What does it mean to have astigmatism?
So you’re one of the many people with astigmatism, but are you one of the few who actually knows what that means? Astigmatism is one of, if not the most misunderstood eye problem around. For starters it is commonly mistaken for a disease or a vision health problem when in actuality it is simply a problem with how the eye focuses light.
Astigmatism is caused by an irregular shaped cornea, the clear, round dome covering the eye’s iris and pupil. Or it may be caused by the curvature of the lens inside the eye. Whichever the cause it ends up preventing light from focusing properly on the retina which is called a refractive error. When the cornea has an irregular shape, it is called corneal astigmatism. When the shape of the lens is distorted, you have lenticular astigmatism. As a result of either type, your vision for both near and far objects can appear blurry or distorted. Other symptoms include eyestrain, headaches and eye discomfort.
Astigmatism is very common. In most cases, people with astigmatism are born with this condition. The reason why corneal shape differs from person to person is still unknown, but the likelihood of developing astigmatism is inherited. On occasion astigmatism can develop after an eye disease, injury or surgery.
Diagnosing astigmatism is easily done by your eye doctor with a comprehensive eye examination. There are a few test the doctor may choose to perform to measure how the eyes focus light and may determine the power of any optical lenses needed to compensate for reduced vision. This examination may include:
Visual acuity—As part of the testing, you'll be asked to read letters on a distance chart. This test measures visual acuity, which is written as a fraction such as 20/40. The top number is the standard distance at which testing is done, twenty feet. The bottom number is the smallest letter size you were able to read. A person with 20/40 visual acuity would have to get within 20 feet of a letter that should be seen at forty feet in order to see it clearly. Normal distance visual acuity is 20/20.
Keratometry- A keratometer is the primary instrument used to measure the curvature of the cornea. By focusing a circle of light on the cornea and measuring its reflection, it is possible to determine the exact curvature of the cornea's surface. This measurement is particularly critical in determining the proper fit for contact lenses. A more sophisticated procedure called corneal topography may be performed in some cases to provide even more detail of the shape of the cornea.