About excimer laser

In the early 1980s the Excimer Laser was first used to remove corneal tissue from the eye. Subsequently, Photorefractive Keratectomy (PRK) was developed. PRK was intially developed to correct myopia (shortsightedness), astigmatism (distorted image) and there is now a developing technique for the treatment of hypermetropia (longsightedness).

Superficial corneal scars and some corneal diseases can also be treated using the excimer laser (PTK). The most up-to-date procedure to correct vision is Laser In Situ Keratomileusis (LASIK), which is a combination of a device called a microkeratome and PRK with the excimer laser.

How the Laser works

The ultraviolet argon fluorine laser carries a large amount of energy called photons, which break the bonds between molecules when they hit human tissue.

A thin layer of molecules can be vapourized and removed with each pulse of laser in a very precise way. With multiple laser pulses, the central cornea can be sculpted to change the curvature and power of the cornea, that is, making a "steeper" myopic cornea flatter.

With each pulse, 0.25 microns of corneal tissue is removed. The removal of 10 microns of corneal tissue corrects one dioptre of myopia.

A person with 5 dioptres of myopia would require 150 laser pulses to remove 80 microns of tissue (approximately 10% of corneal thickness). This would take about 40 seconds.

For comparison, a human hair is between 50 and 100 microns thick.