Astigmatism is a term used by optometrists to describe a prescription for one eye that needs two powers to bring it into focus. It is not a disease or something that will make you go blind, but it can make things blurry at distance and at near.
Most people are familiar with the terms “near-sighted” and “far-sighted.” In the eye care world we use the term “myopia” for near-sightedness and “hyperopia” or “hypermetropia” for far-sightedness. These terms are used to describe the power (+ or -) of the lens needed to make you see clearly.
If your prescription needs only one power to bring your eye into focus then you can think of it as being simple. So if your prescription has a number like -4.00, then you have simple myopia. Similarly, if you have a prescription of +2.25, then you have simple hyperopia.
If you have an astigmatism in your eye, then you have two powers that need to be corrected for you to see clearly. Having an astigmatism in your eye is our way of describing a compound prescription. Instead of just one simple power like we described earlier, there are two powers together. Depending on your prescription, you can have myopia with astigmatism or hyperopia with astigmatism.
A common example optometrists use to describe astigmatism to patients is the difference between a basketball and a football. A basketball is nice and round, and has only one curve for the entire ball. You can think of that curve as a lens power. A basketball is a good example of a simple prescription. A football, on the other hand, has two curves. This is like an eye that has two powers or an astigmatism.
Astigmatism is not an eye disease, but rather a term we optometrists use to describe a compound prescription in one eye. So don’t be alarmed if your optometrist tells you that you have some astigmatism in your eyes. You are not alone – I have an astigmatism in both of my eyes and I see extremely well!
~Ranjeet S. Bajwa, OD, FAAO
California Optometric Association