Many people are told that they have astigmatism during an eye exam, but are never given a sufficient explanation of what that means for their eyes and vision. The purpose of this post is to explain exactly what it means to have astigmatism and the various ways to manage it. Astigmatism refers to a discrepancy between how the eye focuses light in one direction, or plane, compared to a different direction. Most of the focusing devices, or lenses, that we are familiar with are referred to as "spherical lenses". This means that the lenses focus light the same way in all directions, regardless of the orientation of the incoming light.
Examples of this include a telescope, a microscope, or the human eye (provided the eye is not astigmatic). Think of a spherical lens as a perfect circular eye that is symmetric no matter which section you approach it from. Astigmatism occurs when the eye behaves as a non-spherical lens. A good way to imagine this is by picturing an eye that, instead of being spherical, is egg-shaped or oval shaped. The curvature of the lens changes depending on the section of the lens that you are referring to. This difference in curvature means that light is not focused in the same plane as it reaches the retina.
The solution to this problem involves changing the way that light is focused along one curvature so that it matches the other, different curvature. Think of the egg example. Common ways to do this involve adding what is referred to as a cylinder lens to our glasses or using a contact lens to correct the astigmatism. Special contact lenses (known as "toric" lenses) fit in a particular fixed orientation over the surface of the eye in order to normalize the curvature responsible for focusing light into the eye. Refractive surgery such as LASIK or PRK can also be used to correct astigmatism by restoring uniform spherical curvature to the surface of the eye. Finally, special lens implants during cataract surgery called toric IOLs can be used to treat astigmatism surgically.
I hope this helps to increase your understanding of this commonly referred to but commonly misunderstood concept. Thanks for visiting our blog!
Adam Hart MD