What is Astigmatism?

I’m probably asked this question more than any other so here’s a little primer on how the optics of the eye work.

Let’s first go over how light rays behave as they enter the eye.

Normal EyeIn a normal eye, light rays enter the eye, are bent by the tear film, cornea, and lens, and then come to one point focus on the retina. The retina is where rods and cones pick up the light signals which are then transmitted to the brain via the optic nerve.

Nearsighted EyeIn a nearsighted eye, the light rays are bent too much and cause the point focus to land in front of the retina. The closer things are to the eye, the closer they focus to the retina so nearsighted people can see up close, but have trouble with far objects.

These eyes are corrected using minus power lenses to move the point focus so it lands exactly on the retina so this eye can work like the normal eye does.

Farsighted EyeA farsighted eye does not bend light rays enough so the point focus lands behind the retina. These eyes can see things far away, but have more difficulty with near objects.

For these eyes, a plus lens increases the amount of power of the eye and helps to bend light more. With this increased power, light can focus on the retina so this eye also begins to work like a normal eye.

Astigmatism occurs when the surface of the eye is uneven. Some light rays are bent more than others so there can be multiple points of focus on the retina. This results in a blurred image no matter if the person is looking at distant or near objects.

Slight AstigmatismIn the eye to the left, there is only a small amount of astigmatism so the brain may be able to put these multiple images together without causing blur or double vision.

Susbtantial AstigmatismHowever, when there is a lot of astigmatism, the light rays come to focus in points that are so far apart, the brain cannot put the image together. In this case, special lenses need to be made to correct all the different amounts of curvature on the eye’s surface. This can be done in eyeglass lenses, soft contact lenses, or in extreme cases, rigid gas permeable lenses.

At Family Eyewear Gallery, Dr. Lin utilizes all of these types of lenses, including custom made contact lenses to correct even the most unusual cases of astigmatism. If you have astigmatism and didn’t think you could wear contact lenses, schedule an appointment today to learn more about your eyewear options