Posted on September 08 2015
Astigmatism is a very common visual problem, with some studies showing between a quarter and a third of participants having the condition. However, many of those who have astigmatism don’t know what it is. Also, there are some individuals who may have astigmatism in addition to other vision conditions like nearsightedness or farsightedness.
Nearsightedness and farsightedness are relatively simple conditions to understand: for one reason or another, light waves are refracted by the eye in a way that their focal point is in front of the retina (nearsightedness) or behind the retina (farsightedness). Astigmatism is a little more varied and complex than the other two conditions, but it is similar in that problems arise because light waves are not refracted correctly by the eye. This is why nearsightedness, farsightedness and astigmatism are often grouped together and called “refractive errors.” There are a number of causes of astigmatism, but the most common one is due to the shape of the cornea, the outer part of the eye. In a normal, or emmetropic, eye, the cornea is shaped like a baseball. However, people with astigmatism may have irregularly shaped corneas, looking more like a football than a baseball. Due to this irregular shape, light waves entering the cornea are refracted irregularly and do not always hit the photoreceptors in the retina. In fact, light waves may be bent in more than one direction by the cornea. For someone with astigmatism, different areas and distances may be less clear due to the irregular refraction of the cornea. Astigmatism can also be caused by an irregularly shaped lens in the eye, which will result in refraction errors similar to an irregular cornea. There is also a type of astigmatism called irregular astigmatism that is usually caused by a scar on the cornea (perhaps from an injury).
If you have astigmatism, it will almost always result in some sort of blurred vision because the light waves are not exactly hitting the retina. This can result in headaches and eye strain when conducting visually-intensive tasks. A common trait for someone with uncorrected astigmatism is squinting. An eye-care professional can diagnose astigmatism through a variety of tests. In addition to the regular eye acuity test (using a Snellen eye chart), your eye-care professional may also use light to measure the curvature of your cornea with a tool called a keratometer.
Similar to other refractive errors, astigmatism is quite treatable. Glasses, contact lenses and refractive surgery are possible options for those with astigmatism. Since there are variations to astigmatism and degrees of severity, one type of treatment may be better suited for you. For many people with astigmatism, a type of external lens called a toric lens will provide the best vision correction. A toric lens will bend light differently depending on what angle light is passing through the lens. This will compensate for the irregular refraction of the cornea or crystalline lens of the eye and allow for clear vision.