September 09, 2019


Author Maxim Tourou / Category Architecture / Published: Apr-05-2018

It is the job of the optometrist or ophthalmologist to provide you with your eyeglasses prescription once you have completed the eye exam. By having your prescription you get all the pertinent information about the condition of your eyes as well as being able to order glasses online if you so desire.

However, your prescription may be full of terms, numbers and abbreviations that you may not be all that familiar with. After all, what exactly does OS, OD, CYL or SPH actually mean anyway? Here you will learn what all of the terms mean so that you can be best informed about your eyesight as well as understanding all the information necessary to order eyeglasses online.

The Terms Used in Eyeglasses Prescription

There are a number of terms that are used on your prescription and they start with OD, OS and OU. To understand these terms which are derived from Latin will help you know what your prescription actually means.

OD: Ocular Dexter – Left Eye
OS: Oculus Sinister – Right Eye
OU: Oculus Uterque – Both Eyes

Plus, while it may seem a bit odd that doctor’s put the information from your right eye ahead of your left eye, that is because when they face you they see your right eye first and then examine the left. Depending on your doctor or clinic, you may find that instead of using Latin phrases, they instead use LE and RE for Left Eye and Right Eye respectively.

SPH (Sphere): This announced the amount of lens power needed to correct the vision. The number associated with SPH will either have a “-“ or a “+” sign which indicates if the eye is nearsighted or farsighted respectively. Sometimes farsighted is simply indicated by the number alone.

CYL (Cylinder): This is the indication of the lens power needed to correct astigmatism. If you do not see a number in this column, then you have no astigmatism or it is so slight that no correction is needed. Like the SPH you will see a minus or plus sign to indicate either nearsighted or farsighted respectively.

Axis: This is used to describe the lens meridian if it has no CYL power to correct the astigmatism. The number 90 is the vertical meridian while 180 is the horizontal meridian.

Add: The added magnifying power that is used on the bottom part of a multifocal lens. This is used to correct presbyopia. The number is always a positive one and will usually range from .75 to 3.00 D and will be the same for both eyes.

Prism: The amount of prismatic power as measured in prism diopters (PD). This is used for the alignment of the eye itself. Very few eyeglasses prescription will contain this information.

A Typical Eyeglass Prescription

A standard eyeglasses prescription will contain unique information for each person, but it will appear in generally the same order with the associated terms.

OD: -1.00 SPH     +2.00 ADD     0.4 p.d. BD
OS: -2.00 -0.50 x 180     +2 ADD     0.5 p.d. BU

Here, the prescription is for a -1.00 D sphere that corrects the nearsightedness of the right eye. Not that there is no astigmatism for that eye and the doctor has added SPH to show the right eye is only being prescribed spherical power.

The left eye is -2.00 D for nearsightedness and added -0.50 D cylinder which will correct the astigmatism. The 180 is the axis which means that the CYL power is no applied to the horizontal plane while the vertical gets the added correction.

Since both eyes are being corrected for nearsightedness, the prescription contains a 0.5 prism diopter (p.d.). The BD indicates the prism is down for the right eye while BU is prism up for the left eye.

Prescriptions for Eyeglasses Only

Remember that all the terms used are for eyeglasses and not contact lenses. This is because contact lenses require additional information that is not included in standard eyeglass prescriptions. This is because although similar in nature, there are some important differences between eyeglasses and contact lenses.

While contact lenses sit directly on the eyes, glasses are actually a little further from the eye which means that the actual prescription is different in order to take that distance into account. Plus, there is additional information that needs to be included with contact lenses such as the following;

  • Base Cure of the Back Surface
  • Diameter of the Lens
  • Manufacturer and Brand Name

An accurate prescription for contact lenses can only be performed after the fitting and the doctor has fully evaluated your eyes in response to the lenses.

Get Your Eyeglasses Prescription

In 1980, the Federal Trade Commission enacted the Prescription Release Rule that requires eye doctors to give patients a copy of their prescriptions for eyeglasses at the end of the examination. The information also includes the refraction as well. The law allows you to go somewhere else and purchase glasses so that way you are not locked into a single source for getting new glasses.

In fact, your doctor will provide you the prescription whether you ask for it or not in order to protect themselves in terms of the law. They cannot charge you for releasing the prescription nor can they release the information to anyone else. In addition, they are still liable if their prescription is not accurate if you purchase the eyeglasses at another location. The penalties are fairly severe when eye doctors violate the law, so it would be highly unusual for you not to get the prescription included at the end of your eye exam.

You can take this information to another place to purchase your glasses or even buy eyeglasses online if you so desire. Many online sites will have the form ready to fill out so that you can put in the information and get the right lenses. In this manner, you can buy glasses online for a price that is the same or sometimes even less expensive than purchasing them from a local store.