How the Excimer Laser Works

The excimer laser generates ultraviolet light of a very specific wavelength (193 nanometers) when electricity enters a chamber containing argon fluoride gas. The term excimer comes from two words: "excited" and "dimmer"; these terms are used to describe the reaction in which the laser transfers energy through the ultraviolet beam of light. The pulses of light with controlled and specific wavelength are the basis for the excimer laser's use in shaping the surface of the eye.
     

How Precise is the Laser?

The ultraviolet light emitted by the excimer laser will reshape only about 0.25 microns of corneal tissue per pulse. To understand how precise this is, 200 pulses would be required to etch through a typical human hair, which is about 50 microns in diameter! You could place your hand beneath the laser during a pulse and wouldn't feel a thing. This precision is the basis for Laser Vision Correction.

What Does the Laser do to the Eye?

When the laser beam touches the cornea (the surface of your eye), the intermolecular bonds are changed and the molecules rapidly disperse into the air. This leaves a clear and smooth, underlying, corneal surface.

From Summit Technology, Inc.:

Photorefractive Keratectomy Approval Requirements:: Approval is for Summit Technology's application for the SVS Apex laser to correct mild to moderate nearsightedness (-1.5 to -7.0 diopters when concomitant astigmatism is no greater than 1.5 diopters) in a procedure called photorefractive keratectomy (PRK) using an excimer laser that emits light at a wavelength of 193nm. PRK is an elective procedure with the alternatives being eyeglasses, contact lenses or radial keratotomy. Approval of the application is based on clinical trials of more than 1600 eyes together with safety information through 3 years of follow up. The studies using the 6mm treatment zone found that of the 341 eyes at 6 months, 95% were corrected to 20/40 or better without spectacles or contact lenses, and 66% to 20/20 or better without spectacles or contact lenses. In 23 out of 340 eyes (6.8%), the best vision that can be achieved with spectacles declined by 2 or more lines from preop; none was worse than 20/40. These clinical trials showed the following transient complications: pain (24-48 hrs.), corneal swelling, double vision, feeling something in the eye, shadow images, light sensitivity, tearing and pupil enlargement. These problems lasted up to several weeks.The clinical trials using the 6mm treatment zone showed the following adverse events occurred in at least 1.0% of the patients within 6 months post-treatment: night vision difficulty (1.0%); elevation of intraocular pressure (1.8%); hazy cornea affecting vision (2.3%); overcorrection or became farsighted (5.0%); undercorrection or still nearsighted (5.6%); loss of the best vision that can be achieved with glasses (6.8%); mild halo (9.7%); and, minor glare (10.0%).Long term risks of PRK beyond 3 years have not been studied. Note that the complete name for this ophthalmic laser is "SVS Apex Excimer Laser for Photorefractive Keratectomy (PRK) for the Correction of Mild to Moderate Myopia (-1.5D to -7.0D) with Low Astigmatism (<1.5D)."