How to Read Your Glasses Prescription

How to Read Your Glasses Prescription

After you finish your eye exam, the doctor should provide you with a written prescription for corrective lenses. With all the rows and blocks of numbers and letters, it can be tough to determine exactly what each of these things means for you. An eyeglass prescription doesn't need to be confusing. Read on to learn how to read your eye prescription so that you have a better understanding of what your eye doctor has discovered, and what it means for your eyesight.

OS & OD Meanings

Eyeglass prescriptions include the headings OS and OD, but what do these letters mean? The abbreviations are Latin and represent the OS or oculus sinister, which is the left eye, and the OD or oculus dextrus, which is the right eye. You may notice the letters OU on your prescription. If those letters are present, it refers to both eyes. The further away from the number zero on your prescription, the worse your eyesight is and the more intense vision correction is needed. You might also notice a plus sign or + in front of the number. This means that you are farsighted, while a minus sign means that you are nearsighted.

Prescription Measurements & Examples

The numbers on your eyeglass prescription represent something called diopters, which is what eye doctors use to measure the focusing power of your lenses. This measurement is typically abbreviated with a capital D. An example would be if your prescription shows a reading of -1.00, it means that you have one diopter of nearsightedness. The larger this number gets, the more severe the nearsightedness is. In addition to the intensity of the diopter measurement, these numbers will also determine how thick your lenses need to be. For example, a reading of +1.00 would mean thinner glasses and a milder form of farsightedness, while a +4 reading would mean thicker lenses and a more severe case.

Astigmatism Prescription Differences

If you have astigmatism, your eye prescription will be different. There should be three numbers included on these prescriptions: S x C x Axis. The letter S refers to the spherical part of your prescription, which refers to the intensity or degree of near or farsightedness that you have. The letter C refers to the cylinder, which may be listed as either a positive or negative number. This number measures the diopters of the degree of your astigmatism. In other words, the higher the number, the more intense your astigmatism is. This condition is when your cornea is shaped closer to a football than to a basketball.

The term Axis should also be present if you have astigmatism. This number will be between 0 and 180 degrees. It refers to the orientation of the astigmatism, and it helps to determine where the curve is occurring. Here's an example of a prescription for someone with astigmatism: -2.00 + 1.50 x 180, which means the person would have two diopters of nearsightedness, 1.5 diopters of astigmatism, and an axis or curvature of 180 degrees. Now that you know a little bit more about how to read your glasses prescription, you can understand where your eyesight currently stands. As always, ask your eye doctor if you have any detailed questions about your prescription so they can help clear up any confusion.