The femtosecond cataract laser introduces a level of safety, efficacy and reproducibility that will benefit all cataract surgeons
The most talked about development in cataract surgery in at least 10 years is the development of femtosecond lasers for cataract surgery. As someone who had the good fortune of working with one of these systems since its early inception, I think there is very good reason for this excitement, particularly when you consider that for the first time since phacoemulsification became the technology of choice we now have a significant evolution in cataract surgery.
For those of us who have been performing cataract surgery since the 80s and 90s; we are well aware of previous attempts to create lasers that would replace phaco. However, none ever reached commercialization because they were simply not as efficient, safe and effective as phaco. With the femtosecond laser for cataract surgery we have a different story. I've been working with the LenSx femtosecond laser (LenSx Lasers Inc., Aliso Viejo, California, USA) since 2008 and have witnessed its remarkable evolution. Here, I will explain the differences between current cataract surgery technology and the femtosecond laser, as well as provide some clinical results from our now two year experience.
Limitations of current technology
From a technology standpoint, complications due to excess ultrasound energy may result in corneal wound burn, corneal edema and endothelial cell loss. From a technique standpoint, the creation of the capsulorhexis using a manual technique remains the most difficult yet important step in the surgical procedure, particularly when implanting a premium IOL. One review of more than 2,600 cataract surgeries found an anterior tear rate of 0.8%, with 40% of these tears extending into the posterior capsule and 20% being so significant that vitrectomy was required.1 The incidence rate of capsular tears increases in residents as they are learning the technique, with one study reporting a rate of 5.3% for anterior tears.2
When you compare the outcomes currently achieved with cataract surgery, with the visual outcomes achieved with LASIK, the predictability of the distance correction is about half of that seen with LASIK, while the complication rate is 10 times higher than LASIK.
Understanding the anterior segment
With the advent of femtosecond lasers for refractive and corneal surgery, we began to understand that it was possible to go through the corneal surface and quite effectively create incisions within the tissue. The success of this approach raised the question of whether a femtosecond laser could be developed to work more posteriorly in the eye, primarily within the anterior segment.
The first step of the procedure that we attempted was creation of the anterior capsulotomy. This was followed by the technique to liquefy or fragment the lens and then, finally, to create the corneal incisions.
Today, the LenSx system uses a proprietary optical coherence tomography (OCT) system that provides real-time images of the anterior segment. To use the system, the surgeon first programs the corneal incisions, the capsulotomy and the lens fragmentation pattern. The eye is docked to the laser and the integrated OCT rapidly captures three-dimensional images of all ocular structures within the anterior segment. These images are projected onto the video microscope screen along with overlays of the pre-programmed laser treatment. The surgeon then makes any adjustments via touch screen and then begins the treatment. Fragmentation of the lens is accomplished first, followed by the creation of the anterior capsulotomy and then the corneal incisions.
The perfect capsulorhexis
The importance of creating a well-centered and intact capsulorhexis has become even more critical with the growing usage of premium IOLs. With both accommodative and multifocal IOLs, the performance of the lens can be hampered by an imperfect or decentered capsulorhexis. For example, with a diffractive multifocal, such as the ReSTOR (Alcon Labs, Ft. Worth, Texas, USA), if the capsulorhexis is too small, it can result in glare, halos and night driving problems.
With a femtosecond laser we are now able to create a perfect capsulorhexis - one that is well-centred and sized according to patient and IOL requirements. In a study that we conducted with the LenSx system, we compared 37 anterior capsulotomies created with the laser to 44 manually created capsulorhexis. Centration of the IOL was then measured at 1 week and 1 month postoperative using retroillumination photos and a photo software program. The attempted capsulorhexis size was 4.5 mm in both groups.
The results showed that there was significantly better centration of the IOL in the laser group compared to the manual capsulorhexis group (p=0.041). Anterior capsule overlap with the IOL edge was also better in the LenSx group, which perhaps may help prevent PCO. This study also showed that IOL decentration was associated with irregularity of the capsulorhexis shape.