LASIK or PRK Can Correct Astigmatism. Oblique Astigmatism Patients Have Greater Visual Difficulty Prior to LASIK or PRK than Patient with Other Forms of Astigmatism.
Astigmatism occurs when the cornea is football shaped. If the football is held tip to tip in the horizontal, then the steep curvature of the football is vertical. This is called “with the rule” astigmatism. This phrase is used because this is the most common orientation of astigmatism.
If the football is rotated 90 degrees, then the steep axis is in the horizontal. This is called “against the rule” astigmatism. This is the second most common type of astigmatism.
If the football is tilted at an angle, then the steep axis is either at 45 degrees or 135 degrees. This is called “oblique astigmatism.”
A new study from Japan, just recently published in the August issue of the Journal of Cataract and Refractive Surgery, compares vision in patients with each of these three categories of astigmatism. Patients who were in the study never had undergone LASIK or any other corrective eye surgery — this was a study of the impact of astigmatism on a patient’s vision.
The eyes of 38 healthy volunteers with no eye disease other than refractive errors were studied. Both distance and near visual performance was measured after nearsightedness or farsightedness (but not astigmatism) was corrected using lenses. Results showed that patients with “with the rule” astigmatism and “against the rule” astigmatism” had significantly better near and far vision than patients with “oblique astigmatism.”
Of course, contemporary LASIK and PRK are capable of complete correction of all three forms of astigmatism. This study, however, shows that patients with oblique astigmatism have a greater difficulty with their vision both at near and at distance before it is corrected.
See Also
Effect of Axis Orientation on Visual Performance in Astigmatic Eyes
Eyes with oblique astigmatism have worse near and far vision than eyes with with the rule astigmatism or against the rule astigmatism
Journal of Cataract and Refractive Surgery
Journal of Cataract and Refractive Surgery Website
Oblique Astigmatism of the Reduced Schematic Eye with Elliptical Refracting Surface
Coddington’s equations are explored for use in describing oblique astigmatism in a model eye
Aspherical Surfaces Used to Minimize Oblique Refractive Error
A review of using corrective lens techniques for correcting oblique refractive errors of the eye
Optical Oblique Astigmatism of the Human Eye
A technical discussion of the optics of oblique astigmatism in the human eye.
Astigmatism
Three common types of astigmatism and how to correct them are discussed in this All About Vision post.