One of the most common questions we answer is what all the numbers on one’s eyeglass prescription mean.
After you get an eye exam, you have the right to request your prescription from your doctor and you can get your glasses anywhere you want so it's important that you have some understanding on what those numbers mean.
In this article, we will go over the your eyeglasses prescription and help you interpret those numbers.
The first letters you will see if the letters O.D and O.S. Make sure you do not confuse OD to “once daily” which is a common meaning for O.D in prescription.. OD on a glasses prescription stands for Ocular Dexter or right Eye in Latin. O.S means Ocular Sinister which means the left eye. Sinister means “left”in Latin.
When you look at your prescription, the first column is your distance prescription. It can be either negative or positive. If it’s a negative prescription, you suffer from Myopia or nearsighted or shortsighted which is the most common vision problem. It would go more negative as your prescription increases and things get blurrier when you do not wear corrective glasses. Also the lens you will get will be thicker as the negative number gets higher.
If you have a + prescription in the first column, that means you have hyperopia or far-sighted or that you see thing clearer far than near. This is not as common as myopia and shouldn’t be confused with one’s “add” power or reading prescription which we will discuss later.
The second column that says “cyl” is short for cylinder and it’s your prescription to correct for your astigmatism. Astigmatism is when your cornea is in an irregular shape like a football and light gets to the retina in a distorted manner. The cly is typically a negative number and comes with a Axis amount that is put in the third column of your prescription.
Not everyone has Astigmatism, only about 33% of the people have this disease and it usually occurs because of genetics or injury….not because you read in the dark too much or watch too much TV.
The fourth column your reading prescription or “add” power. The medical term for needing reading glasses is called presbyopia and that number is added to your distance prescription in the first column to make your reading prescription. You typically see this show up when you’re around 40 years old or when you find it harder to read, look at your cell phone, work on your computer, or view things close at low light. When that happens, it’s time to ask your optician for progressive lens, or a lens that progressives from your distance prescription to your reading prescription as your eyes move from up to down.
The last and most important part of your eyeglasses prescription: the expiration date.
An optician would not dispense you a pair of glasses or sell you contacts with an expired RX for the same reason. There is more to an eye exam than just the RX, its about the overall eye health and just like your overall health, that needs to be inspected on a yearly or once every two year basis based on the judgment of your eye doctor.