Understanding how the laser cataract environment differs from the traditional
An example of posterior capsule rupture
Source: David Allen, F.R.C.Ophth.
It happened without warning—two cases of the very rare capsular block syndrome occurring among the first 50 femtosecond laser-assisted cataract surgeries performed at an Australian center, according to Tim V. Roberts, M.D., consultant ophthalmic surgeon,
Vision Eye Institute and Royal North Shore Hospital, Sydney.
"We were doing phaco the same way that we [typically] had," Dr. Roberts said. The practitioners, who had only just begun to adapt to the femtosecond-assisted procedure, immediately stopped to take a closer at what was occurring. After uneventful combined laser fragmentation, capsulotomy, and corneal incision procedures, things had suddenly gone awry in both cases, resulting in posterior capsule rupture with dislocation of the lens.
Surgical paradigm shift
Fortunately the procedures had been videotaped. "We had an expert panel look at these, and the universal consensus was that there was no problem with the laser at all," Dr. Roberts said. "During vitrectomy you could actually see the crucial cuts, and you could see the gas in the nucleus, so it was 100% certain that the laser had not lasered the posterior capsule."
The femtosecond laser had done exactly what it was supposed to do. The problem was that with the use of the laser to assist in cataract removal there had been a paradigm shift. "When you do femtosecond laser cataract surgery, it is not the same as doing routine manual phaco," Dr. Roberts said. "What these cases have indicated to laser cataract surgeons is that the intraocular environment changes when you do femtosecond laser surgeries."
With these surgeries the introduction of intracapsular gas from the femtosecond laser changes the intraocular environment. As a result, there is increased volume in the capsular bag. "You've got a perfect capsulotomy that potentially can give you a capsulotomy block if the hydrodissection fluid doesn't flow around the cataract and out through the laser cut capsulotomy when you do these perfect 5-mm cuts on the surface," Dr. Roberts said.
Altering the approach
After examining the videos, investigators altered some steps in the procedure to ensure safety. Dr. Roberts finds that there are four key changes to make. The first thing is to ensure that you do not overinflate the anterior chamber with OVD. Secondly, it's important to offer the fluid an avenue of escape. "Ensure that if you are hydrodissecting that you decompress the posterior lip of the wound with the elbow of the cannula," Dr. Roberts said. "That helps viscoelastic and fluid to come out of the anterior chamber." Thirdly, practitioners must be cognizant of offering the gas a way to escape. "Because these wounds are beautifully water tight, you gently lift the edge of the capsulotomy with the cannula and try and release gas," he said. "The other recommendation is that if there's a lot of gas, go in before you do a hydrodissection, break the cataract into two hemispheres via the laser lysis fragmentation pattern, release all of the gas, and then do the hydrodissection after that."
In essence, you are ensuring that excess pressure does not build up in this new femtosecond environment. "If you have gas there that can't compress and then you put in the hydrodissection fluid and if the capsulotomy around it seals, then the fluid and the gas create such a volume that potentially it can cause a posterior capsule rupture," Dr. Roberts said. "Once you release all of the gas from the capsular bag then you are unlikely to increase the volume."
These steps help to ensure the safety of the procedure. "Right now we're in a position where we haven't had a complication in over 600 cases, and we're getting extremely good results," Dr. Roberts said. Both of the initial two patients ultimately fared well; both attained 20/20
He sees these two early cases of capsular block as growing pains, mirroring the first days of phacoemulsification. "It's akin to when phaco was first introduced—the incidence of posterior capsular rupture and dropped nuclei increased dramatically," Dr. Roberts said. "Then within months as surgeons learned how the technology behaved and how to adapt to the technique, the complication rate flattened off."
Dr. Roberts stressed that this is not a technology-derived complication in the sense that the laser is doing exactly what it was meant to do. The takeaway point is that you have to understand the change in surgical technique and intraocular environment during laser cataract surgery.
In his personal opinion, Dr. Roberts believes the femtosecond laser has the potential to improve the accuracy and predictability of cataract surgery. "If you look at the LASIK peer-reviewed literature against cataract [procedures], LASIK has a 97% predictability while cataract surgery is still at 50-60%, so as cataract surgeons we need to be constantly looking for ways to improve our surgery and refractive results."
Since those two early cases there have been no further complications, and investigators have been getting good results with the laser-assisted technique, all of which Dr. Roberts thinks bodes well. "I certainly believe that it is the technology for the future and will be the next paradigm shift in terms of how we do cataract surgery," he said.
Editors' note: Dr. Roberts has financial interests with Alcon (LenSx, Fort Worth, Texas).