What is astigmatism?

Astigmatism is an irregular curvature of the cornea or lens of the eye, which is usually corrected with glasses or contact lenses.  

What causes astigmatism? 

Regular astigmatism is very common. You are more likely to develop astigmatism if you have a family history of it. Less common causes of astigmatism include trauma to the eye, and previous eye surgery. Frequent eye rubbing, especially in an aggressive manner, can lead to a problem called keratoconus, which leads to irregular astigmatism. This is not a typical case of astigmatism and should be evaluated by an ophthalmologist. The only way to know for sure if you have astigmatism is to visit your ophthalmologist.  

What does astigmatism look like? 

To the patient, astigmatism can present as blurry vision. Some other signs and symptoms of astigmatism are headaches, distorted vision, and squinting your eyes in order to see more clearly.  

When looking at your glasses prescription, you may see one value, or you may see three. If you see one value, then you only have a sphere correction. This is often abbreviated in prescriptions as “sph”. If you see three values, this means you have astigmatism. 

Here is an example of a prescription without astigmatism (one value seen): 

Right eye:        -4.00 sph 

Left eye:          -4.00 sph 

Here is an example of a prescription with astigmatism (three values seen): 

Right eye:        -4.00 -1.00 x 180 

Left eye:         -4.00 -1.75 x 180 

It is important to note that the astigmatism value is always defined by a third number called an axis. In the case above, the axis is 180 for both eyes. You will never see an astigmatism prescription that does not have an axis associated with it. This is because the doctor needs to know exactly where the irregular curvature of the eye is to give you glasses or contact lenses to correct it. Depending on the type of machine your doctor uses, your astigmatism prescription can be either positive or negative.  

There are devices called corneal topographers in an eye doctor’s office that can actually show you what your astigmatism looks like, but it is not necessary to have a corneal topography in order to diagnose astigmatism. The vast majority of astigmatism is diagnosed based on your eye prescription alone.  

Do contact lenses or glasses help astigmatism? 

Glasses can correct astigmatism and are the most common treatment for astigmatism. If you wear contact lenses, there is some degree of astigmatism that can be corrected by the contact lens itself because it physically drapes over the cornea and provides a more regular surface. In higher degrees of astigmatism, this may not be the case and you will likely need to wear a toric contact lens. Regular astigmatism is more common than irregular astigmatism. Irregular astigmatism, like the type that occurs in keratoconus or from other eye diseases, is less common but also more complicated to treat. An ophthalmologist, specifically a cornea specialist, can often help in managing these cases.  

What should I do if I think I have astigmatism? 

If you think you have astigmatism, be sure to visit your eye doctor. They can properly evaluate you as well as monitor you to see if your astigmatism is getting worse or staying the same. They will also be able to assist you in getting glasses or contact lenses to help you see better.