Lasik for Astigmatism
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.
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.
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.
Laser in-Situ Keratomileusis (LASIK) can be used to treat astigmatism with nearsightedness or farsightedness as well as “mixed” astigmatism. Astigmatism occurs when the shape of the cornea is more like that of a football, rather than spherical (like a basketball). 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. Next, the Excimer laser sculpts the internal corneal tissue to the correct refractive power in the “steep” axis by flattening the curvature of the exposed corneal tissue in that axis more than the other. Light rays are then more directly focused on the retina in both axis, thereby reducing the astigmatsim. 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 return to work within one to three days. As with any surgical procedure, individual results cannot be guaranteed and side effects and complications may occur.
Before your consultation to evaluate you for LASIK, we ask you to discontinue soft contact lens wear for two weeks prior to your visit. Hard or rigid gas permeable (RGP) lens wearers should discontinue contact lens wear for three weeks prior to their visit. This is to prevent errors in measurement (due to potential warpage of the cornea) which could lead to under or over-corrections after surgery.
Selected images copyrighted and licensed by Stephen F. Gordon