The Five Most Important Advances in LASIK
Article by Jon Dishler, MD
There have been five major advances in LASIK since it was first invented:
1. The use of eye trackers - The first LASIK procedures required the patient to fixate on a light and that was what was used to center the treatment. The invention of eye tracker technology allows the laser to be programmed to define the location of the pupil and when the treatment is started even if the eye moves, the laser stays centered on the pupil which gives treatments that are correctly centered over the optical portion of the eye.
2. Small spot scanning lasers - The first lasers and ones still in use today use a "broad beam" where the treatment laser beam is as large as the optical zone being treated and astigmatism is corrected by varying the shape of this beam. Although this is effective, there are limitations to the types of shapes that can be created, and the quality of the ablation is limited to the quality of the laser beam. Newer lasers use small scanning spots to shape the front of the eye, and with much lower energy per laser pulse.
3. Wavefront optimized ablations - Originally LASIK was done with a mathematical model to flatten the center of the cornea to correct the refractive error. It was learned that this creates halos, glare, and other optical aberrations that are unwanted, especially in patients with larger pupils. The newer lasers can correct the refractive error but maintain a more natural or prolate shape due to more advanced algorithms for the correction.
4. All laser LASIK - All laser LASIK was initially done using a microkeratome that employs a disposable razor blade to cut the corneal flap, which is the first step in traditional LASIK. By using a femtosecond laser, Intralase, and then others were able to create a flap using a laser which is safer, more predictable, and gives more reproducible results. The razor portion is still used by many centers today, but is the cause of most of the risks of the LASIK procedure.
5. Thin flap LASIK - Initially all LASIK was done with a flap of about 180 microns. This is about 20% of the thickness of the structural cornea (the epithelial skin not counted) in most cases and the thickness was unpredictable due to use of the blade (see reason 4 above). Sometimes the flap was over 200 microns. This can weaken the cornea and lead to complications. The all laser method can make thinner flaps, and over time doctors have moved to "thin flap LASIK" with flaps of about 100 microns and in some cases 90 microns which is half as thick as the original flaps.
BONUS IMPROVEMENT: Although not technically a change in Denver LASIK itself, the diagnostic capabilities have improved since the early days of LASIK making the imaging of the cornea more robust with technologies such as OCT, Wavefront analysis, and posterior surface topography. All of these changes have contributed to making an improvement in LASIK. Recently we have begun to look at corneal hysteresis (CH) which is a measure of corneal strength.