Your vision prescription is a record of your eyesight and the level of correction that is needed. In particular, the CYL and AXIS components of your prescription relate to the level of astigmatism in your eyes, a refractive error that means the front surface of one eye isn't completely round. This can cause problems affecting focus, and should be corrected to provide improved vision.

What do the AXIS and CYL parts mean?

The CYL part of your prescription stands for cylinder and this indicates the amount of lens power needed to correct your astigmatism. If there is nothing written down under this section that means you have no astigmatism or it is so moderate that correction isn't needed. The number written in the CYL section can be negative or positive. Figures further away from zero indicate a higher level of astigmatism. Meanwhile, the AXIS will be a number ranging anywhere between 0 and 180 degrees. This is further information about your astigmatism and details its orientation - essentially, describing exactly where the difference in the eyeball's curvature is. If you don't have any astigmatism this section will also be empty. AXIS values can go up in increments of half a degree, one, five or 10 degrees.

Changes in these values

Adults are recommended to get their eyes tested every two years, and during these examinations your optometrist will also assess you for astigmatism. If you compare your current prescription to an older one you may notice that your AXIS and CYL measurements have changed slightly. This is not uncommon, as eyesight can undergo several changes throughout one person's lifetime. As long as your AXIS and CYL measurements have been taken correctly, it should give you no cause for concern. However, if you notice a very dramatic change in these values it's important to talk to your optometrist about it so they can advise you on whether you will need a new pair of glasses to accommodate for the shift. While a dramatic shift in your CYL and AXIS numbers might be alarming, in most cases this won't cause any serious injuries or impacts other than a change in your level of vision correction. As long as your eye is healthy and there are no other underlying conditions or problems, a big change in your astigmatism level isn't threatening to your health.