Laser in-Situ Keratomileusis (LASIK) can be used to treat some cases of regular 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.
Prior to performing Astigmatic LASIK (either as a primary procedure or in conjunction with myopia or hyperopia), a computerized corneal analysis is done to determine the magnitude and axis of the astigmatism. The surgery is performed under topical anesthesia, and while you may feel slight pressure during the keratectomy which generates a corneal flap, the technique is not painful. The flap is reflected and Excimer photoablation is performed to treat the astigmatism and any co-existant myopia or hyperopia. The corneal flap is then returned to its initial orientation and allowed to anneal in place for several minutes.
With the resulting flattening of the steepest axis to achieve a more spherical corneal surface (and the treatment of the myopic or hyperopic spherical component) , visual acuity is dramatically improved. Patients usually return to work the following day.
What is Astigmatism?
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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, is 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 unclear.
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The Treatment
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The outer surface of the cornea will be treated in such a way with the Excimer laser as to effectively "flatten" the cornea in the steep axis. In the example, the steep horizontal axis (blue), is ablated (shaded area) along this axis.
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| 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. |
The Result
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Before LASIK treatment, light travelling in the horizontal meridian (blue) is out of focus on the retina, in this case. 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.
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