October 2015

 

REFRACTIVE SURGERY

 

Intrastromal corneal reshaping


by Maxine Lipner EyeWorld Senior Contributing Writer

 
   

The FLIK procedure uses high intensity femtosecond laser pulses to perform intrastromal ablation.

Source: Peter S. Hersh, MD

New high-intensity femtosecond technique

Use of femtosecond technology may soon not just be limited to cutting tissue. A minimally invasive keratorefractive procedure using high-intensity, low-energy femtosecond laser pulses to perform intrastromal ablation has been developed, according to Peter S. Hersh, MD, director, Cornea and Laser Eye Institute, Teaneck, N.J., professor, Rutgers Medical School, and visiting research collaborator, Princeton University. The new technique, dubbed femtosecond laser intrastromal keratomileusis (FLIK), uses femtosecond laser pulses to perform intrastromal ablation. It is a femtosecond laser procedure based on the application of a new type of femtosecond laser, Dr. Hersh said, adding that this laser operates at an intensity level ranging from around 1,013 to 1,015 W/cm2 which is much higher than that of traditional femtosecond lasers in ophthalmology. This technique was developed in the Department of Aerospace and Mechanical Science at Princeton University by Professors Szymon Suckewer, Alexander Smits, myself, and graduate student Taehee Han. Because of this higher energy intensity of laser pulses, rather than only having the cutting effect that standard femtosecond lasers today have, it has an ablation effect as well, he said.

New style ablation

However, the ablation is done differently from either an excimer or traditional femtosecond laser, Dr. Hersh explained. It does this through a multiphoton process in which several photons are absorbed practically instantaneously by a given molecule, he said. Also, with the FLIK technique, rather than having the laser beam perpendicularly applied as with excimers and traditional femtosecond technology, it is applied from the side and a microchannel is drilled into the cornea, creating a very thin channel, Dr. Hersh explained. Then it is followed by additional pulses that create the ablation, he said, adding that the ablated materials are ejected via this entry microchannel. The goal is to remove a lenticule such as a sphere or sphero-cylinder akin to that taken out in the small incision lenticule extraction (SMILE) technique. You can think of this as combining the standard LASIK technique with the SMILE technique in that were doing intrastromal removal, Dr. Hersh said. There is no flap as there is with LASIK, but rather than mechanically extracting the lenticule, as with the SMILE approach, it is ablated intrastromally. Initially, Dr. Hersh expects the technique to be used for patients with lower degrees of myopia and astigmatism since less tissue needs to be removed, and this approach is still evolving. But ultimately it would hopefully be something that would apply to the broad range of refractive corrections, he said.

Advantageous approach

The approach should have advantages over other approaches, Dr. Hersh thinks. The advantage over LASIK is you dont have a flap, he said. The hope is by not having a flap we avoid all flap complications, and this would also keep the anterior corneal structure intact so that there is a stronger cornea afterward, Dr. Hersh said. The advantage over the SMILE technique is that rather than a mechanical technique where we have to remove the lenticule, this is just like LASIKa total laser procedure. If this can be perfected, it will give patients an intrastromal technique that works in an all-laser fashion like LASIK and would have the advantages of SMILE as well.

So far, investigators have examined cadaver and animal eyes and are encouraged. We looked at these eyes with OCT and can see the shape changes and the tissue removal changes that were doing, Dr. Hersh said. From a clinical perspective, he is hopeful the procedure will entail minimal pain. It should be quite a comfortable procedure, he said. The postoperative course should be atraumatic as well because there is no flap and there is no epithelial removal. Currently, some refinements are still being made. We have to work on further decreasing our channel width in order to minimize any surface disruption, Dr. Hersh said. In a perfect world, one would have an intrastromal ablation where there was absolutely no conduit to the surface, he said; however, LASIK has a big conduit and SMILE a conduit as well. We want to make this as intrastromal as possible, with the least distortion to the ocular surface, he said. Investigators are also working on refining the degree of tissue removal using the multiphoton approach, Dr. Hersh said, because one can remove a lot of tissue with a single laser pulse with this technology, and we want to minimize that and make the tool that were working with even more accurate than current excimer technologies. He expects this to take about 1 year or so.

Dr. Hersh is very hopeful about where this is headed. The ultimate goal, as with any refractive procedure, is to have a very safe procedure, with minimal pain and minimal recovery and the greatest accuracy, he said. With a procedure like this, we hope to combine the benefits of the accuracy and the excellent results that were having to date with LASIK with the safety, the comfort, and the rapidity of healing that we would have with an intrastromal procedure.

Editors note: Dr. Hersh has financial interests in the procedure.

Contact information

Hersh: phersh@vision-institute.com

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