How to read an eyeglass prescription?

How to read an eyeglass prescription

You've just had your eye exam and the optometrist or ophthalmologist has given you a prescription for glasses. He or she probably told you that you were nearsighted or farsighted, or that you might have astigmatism.

But what do all those numbers on your eyeglass prescription mean? What do the abbreviations R.E, L.E, SPH and CYL mean?

This article will help you decipher all the elements of the prescription and help you speak more knowledgeably with your eye care professional when shopping for glasses.

 

 

What do ER and EL mean?


The first step in understanding the eyeglass prescription is to know what ER and EL stand for. These are the abbreviations for right eye and left eye, respectively.

The prescription for eyeglasses may also have a column labeled AO. This is the abbreviation for both eyes.

On the eyeglass prescription, the right eye (OD) information comes before the left eye (OI) information. Eye doctors prescribe prescriptions this way because when they are in front of the patient the first thing they see is the patient's right eye on the left and then the patient's left eye to the right of them.

 

 

 

More terms in spectacle prescribing
The spectacle prescription also has other terms and abbreviations, among them:

Sphere (Sphere - SPH).

Indicates the amount of lens power, is measured in diopters (D) and is prescribed to correct nearsightedness or farsightedness. If the number under this heading has a minus sign (-) you are nearsighted; if the number has a plus sign (+) or is preceded by neither a plus sign (+) nor a minus sign (-), then you are farsighted.

The term 'sphere' means that the correction for nearsightedness or farsightedness is 'spherical' or equal in all meridians of the eye.

 

Cylinder (CYL)

Indicates the amount of lens power for astigmatism correction. If nothing appears in this column, you either have no astigmatism or your astigmatism is so mild that it is not really necessary to correct it with your spectacle lenses.

The term 'cylinder' means that the lens power that is added to correct astigmatism is not spherical, but is carved so that no curvature has been added to a meridian and that the meridian perpendicular to that meridian contains the maximum power and curvature of the lens to correct astigmatism.

 

The meridians of the eye are determined by superimposing a protractor on the front surface of the eye. The 90 degree meridian corresponds to the vertical meridian of the eye and the 180 degree meridian corresponds to the horizontal meridian.

Axis

Describes the meridian of the lens that does not contain the cylinder power to correct astigmatism. The axis is defined by a number from 1 to 180. The number 90 corresponds to the vertical meridian of the eye and the number 180 corresponds to the horizontal meridian.

If the eyeglass prescription includes the cylinder power, it should also include the value of the axis, which follows the right side of the cylinder power and is preceded by an "x" when handwritten.

The axis is the meridian of the lens that is 90 degrees from the meridian containing the cylinder power.

Addition (ADD)

This is the magnification power that is added to the bottom of multifocal lenses to correct presbyopia. The number listed in this section of the prescription is always positive (+) power, even if it is not preceded by a plus sign (+). Generally, it ranges from +0.75 D to +3.00 D and will be the same power for both eyes.

Prism

This is the amount of prismatic power. It is measured in prismatic diopters and if the prescription is handwritten, a triangle is drawn in superscript. It is prescribed to compensate for eye alignment problems. Only a small percentage of eyeglass prescriptions include prisms.

Sphere power, cylinder power and addition power are always expressed in diopters. They are in decimal format and are usually written in quarter diopter (0.25 D) increments. Axis values are integers from 1 to 180 and indicate only the meridional location and not the power.


Additional information

In order to give you the most comfortable vision correction possible, the eye doctor may also recommend specific lenses in the eyeglass prescription, such as anti-reflective coating, photochromic lenses or progressive lenses.