After you've had your regularly scheduled eye exam, the optometrist will hand you an eyeglasses prescription. At first the number and acronyms may seem like a foreign language but with a basic understanding of the terms you'll be able to pick the perfect pair of glasses.
OD and OS
OD is the abbreviation for the word oculus dexter, which means right eye in Latin. OC, on the flip side, is short for oculus sinister which means left eye. There may also be a column labeled OU which refers to both eyes or oculus uterque.
Sphere (SPH): The sphere is measured in diopters and measures the amount of lens power necessary to correct either nearsightedness or farsightedness. You can tell which one of the two you are by the either the + (farsighted) or – (nearsighted) symbol.
Cylinder (CYL): The cylinder specifies the amount of lens power necessary to correct astigmatism. If your eye doctor does not diagnose you with astigmatism then you either don't have one or it's so minor that no lens would make a noticeable difference. Sometimes the number in the column labeled cylinder has a plus or minus sign. The plus sign indicated farsighted astigmatism while the minus sign is indicative of nearsighted astigmatisms.
Axis: The axis can range from 1 to 180 and is used to describe the lens meridian to correct astigmatism. All prescriptions that have a cylinder power must also state the axis value.
Add: This refers to the magnifying power applied to multifocal lenses to correct presbyopia. Be aware that even if no (+) is noted, the power is always plus typically +.75 to 3.00 D.
Prism: The prismatic power is measured in diopters and is not very common in eyeglass prescriptions. Prism direction is noted using the four following abbreviations:
- BU= base up
- BD= base down
- BI= base in
- BO=base out
For Your Records
Based on the FTC Prescription Release Rule, your eye doctor is required to give you a copy of your eyeglass prescription. This measure was put in place as a way to protect the "portability" of prescriptions. In other words, you're freedom to purchase eyeglasses online or from any vendor of your choosing. If a doctor is found in contempt of this law, they are liable to a penalty of $10,000.