Have you ever wondered why your eye care provider spends so much time carefully examining your eyes? Although they are looking for diseases or conditions that can affect your vision during eye exa ...View Article
You are using an outdated browser. Please upgrade your browser to improve your experience.
Dictionary definition of astigmatism: A visual defect in which the unequal curvature of one or more refractive surfaces of the eye, usually the cornea, prevents light rays from focusing clearly at one point on the retina, resulting in blurred vision.
This is true, but the word astigmatism somehow sounds more serious than myopia or hyperopia to patients. Perhaps because the word “stigmata” often refers to the wounds of Christ from the crucifixion!
The unequal curvature of the refractive surface of the eye is usually the outer lens of the eye, the cornea, but it can also be the inner lens of the eye, so called lenticular astigmatism. Most astigmatism is in the cornea. The unequal curvature is like a spoon or a football, where the shorter axis is more curved than the longer axis. When light enters a perfectly curved lens it comes to a single point focus. Think of burning a piece of paper by holding a magnifying glass and focusing sunlight on a piece of paper
When light enters an astigmatic surface, there are 2 separate focal points and the more astigmatic the surface, the further these two points are apart and the more blurred the resultant image. Most eyes in fact have some degree of astigmatism so astigmatism can be myopic (both points focusing in front of the retina), hyperopic (both points focusing behind the retina) or mixed (one point if front to the retina and one point behind). In some eyes, the cornea is markedly distorted, or warped and the astigmatism is irregular, resulting in multiple points of focus that cannot be precisely focused with glasses and require hard contact lenses for best vision. Irregular astigmatism can be caused by warpage from over wearing of contact lenses or degenerative conditions of the cornea like keratoconus.
Regular astigmatism can be corrected by glasses, contact lenses or surgery. So most patients who have LASIK or PRK are able to correct both myopia and hyperopia and astigmatism. Some cases of irregular astigmatism can now be corrected by topographically guided PRK or LASIK.