Astigmatism

Refractive Eye Conditions

Through the years, astigmatism has actually developed a not-too-nice name for itself. In early years, correction for astigmatism was difficult and those who had astigmatism were pretty much out of luck when it came to clear vision. But thanks to advances in contact lens, spectacle, and laser surgery technology, astigmatism really isn't a problem these days.

What many people don't realize is that astigmatism is actually a very common eye condition: every single person probably has a little bit of astigmatism. Just as our face is not entirely symmetrical, our cornea is not perfectly spherical: we are simply built that way. Mild astigmatism, however, is so minor that your optometrist may not even find it necessary to acknowledge it.

The best way to describe astigmatism is to imagine the shape of a football (American football) compared with the shape of a basketball. A football has two different curvatures to it: one that is longer and flatter while the other is shorter and much more curved. Like the cornea of a person with astigmatism, the football is far from being perfectly spherical – one meridian is steeper or flatter than the other. Imagine that the basketball has two meridians as well – both are identical (there is no place where one curve of the basketball is flatter or steeper than another curve): a basketball is perfectly spherical, like simple myopia, hyperopia, and emmetropia. Though this example is very extreme compared with the cornea of the eye, it illustrates the difference between astigmatism (the football) and simple myopia (nearsightedness), hyperopia (farsightedness), and emmetropia (no glasses or contacts needed).

Figure: Astigmatism. Courtesy of EyeAtlas.com.

The difference in curvatures of the eye leads to a difference in focusing power of the lens and cornea, so that light isn't focused onto a single point on the retina. Resulting vision is clearer in one meridian (eg. horizontal) and blurred in the other meridian (eg. vertical).

While in most cases, astigmatism is due to an irregularly shaped cornea, it is possible that it could be due to an irregularly shaped crystalline lens. Regardless of the cause, however, astigmatism can be corrected with glasses, contact lenses, and laser eye surgery.

Signs & Symptoms of Astigmatism

Most people who have only minor astigmatism may not even notice that they have it. If any, symptoms would include slightly blurred vision (which is worse in one meridian than the other) or distorted vision. More severe forms of astigmatism can be problematic as vision can be extremely distorted and blurred, leading to headaches and eyestrain. Both children and adults can have astigmatism, but children are much less likely to complain about its symptoms (they consider it to be normal) so regular eye exams are important.

Diagnosis of Astigmatism & Astigmatism Treatment

Astigmatism is determined in an eye exam. Your optometrist will determine just how much astigmatism you have and then whether or not it needs to be corrected. For minor astigmatism, soft contact lenses work just as well as eyeglasses. For severe cases of astigmatism, hard contact lenses may be better. Soft contact lenses that correct for astigmatism are very popular and are known as toric contact lenses. Laser eye surgery is an option for many people with astigmatism. Discuss laser surgery options with your eyecare professional to determine if it is right for you.

Do I Have Astigmatism?

How do you know if you have astigmatism? If you've got your prescription handy, take it out and have a look. Does it look a little something like this: -2.00 / -1.00 x 090 ? If so, then you have astigmatism. Any prescription that has three parts to it rather than 1 part (eg. -2.00 only)is a prescription with astigmatism. The first part of the above prescription describes the spherical power (in this case, -2.00 Diopters of myopia). The second part (-1.00) describes the amount of astigmatism. The third part (090) describes the axis – measured in degrees - along which the astigmatism occurs. Learn more about how to read a contact lens prescription.

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