Femtosecond laser is an exciting new technology originally FDA approved for use in refractive surgery. The FDA has now expanded the indications to include ‘cuts’ in the cornea, including vertical and lamellar cuts. The possibilities for use now include but are not limited to femtosecond keratoplasty, astigmatic keratoplasty, and Intacs for keratoconus.
Femtosecond laser differs from the traditional method of refractive surgery in a number of ways. This technology uses a near infrared light to create precise subsurface cuts. Traditionally in refractive surgery, ultraviolet light sources, such as the excimer laser, have been used for precise surface cuts on the cornea. These light sources were dependent on the tissue properties to absorb the light. Femtosecond laser, on the other hand, works independently of light tissue absorption so photodisruption of deeper tissues is possible and the patient’s anatomy, such as steepness, flatness or thickness of the cornea, will not interfere with the cuts. This leads to a more uniform treatment. In addition, femtosecond pulses are very short, subpicosecond duration, which allows lower energy levels and aids in precision. The lower energy also decreases collateral damage.
Traditional methods for cutting the LASIK flaps include the use of a microkeratome blade, an oscillating blade which creates a shear factor, according to Dr. Sonia Yoo at the Bascom Palmer Eye Institute in Miami, Florida. In a patient with a weak epithelium, there is increased risk of a resulting epithelial defect. With the femtosecond laser creating the flap, there is no shear factor and the risk of an epithelial defect is less.
To reiterate, femtosecond laser allows extreme precision in surgery. In one study presented this year at the American Academy of Ophthalmology, femtosecond laser incisions achieved perfect diameter accuracy in 100% of cases, while only 10% of surgeons' manual cuts were within 0.25 mm error.
With the FDA label extension, femtosecond laser technology is spreading, with its largest impact on the future of cataract surgery. This technology was a highlight at this year’s American Academy of Ophthalmology in San Francisco.
In an interview given by Dr. Carmen Puliafito, Dean of USC Keck School of Medicine, to Ophthalmology Web, femtosecond laser technology was discussed. “The preliminary results are very promising,” states Puliafito. “I think that we are going to see the use of laser based technology in cataract surgery emerging over the next few years.” Dr. Puliafito mentioned that there are 3 manufacturers now that have introduced femtosecond high repetition rate laser systems which allow a very reliable capsulotomy and essentially liquefy the lens and enhance phacoemulsification.
Existing femtosecond laser systems such as IntraLase, which are used in corneal transplants and to make LASIK flaps, don't penetrate far enough for capsulotomies, William Culbertson from Bascom Palmer Eye Institute noted at the meeting.
But a new generation is emerging that reaches deeper into the eye (7,500 versus 1,200 ìm). One such system (LenSx) gained FDA approval recently for use in cataract surgery, and two others are under development (Optimedica and LensAR).
Dr. Sonia Yoo states that femtosecond cataract surgery is the next up and coming application with this technology. Advantages are the wound, capsulorhexis and lens chopping can be done reproducibly and can facilitate lens removal. Disadvantages are the cost, however, if the technology reduces complications, then the benefits may outweigh the costs. “Or maybe the patients will end up paying out of pocket for the technology, similar to how they pay out of pocket for premium IOLs," states Yoo.
Dr. David Goldman, corneal surgeon at Bascom Palmer Eye Institute, also spoke with Ophthalmology Web at AAO this year. He also discussed how femtosecond lasers in cataract surgery create a very controlled capsulorhexus and can break up the lens into many pieces which means they can be removed through a small incision. “The real benefit of this is going to come in several years when we can develop an injectable IOL in gel form,” says Goldman.
Dr. Jean-Marie Parel at Bascom Palmer Eye Institute is working on just this very thing: an injectable gel intraocular lens. The lens refilling project is called Phaco-Ersatz and has been a work in progress since prior to 1986 when the first paper was published with Dr. Edward Norton. Dr. Parel states that the project is going at light speed now that there is substantial funding. A human trial is planned for the end of 2010.
Follow up questioning of Dr. Goldman after AAO reiterated the benefits of gel IOLs but also led to one concern: “What happens if you have to YAG the posterior capsule – how do you keep the gel from going back into the vitreous?”
Dr. Parel states that the Phaco-Ersatz project and human trials will include a thorough anti-posterior capsule opacification program because of concerns that, as for any accommodating IOL, once you break the posterior capsule, you risk extrusion into the vitreous cavity. As well, with the gel, a bowing through the capsulorhexis may cause major ametropia.
Phaco-Ersatz is a very exciting and highly anticipated project. Injectable gel IOLs have the main advantage of restoring accommodation, according to Dr. Yoo. So far, this technology is not available commercially.
Ophthalmologists around the world look forward to the increasing applications of femtosecond laser. Its use has already gained widespread popularity as evidenced by the focus at AAO this year and we look forward to its impact on cataract surgery coupled with injectable intraocular implants.