Laser surgery
(PRK and LASIK) for refractive errors
What is Excimer laser?
Excimer laser is a far Ultra Violet (UV) light energy of wavelength 193
microns. It is invisible to human eye. This laser breaks the chemical
bonds within the molecules (photoablation) with minimal thermal damage
to the surrounding tissues. Thus it is very precise and can remodel the
cornea with an accuracy of more than a thousandth of a millimeter.
How does Excimer laser correct the
refractive error?
The effect of excimer laser on the cornea is very similar to grinding
of a glass lens to change its refractive power. In eyes with refractive
errors, excimer laser because of its high level of precision, can change
the shape of the cornea to change its refractive power to the desired
state and thus correcting the refractive error.
In
myopia, the
central part of the cornea is made flatter, and thus decreasing the
refractive power of the cornea and of the eye, and thus correcting the
refractive error.
Similarly in
hypermetropia,
the laser removes a ring of tissue from the peripheral part of the
cornea and thus makes the central part steeper and corrects the
refractive error.
As we know, in
astigmatism,
the cornea is more curved in one direction. Excimer laser can correct
astigmatism also by selectively ablating the cornea in the required
direction.
What is PRK?
In PRK the surgeon removes the surface layer of the corneal epithelium
over the area to be treated, and the excimer laser is applied to sculpt
the corneal stromal front surface to a new shape. The surface epithelium
of the eye normally heals by itself in 2-3 days for myopia treatment and
4-7 days for hypermetropia treatment.
