Understanding Your Vision Prescription
An annual eye exam helps keep your eyes healthy and ensures the optimal vision correction; if it’s been more than a year since your last eye exam, schedule an appointment now. Below, InVision’s Dr. Toni Albrecht, OD, explains what those numbers and abbreviations on your vision prescription mean.
1. OD and OS
These measurements indicate the correction required for your right eye (OD, “oculus dexter“) and left eye (OS, “oculus sinister“).
2. Sphere (SPH)
The SPH, or sphere, measures the amount of lens power prescribed to correct nearsightedness or farsightedness.
Corrections for seeing clearly up close (nearsighted) have a negative value (for example -2.00). Those for distance (farsighted) 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)
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, which means the eyes have an oblong shape, like a football, instead of being perfectly round and smooth, like a ping pong ball. The irregular shape prevents light from focusing properly in the back of your eye, which can cause blurry or double vision, eye strain and headaches.
If your prescription has a Cylinder (CYL) 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.