The laser that is used during LASIK laser eye surgery is both painless and invisible. It can’t be seen because it is outside the visible spectrum of light. A patient from Santa Barbara recently told me her main concern about having LASIK was that she did not want to see the laser “coming at her” during the laser eye surgery. It turns out she had nothing to worry about: the laser is both painless and invisible. You can’t see it because it is outside the visible spectrum of light.
The excimer laser used in LASIK and PRK laser eye surgery simply is composed of parallel rays of light being use to precisely delivery energy to the eye in order to change its focus.
Light itself is a form of energy known as “electromagnetic energy.” Electromagnetic energy is waves of energy that appear differently depending on the wavelength of these waves. One extreme of the electromagnetic range ( or “spectrum”) is below radio waves, waves of energy which have very long wavelengths. On the other end of the electromagnetic spectrum are energy waves with very short wavelengths such as gamma rays. Wavelengths that we generally consider to be part of the electromagnetic spectrum can range from being as long as miles to as short as the size of an atom.
Light is the part of the electromagnetic spectrum that we are most directly familiar with because it is the part our eyes can sense visually. Light itself, since it is part of the electromagnetic spectrum, varies in appearance based on its wavelength. You probably are familiar with light passing through a prism or in a rainbow, in which case you can see light being displayed along its part of the electromagnetic spectrum. The light appears in the pattern of red, orange, yellow, green, blue, violet because red light has the longest wavelength, followed by orange, then yellow, all the way to violet, which has the shortest wavelength. The human eye can only perceive electromagnetic radiation with wavelengths between 760 nm and 380 nm. We see this energy as light. Red light has a wavelength of approximately 700 – 760 nm (nanometers) while blue/violet light has a wavelength of approximately 380 – 420 nm.
The light energy in the excimer laser that is used to reshape the cornea in LASIK or PRK laser eye surgery, by contrast, has a wavelength of only 193 nm. It is therefore far shorter in wavelength than visible light. The human visual system simply cannot perceive light energy in this wavelength range. For this reason, the laser light is completely invisible as it approaches your eye during surgery.
During LASIK surgery, you are asked to look at a flashing red light. This flashing red light is not itself a laser — it is simply a “target” to look at during surgery. It flashes only because studies have shown it is easier to continue to pay attention to a flashing — rather than a sold — light. A numbing drop is placed in your eye and a lid hold is placed to keep you from blinking. In this way, your eye is numb — so it doesn’t have the urge to blink — and the lid holder keeps it from blinking anyway. As you look at the red light, the computer guided laser painlessly reshapes your cornea, and you cannot see the laser since the light is outside the range of visible light. If your eye should move during surgery, the invisible laser can follow your eye using computer guided tracking systems based on military missile tracking technology. Typically, the laser treatment time is between 15 and 30 seconds. You do not see anything scary and you do not feel the laser at all!
See Also
FDA-Approved Lasers for PRK and Other Refractive Surgeries
FDA website discussing various lasers approved for PRK and LASIK.
Excimer Laser Refractive Surgery
Discussion of the basics of LASIK and PRK laser eye surgery using the excimer laser.
The 25TH Anniversary of Excimer Lasers in Refractive Surgery: Historical Review
A excellent review of the principles and practice of excimer laser refractive surgery, including LASIK and PRK.
Refractive Laser Surgery: An In-Depth Look at LASIK and a Brief Overview of PRK, epi-LASIK, and LASEK
An American Academy of Ophthalmology discussion of LASIK, PRK, epi-LASIK, and LASEK.
City of Santa Barbara
Website for the City of Santa Barbara, CA.
Custom LASIK or Wavefront LASIK: Individualized Vision Correction
All About Vision discussion of LASIK laser eye surgery.