You already know that an annual eye exam can help keep your eyes healthy and ensure the optimal vision correction, but do you know what those numbers and abbreviations on your vision prescription actually mean?
1. OD and OS
Abbreviations for the Latin terms oculus dexter and oculus sinister, these measurements indicate the correction required for your right eye (OD) and left eye (OS).
2. Sphere (SPH)
The SPH, or sphere, measures the amount of lens power prescribed to correct nearsightedness or farsightedness.
Corrections for nearsighted vision have a negative value (for example -4.00), while those for farsighted vision have positive values (i.e. +2.00). In general, the further your value is from 0, the worse your eyesight and stronger the correction.
3. Cylinder (CYL)
On your vision prescription, the cylinder (CYL) measurement corrects astigmatism. If your prescription doesn’t have a cylinder value, you either don’t have astigmatism, or it’s so slight that it doesn’t need to be corrected with lenses.
What is Astigmatism?
The majority of eyeglasses wearers have some degree of astigmatism. Instead of being perfectly round and smooth, like a ping pong ball, eyes with astigmatism have a more oblong shape, like a football. The irregular shape prevents light from focusing properly in the back of your eye, which can cause blurry or double vision, eye strain or headaches.
If your prescription has a cylinder value, it will also have an axis measurement. The axis value is between 1-180 and indicates the degree or angle of astigmatism, where 90° is the vertical center of your eye and 180° is the horizontal center.
5. Pupil Distance (PD)
Exactly what it sounds like, PD measures the distance, in millimeters, between your pupils. Pupil distance is an important part of your optical prescription and ensures your lenses are made specifically to give you the best possible vision correction.