Lasik for Astigmatism
Laser in-Situ Keratomileusis (LASIK) can be used
to treat some cases of astigmatism. Astigmatism occurs
when the shape of the cornea is irregular, and not spherical in
shape. This causes light rays in one axis to not be focused on the
retina, resulting in blurred vision. LASIK uses the computer-controlled
precision of the Excimer laser to treat the inner tissue of the
cornea in one direction more than the other.
The procedure is done using eye drop anesthesia,
and while you may feel pressure, the technique is generally not
painful. First, an instrument known as a microkeratome makes a protective
flap in the outer layer of the cornea, at about twenty-five percent
of its depth from the surface. The Excimer laser sculpts the internal
corneal tissue to the correct refractive power by flattening the
curvature of the exposed corneal tissue in one axis more than the
other. Light rays are then more directly focused on the retina in
both axes, thereby reducing or eliminating the astigmatism. Astigmatism
and myopia or astigmatism and hyperopia are corrected simultaneously.
After a few minutes of drying, the corneal flap is laid back in
its original position. Due to the cornea's extraordinary natural
bonding qualities, stitches are usually not required. The surgery
is performed on an out-patient basis and most people usually
return to work the next day. As with any surgical procedure,
individual results cannot be guaranteed and side effects and complications
may occur.
What is Astigmatism?
In the normal eye, light travelling through the
cornea in both the horizontal plane (blue) and vertical (red) plane
is refracted (bent) the same, so that the image is properly focused
on the retina in the back of the eye. Vision is clear. With astigmatism,
(place cursor over image), an abnormal curvature of the cornea in
one direction causes light travelling in one plane, the horizontal
(blue) plane in this case, to be focused in front of the retina.
The light striking the retina through the horizontal plane is out
of focus on the retina and vision is blurred.
The Treatment
1. A thin flap of cornea is created and folded back.
2. Excimer laser reshapes the high axis (line) of the cornea.
3. The corneal flap is replaced over the treated cornea.
4.
The reshaped cornea now bends light to become focused on the
retina.
LASIK for Astigmatism Animation
The Result
Before LASIK treatment, light traveling in the horizontal meridian (in this case blue) is out of focus on the retina. After LASIK treatment (place cursor over image), the reshaped cornea (arrow) causes light to bend in such a way as to become focused on the retina. Vision is clear.
