Astigmatism is a refractive error that can prevent people from seeing objects up close or at a distance. This problem can affect the eyes differently and may cause objects to appear blurry.

What is astigmatism?

It occurs when the lens of the eye is not curved evenly, so the light entering the eye does not focus correctly on the retina. Essentially it means that the lens of the eye is shaped more like a football than a basketball. Sometimes it can develop after an eye surgery or eye injury. It is treated with glasses or contact lenses. In some cases, surgery can be used to resolve this issue.

What is the axis of astigmatism?

Astigmatism is measured in units of dioptres. However, in your prescription you may notice an axis box. This is an indication in which way the astigmatism is oriented. This helps your optometrist to prescribe corrective wear, as it can measure the light coming into the eye from different directions. It refers to the location where correction for astigmatism will be required on the lens.

How is the axis calculated?

There are two planes in astigmatism - one is a vertical meridian and the other a horizontal one. The axis of astigmatism is calculated by determining the difference between these planes. Dioptre is the way an optometrist measure the power correction required, whether that be for long or short sightedness. You may also notice another measurement on your prescription for cyl. This stands for cylinder and is the difference in power between the two planes of astigmatism. If there is no cyl in your prescription it means that either you have no astigmatism or that it is so slight it does not need to be corrected. It is also worthwhile noting that your prescription will be different for contact lenses and glasses, as the axis will change to reflect how close the lens is to your eye. Some people may find that glasses make the walls or floor appear to tilt. However, this feeling usually goes away when they get used to their new glasses. In cases of severe astigmatism this can take a week or so.

How does astigmatism change over time?

Astigmatism can change over time as it only reflects the shape of the cornea, or the front window of your eye.In some eyes it can change more than expected.

What does it mean when the axis of the cyl changes?

When the axis of the cyl changes, it simply means that the front shape of your eye has changed. A small change in this shape can often give a larger change in axis, so this is nothing to be concerned about, providing your eyes are healthy. It may even occur over what seems like a short period of time.Your optometrist will check the health of your eyes in an eyesight examination and will tell you if this reveals anything you should be concerned about. However, if you notice that the axis has changed dramatically (more than 90 degrees) you may want to clarify this with your optometrist, as a change this big is unusual.

Could the axis change from 180 to 10?

While this may seem like a big difference, it is important to note that a degree of zero is also written as 180.This refers to a change of 10 degrees, which is not a big shift if the cyl correction is higher. However, if you have a low cyl of 4 or lower, this adjustment could be critical.The cyl correction refers to the degree of astigmatism.