compared to the laser’s programmable start of 350 µm behind the anterior lens capsule.

Nucleus fragmentation also correlated well between OCT and programmable laser measurements: 794 µm, starting in front of the posterior capsule, and 568 µm, ending behind the anterior capsule, vs. 750 µm and 550 µm, respectively, for programmed settings. Likewise, the diameter of the capsulorrhexis measured by OCT was 4.54 µm, compared to 4.5 µm for programmable settings.

The length and width of the two corneal incisions were also comparable for planned and postoperative results.

Additional results

“Overall, these results did not surprise me,” Nagy said. “However, I was surprised how nicely we could observe the cut lines within the crystalline lens created by the femtosecond laser.”

Nagy was also pleased that the formation of gas bubbles was detected within the lens and the cut planes.

“[With OCT], surgeons can judge the corneal regularity and the anterior capsule to design the depth of arcuate incisions during astigmatic correction and wound design,” Nagy said. “The surgeon is free to place the incisions anywhere in the cornea; however, peripheral incisions should be avoided because the laser can hit the conjunctiva, which could make it difficult to open the corneal wound.”

The LenSx laser system has built-in, proprietary OCT capabilities, which is important from a safety standpoint, he said.

“Femtosecond laser cuts are reproducible, and the postoperative results are more consistent and more predictable,” Nagy said. – by Bob Kronemyer

Reference:

Nagy ZZ, et al. J Refract Surg. 2013;doi:10.3928/1081597X-20130117-05.

For more information:

Zoltan Z. Nagy, MD, PhD, DSc, can be reached at Semmelweis University, Maria u. 39, H-1085 Budapest, Hungary; email: zoltan.nagy100@gmail.com.
Disclosure: Nagy is a paid consultant to Alcon.