I recently got my eyes examined and the optometrist says I have astigmatism. What is this?
For us to see clearly, light from objects in our field of vision hits the eye and is refracted (bent) so that it eventually focuses on the retina. The cornea, the front surface, refracts light first, then the lens which is behind it. The light then travels through the globe and focuses on the retina, the inner surface of the eyeball. The first surface the light hits, the cornea, is usually spherical – round like a tennis ball. However, in most cases it’s not perfectly round, it’s a little elliptical, egg/American-football shaped. It has a steep curve and a flatter curve. This means that the light is refracted into two points on the retina instead of one, and you will see a blurry image, both for distance and near. This condition is called astigmatism. If you look at a star at night, instead of it looking round, it may look oval shaped, or as if it has a tail, depending on the amount of astigmatism you have. Most people have small amounts of astigmatism.
If the cornea is round, but steeper than normal, the light will be bent too much and the light will focus in front of the retina. This condition is called myopia, or nearsightedness. If the cornea is round but flatter than it should be, the light will focus behind the retina, called hyperopia or farsightedness. So, you can see, you can be nearsighted alone if the cornea is spherical, but be nearsighted with astigmatism if the cornea is elliptical. With high amounts of astigmatism, patients have to be warned that things will look high and low or may appear tilted when they first get their glasses. Most astigmatism is corneal. In a few cases, the curvature of the lens is irregular and this leads to lenticular astigmatism.
Can I wear contacts with astigmatism?
Yes, contact lenses for astigmatism have been available for many years. Initially it was only hard/gas permeable contacts that would give good vision, but subsequent to that, special soft contacts, called toric lenses, that correct for the astigmatism became available. These lenses cost more than the regular spherical lenses because of the complex manufacturing process. A person who just has myopia, needs a spherical contact because the cornea is round all around. However, the person with the irregular cornea needs a contact lens that corresponds to the areas of irregularity and these lenses are specially manufactured and are thus more expensive. Your optometrist may also explain that these lenses may be a little more difficult to fit than spherical lenses, but you should achieve good vision nonetheless. Up until the last 10 years or so, patients with high amounts of astigmatism could not get toric lenses in their power, but now several companies offer custom-made lenses.
