So you have your eye examined by an eye doctor and prescription letter is right with you but having a hard time decoding the meaning. Well, just like you many other people wonder about the meaning of confusing numbers mentioned in the prescription letter and we can guarantee that majority of them don’t understand the jargons used in that paper. Although it does not matter much even if you do not understand but it’s good if do. Believe us it is not that hard and will give you the facts to discuss with experts.
Every prescription letter consists of certain abbreviations and variables like SPH, CYL, AXIS etc and numbers assigned to them. The numbers assigned to the variables SPH and CYL are measured in diopter unit.
In which unit do you measure the distance from your home to office? In Kilometers right?
|Spherical||Cylinder||Axis||Right Eye||Left Eye||Pupillary Distance|
Spherical (SPH) – This number denotes the level of farsightedness or nearsightedness. Bigger the digit, stronger the prescription and weaker the eyesight. Zero is considered as healthy and -2.0 is stronger than -1.0
Here, a negative number means that you are nearsighted and positive number means you are farsighted.
Cylinder (CYL) – If you see cylinder number in your prescription, it just means that you have something called astigmatism. But wait, this is not a disease but simply an inappropriate shape of cornea of your eyes. Most of the times people who have astigmatism are born with astigmatism. This can be better understood by imagining a “mirror house” at circus where objects in the mirror appear so funny. Either they appear too tall or too broad etc. When light enters into your eyes it falls at an inappropriate point at the back of your eyes because of that wrong shaped cornea, you find it difficult to view this beautiful world.
So, cylinder is just a feature of the lens to bend the light at a predefined degree to correct the vision.
AXIS (AX) – This is a necessary number mentioned in the prescription if you have astigmatism. The number specified in AXIS is measured in degrees and can be anything from 1 to 180. Needless to say that higher the number would not reflect a stronger prescription as it’s just a degree. This tells the eyeglasses maker where to position the lens in the frame to correct the astigmatism.
Pupillary Distance (PD) – This is the distance between the center of your both eyes. It is usually measured in millimeters. We have observed that not all prescription letters have this unit but you should ask your doctor to mention the same if you are above 40 years of age and have both nearsightedness and farsightedness. This number is very important if you want to wear progressive eyeglasses.