Eyewear Prescriptions

How to Understand your Eyewear Prescription

After the examination, if necessary, your eye doctor will prescribe glasses or contact lenses to correct or improve your vision. The numbers on the prescription describe your eyesight measurement and eye condition. You will receive your eyeglass prescription at the end of your eye exam, and your contact lens prescription when your fitting is complete. Fitting contacts may involve more than one appointment.

Sample Doctor’s Prescription:

The numbers indicate the strength or power of the lenses prescribed, measured in units called diopters. If you have hyperopia (farsightedness), your sphere will be positive (+). If you have myopia (nearsightedness), your sphere will be negative (-).

Sphere Cylinder Axis
R.E. / O.D. -1.25 -2.50 90
L.E. / O.S. -0.75 -2.25 90
Reading Add +1.50

The above prescription means the patient’s right eye has 1 ¼ diopters of myopia (nearsightedness) with 2 ½ diopters of astigmatism. The axis refers to the orientation of the cylindrical curvature of the lens. The axis can be anywhere from 1 to 180 degrees, with 90 being the vertical meridian. The left eye has ¾ diopters of myopia, 2 ¼ diopters of astigmatism, with an axis of 90.

Bifocal prescriptions are indicated with numbers such as the “+1.50 add” as seen on the sample prescription. This means that the patient will need 1 ½ diopters of power for reading added to the distance correction.


The following are some terms and definitions to help you understand your prescription:

R.E. / O.D. Right Eye   L.E. / O.S. Left Eye


Test to determine the amount of the ocular refractive error and the best corrective lenses to be prescribed.

Visual Acuity

The measure of visual power, expressed as a fraction that is usually determined by one's ability to read letters of various sizes at a standard distance from a test chart.

The normal sight is 20/20. The first number is the distance (20 feet) from the eye chart. The second number is the distance from which a normal eye sees a letter on the chart clearly. Someone with a visual acuity of 20/20 can see certain sized letters at a distance of 20 feet. Someone with a visual acuity of 20/40 only sees letters at 20 feet that a normal eye is able to see at 40 feet.


How nearsighted (-) or farsighted (+) you are.


The type of curvature of the spectacle lens to help patients with astigmatism.


An irregularity in the curvature of the eye. It is usually due to the cornea being curved more in one direction than another.


The orientation of the placement of the cylinder for astigmatism correction. The axis can be anywhere from 1 to 180 degrees.

Myopia (Nearsightedness)

A refractive error in which parallel rays come to a focus in front of the retina, enabling a person to see distinctly only at near distances.

Hyperopia (Farsightedness)

A refractive error in which parallel rays come to a focus behind the retina, enabling a person to see better at far distances.


The gradual loss of the ability to focus at close objects with advancing age. This makes reading difficult. Onset usually occurs between 40 and 45.

Lens Types:

The following are some typical types of lenses:

Single Vision

Corrective lenses with only one focal length (power).


Lenses containing upper and lower segments, each with a different power.


Corrective lenses with three focal lengths.


An eyeglass lens that incorporates corrections for distance vision through midrange, to near vision (usually in the lower part of the lens), with smooth transitions and no bifocal demarcation line.


Lenses that fit directly on the cornea of the eye.

Talk to your eye doctor if you have questions or concerns about your prescription so that you fully understand the results and implications of the examination.

This document is provided for informational purposes only. Please consult an eye care professional about symptoms that may require medical attention and may or may not be covered by your medical plan and/or routine vision plan.

Sources: American Academy of Ophthalmology (AAO) -