How Does Laser Vision Correction Surgery Work?

 

There are different methods to correct one's vision.  While the eponyms run wild (LASIK, LASEK, EpiLASIK,  iLASIK, IntraLASIK, No-Blade LASIK, PRK, SA, ASA), each of these modalities improves your vision by subtly changing how the outer window of the eye (the cornea) bends light.  The difference in the technologies depends upon the specific technique the surgeon utilizes to effect the change in the eye's strength, and to some degree it is dictated by the nuances of each patient's characteristics.  Indeed ALL forms of vision correction be it glasses, contacts, or surgery involve altering the eye's focusing ability. 

 

Currently, in the US all laser correction technologies involve gently contouring the cornea through the use of an EXCIMER LASER (my excimer laser of choice is the Wavelight Allegretto 400 EyeQ system).  All excimer lasers - including the Wavelight laser, the VISX S-4, LADARVISION or Nidek, utilize Argon and Fluoride gas to create and Excited diMER which emits the energy required to generate the laser beam.  The wavelength of the excimer laser beam used in refractive surgery is 193 nanometers.  This wavelength is important because it is just strong enough to disrupt the carbon - carbon and carbon nitrogen bonds on the surface, but not strong enough to go beyond the surface of the cornea.  This relatively low laser energy is important because only the tissue directly in contact with the beam is altered - nothing goes inside or through the eye.  The laser is so weak that if you placed your hand under the laser while it is firing you would not feel it (yes, after 8,000 or so cases I can now admit that I did this as a fellow - hey, I was young and impressionable, but what the heck...). 

The excimer laser was originally designed to pattern computer chips, when an ophthalmologist named Steven Trokel proposed using this instrument to make the ultimate radial keratectomy (more on this in another blog) incision.  After initial tests, it was found that the excimer laser could perform more accurate corrections through surface contouring as opposed to using it for incisions.