How to read an eyeglass or contact lens prescription
An eyeglass prescription has three parts:
- sphere
- Cylinder and axis
- The add
They are usually written with the right eye is listed first, and it is noted by O.D. The left eye is O.S.
1. Sphere determines nearsightedness or farsightedness. No sphere is noted as "plano".
- If the power is a plus (+) sign, it is farsighted.
- If the power is a minus (-) sign, it is nearsighted.
Prescription ranges: Mild prescriptions are in the range of plus or minus 1 to 3, while high prescriptions are over plus or minus 5 to 7.
2. Cylinder and axis represent the astigmatism correction.
Cylinder is power in a certain direction, and can be written as a plus or a minus power (ophthalmologists usually use plus, optometrists use minus).
Axis is the direction of the power. It is measured in degrees, from 1 to 180.
3. The add is additional power placed in a bifocal. This is always noted as a plus power, and is similar to a plus farsighted sphere power. This usually ranges from a +1.00 to +3.50.
Contact lens prescriptions are like eyeglass prescriptions.
However, they also state the following information:
- Name and type of contact lens being used
- Any tint in the lens
- base curve of the lens
- diameter
Sphere determines the power of contact lenses and it is typically just plus or minus.
Cylinder power is only used with special astigmatism correcting toric lenses (always a minus power for contacts) and an axis.
The base curve of the lens determines how tight the lens is on the eye. Normally it ranges from an 8.3 (tight) to a 9.0 (looser).
When Soft lenses are prescribed the base curve is typically noted as tight, medium, or loose and there may be only one diameter.
Hard lenses and gas permeable lenses are custom made and have offer many more choices.
Diameter is the width of the lens.