Home » How to Read a Prescription

How to Read a Prescription

 

We understand that many look at their prescriptions and see only a confusing jumble of numbers, symbols, and abbreviations. The following guide will help you decipher this important information.

Here are some examples of how your prescription might look:
NO. 1:

 

 

SPH

CYL

AXIS

ADD

O.D.

-2.75

-1.25

180

+2.5

O.S.

-1.75

-1.50

175

+2.5

 

NO. 2:

 

 

 

SPH

CYL

AXIS

PRISM

Distance

O.D.

1.00

0.50 005

O.D.

 

 

O.S.

1.75

 

 

Near

O.D.

+1.50

0.25 005

+1.50

 

 

O.S.

+0.75

 

 

NO.3:

R: -2.50 / -1.25 x 178

L: -4.00 / -1.50 x 180

First, let’s translate the abbreviations.

O. D. : O. D. simply means 'right eye'. It is the short form of the latin term 'oculus dextrous'.
O. S. :
O. S. simply means -- you guessed it -- 'left eye'. It is the short form of the latin term 'oculus sinister'.

Sphere : The number under the heading 'sphere' is the main part of your prescription. The number itself denotes the strength of the lens as measured in diopters. A diopter is a unit of measurement that is simply the inverse of the focal distance of the lens as measured in meters. For example, if a lens has a strength of 2 diopters, then parallel light rays that pass through this lens will focus together at a distance of 1/2 meter (50 cm) away from the lens. If you are near-sighted (i.e. - you have trouble seeing far away but can see fine up close), then you can make a rough calculation of the strength of your glasses.

 

Cylinder : If there is no value under the cylinder heading, then you have a very simple prescription. If there is a value under this heading, then you have astigmatism. The majority of optometrists write the cylinder value with a minus sign in front while the majority of ophthalmologists (physicians who specialize in the eye) write the cylinder value with a plus sign in front. Regardless of which way this is written, your glasses will be made the exact same way -- these are just two different ways to write the same spectacle prescription. Like sphere power, the cylinder power is also measured in diopters.

 

Axis : As mentioned above, a special cylindrical lens is needed in order to correct astigmatism. Not only does the strength of the cylindrical lens need to be specified, but the lens itself must be rotated into a specific position in order to provide the proper vision correction. The axis represents the amount of rotation of the cylindrical lens in degrees ranging from 1 to 180.
Add (or add power) : If there is a value under the 'add' heading, then you have a bifocal (or Progressive) prescription.

 

 

Some other abbreviations you might see:

 

D.S. or DS = diopters sphere which indicates that you have only a sphere value and no cylinder value; therefore you need no correction for astigmatism.

 

D.V. = distance vision

N.V. = near vision, sometimes written as N.V.O.

O.U. = both eyes

X = axis

P.D. = pupillary distance

 

Further information

SPH / SPHERE

All prescriptions have this measurement and this indicates the strength of your prescription in increments of 0.25. It is measured in diopters for either nearsightedness (myopia) or farsightedness (hyperopia). The number is sometimes written without the decimal point. For instance, 150 is 1.50.

Often the + or – sign is written above the number, so please check and select these signs carefully. You might also find an infinity (∞) symbol, Pl or PL in the sphere column. When ordering your glasses please select the ‘infinity’ or ‘plano’ option in the drop-down menu. In the prescription example 3, -3.75 is the sphere value for each eye.

CYL / CYLINDER

If you have an astigmatism, your prescription will have a number in this column. The number should be between +/-4 and in 0.25 increments. It’s common for the cylinder value to be the same for both eyes.

For any cylinder value provided, there will always be a value for axis.

There’s a huge difference between a positive (+) and negative (-) cylinder, so pay close attention when ordering, and select the correct sign.

In prescription example 2, the person has a -0.25 cylinder value for both distance and near vision. Sometimes the optometrist will leave out the decimal point, and you might find the negative symbol written above the number and not before it.

If you find a ‘DS’ or ‘SPH’ in the CYL column, this means that you have no astigmatism and hence no cylinder value, only a sphere power in your prescription. In this case, select the ‘CYL none’ option in the drop-down menu.

In example 3, the person has a -1.25 cylindrical value in the right eye and a -1.50 cylindrical value in the left.

AXIS

If you have astigmatism, the axis value indicates where your astigmatism is located along your eye’s horizontal axis. Not all prescriptions have axis and cylinder values; however if you have astigmatism you should have both of these values on your prescription. The axis number will be between 1-180 degrees, and it should always be a whole number - there should be no decimal point.

In example 3, the person has an axis value of 178 in the right eye, and 180 in the left eye.

ADD / NEAR ADDITION

This value can be written anywhere on the prescription. It indicates the amount to be added to the SPH value for reading, intermediate glasses or computer work. If you can only find one ADD value, this means that your ADD is the same for both eyes. If you find two figures, then you have a different ADD value for each eye.

If your prescription has a completely separate column for ADD, this means that this measurement is for the lower or reading section of your bifocal lenses.

PRISM and BASE

The prism and base sections are usually left empty, as they are not commonly seen on most prescriptions. Prism is used to treat people with a muscular imbalance or other conditions like a squint or lazy eye. While the prism value refers to the displacement of the image through the lens, the base value refers to the direction of this displacement.

Please enter your prism and base information into the ‘Any extra information’ box when ordering online.

BALANCE

If there is little or no vision in one eye, the optician might write ‘balance’ on your prescription to ensure that your lenses are a similar weight and thickness for cosmetic reasons.

If you have this written on your prescription, please enter this information in the ‘Any extra information’ box.


Extra tips

  • For distance correction, most of the time the value under sphere is negative.
  • For reading-only correction, most of the time the value under sphere is positive.
  • Please ensure that you get the + or – symbol correct. This will make a huge difference to the accuracy of your lenses.
  • If some of the boxes on your prescription are blank (e.g. no CYL or AXIS or ADD values), leave those boxes blank when ordering.
  • If you have a value under “Near Vision” (N.V., N.V.O.) then enter the power in the BOTTOM half of the form and leave the ADD power blank or ("0.00").
  • For bifocal and progressive lenses, please check with your optometrist whether the Addition (ADD) value is for bifocals or progressives.
  • Sometimes optometrists will leave out the decimal point on the Sphere, Cylinder and Addition values. For example, -25 is understood as -0.25, and +175 is +1.75.
  • If you see a PAL note written on the prescription, then this simply indicates that your prescription is for PROGRESSIVE lenses.
  • Please be advised that we process a minimum of +1.00 and maximum of +3.00 for ADD powers.

If there is anything else on the prescription that you are confused about, please call or e-mail our Customer Service and we’ll be happy to assist you.