You’ve completed your eye test and have received a glasses prescription. Let’s decipher your prescription so you have a better understanding of what each number means. Below is a table that displays an example prescription.
OD = Right eye
OS = Left eye
Sphere
This number refers to whether you are long-sighted or short-sighted. These numbers move in 0.25 steps, and the higher the number, the poorer the vision is without correction.
Hyperopia
A positive (+) number indicates long-sightedness, otherwise known as hyperopia. This happens because as light enters the eye, it is focused behind the eye instead of directly on it. This can occur if the eyeball is too short or the cornea (the clear outer layer of the eye) has too little curvature.
- Eye strain
- Headaches
- Blurry near vision (although this can also affect your distance vision)
Myopia
A negative (-) number indicates short-sightedness, or myopia. As light enters the eye, it is focused in front of the back of the eye instead of directly on it. Myopia typically results from an eyeball that is too long or a cornea that has too much curvature.
- Blurry vision when looking at distant objects
- Squinting to see better at a distance
Cylinder
Cyl refers to the eye having astigmatism.
Astigmatism is a refractive error caused by an irregular shape of the cornea, lens, or eyeball shape. Instead of being like a smooth ball, it's more like a rugby ball or an oval. Because of this uneven shape, light enters the eye and doesn't focus properly. It’s like trying to shine a flashlight through a warped lens—the light doesn’t land in a single spot but instead spreads out or focuses in different places.
- Blurry or distorted vision both close up and/or far away
- Streaking of headlights at night
- Eyestrain and/or headaches
Not all people will have a cylinder part in their prescription, and it is possible to have only astigmatism without a sphere prescription.
Axis
Axis is a number from 1-180 which indicates the direction of the cylinder correction. As astigmatism causes light to scatter, the cylinder correction must have a direction to focus the scattered light in the correct place.
Add
Not all people will have an add. This is a number that is added onto the sphere number to create a separate prescription for reading. This means the prescription for distance is different from that for near (unlike hyperopia, myopia, or astigmatism where the single prescription can be used for distance and near).
People with an add typically have their near vision compromised. Generally, this begins at the age of 40 where people begin the process of presbyopia, and the muscles that normally focus for reading deteriorate with age. If you are young with an add, it may mean your muscles fatigue quickly and extra support is needed to sustain focus.