Researchers conducting the Hungarian cataract surgery trial of the LenSx femtosecond laser have begun testing a next-generation version of the device, which employs real-time optical coherence tomography (OCT) to target laser spot locations within the anterior chamber. During the clinical trials, no laser-related complications have been reported in more than 500 eyes in which all or part of the cataract surgery was performed with the LenSx (LenSx Lasers, Aliso Viejo, Calif.).
In early patients, the anterior segment was first mapped with a separate OCT scanner to determine the laser’s target coordinates. The patient was then moved to the laser for treatment. With the combination device, a patient’s applanated eye is scanned with OCT and then, without the patient needing to move, immediately undergoes the customized, 30-second laser treatment.
“The integrated imaging capability, coupled with the precise femtosecond laser itself, reassures surgeons about the safety of using laser pulses instead of ultrasound to fragment the lens,” said Zoltan Nagy, MD, clinical professor of ophthalmology at Semmelweis University in Budapest.
Exact spot depths
“With imaging, we can be very sure about the exact depth we are treating,” Dr. Nagy said.
About half of the cataracts removed so far in the Hungarian trial have been pretreated with the laser before phaco, he said. There have been no complications, such as posterior capsule rupture. He added that real-time OCT also is expected to protect the integrity of the laser capsulorrhexis by minimizing small errors in pulse depth.
Capsulorrhexis safety
“With a 5- or 10-micron change in depth, you might not cut all the way through the anterior capsule,” Dr. Nagy said. “Then you could end up with a radial tear. With micron depth accuracy, you can be assured of a perfect capsulorrhexis, which enhances safety.”
In a presentation at the 2010 Boston ASCRS meeting, Dr. Nagy reported on 81 surgeries in which he performed anterior capsulotomy either with the OCT-equipped femtosecond laser (n=37) or manually (n=44). Retroillumination photographs taken one week and one month after surgery revealed that the capsule wrapped onto the intraocular lens optic more evenly after a laser capsulotomy than a conventional manual procedure, Dr. Nagy said.
Influences on IOL centration
IOL centration was significantly better in the laser capsulotomy-treated eyes (p=0.041), and decentration was associated with irregular capsulotomy shape, Dr. Nagy said.
“By using the computer-controlled femtosecond laser, we can perform better centration during capsulorrhexis, allowing the anterior capsule to fall evenly onto the lens optic,” he said. “Then, as the capsule contracts, there may be less vector forces that could decenter the lens.”
The results echoed those from a similar comparison that Dr. Nagy reported at the Academy’s 2009 Annual Meeting. At the time, the LenSx laser lacked integrated OCT. Laser capsulorrhexis was within ±0.25 mm of the intended diameter in 100 percent of the 60 eyes in which the femtosecond laser was used, Dr. Nagy reported. That level of precision occurred in 10 percent of manual procedures.
Tool for premium IOL implants
“Laser capsulotomy may enhance implantation of premium lenses, such as the Crystalens accommodating IOL [Bausch & Lomb],” Dr. Nagy said.
Dr. Nagy began his clinical studies of the LenSx femtosecond laser in 2008. Capsulotomy was the first procedure tested. Then came biplanar clear corneal incisions for phacoemulsification, which Dr. Nagy has reported do not require hydration. [1]
Most recently, he has pretreated cataractous lenses with the laser. This reduced average phaco power by 43 percent and effective phaco time by 51 percent, according to a small study published last December. [1]
+2 Lenses still need phaco
Dr. Nagy said his clinical experience suggests that cataracts of grade +2 and above still require ultrasound for removal.
“With up to grade 2 cataracts, the laser pulses allow removal without any phaco, while for grades +2 and above, I use the laser to pre-segment the lens into quadrants, reaching no more than 90 percent of the lens thickness,” he said.
Chopper finishes the job
Dr. Nagy said he then goes into the eye with the phaco head, grasps the nucleus with the aspiration port at 250 mm of pressure and uses an ordinary chopper to divide the nucleus along the lines cut by the laser.
“Usually little or no phaco energy is required to do this,” he said. “However, harder lenses need more. And then the quadrants can be aspirated normally.”
The LenSx device is the only femtosecond laser currently approved by the FDA for use in cataract surgery. The company hopes to have the European CE mark by the first quarter of 2011.
The LenSx Laser received FDA clearance for anterior capsulotomies in August 2009, followed by clearance for corneal incisions in December 2009, and for phacofragmentation in April 2010. Stephen G. Slade, MD, a Houston refractive surgeon and LenSx medical director, reported at ASCRS on the first 40 U.S. cataract surgeries using the laser for capsulotomy and corneal incisions.
