How to Read Your Eyeglass Prescription

How to Read Your Eyeglass Prescription

When you look at your prescription for eyeglasses, you will see numbers listed under the headings of OS and OD. They are Latin abbreviations: OS (oculus sinister) means the left eye and OD (oculus dextrus) means the right eye. Occasionally, you will see a notation for OU, which means something involving both eyes. In general, the further away from zero the number on your prescription, the worse your eyesight and the more vision correction you need. A plus sign in front of the number means you are farsighted and a minus sign means you are nearsighted. These numbers represent diopters, the unit used to measure the correction, or focusing power, of the lens your eye requires. Diopter is often abbreviated "D."

For example, if your prescription says -1.00, you have one diopter of nearsightedness. This is a fairly mild amount of nearsightedness. If you are -4.25, that means you have 4 and 1/4 diopters of nearsightedness. This is more nearsighted than -1.00, and requires stronger (thicker) lenses. Similarly, +1.00 would be a small amount of farsightedness and +5 would be more.

For people who have astigmatism, there will be three numbers in your prescription. The general form for writing these numbers is S x C x Axis

The S refers to the "spherical" portion of the prescription, which is the degree of nearsightedness or farsightedness discussed above.

The C refers to the "cylinder" or astigmatism, and can be a negative or a positive number. It measures in diopters the degree of astigmatism that you have. The bigger this number, the more astigmatism you have. Astigmatism most often is caused by a cornea that is shaped more like a football than a basketball.

The Axis is a number anywhere between 0 and 180 degrees. It reveals the orientation of the astigmatism. It is not enough to specify how much astigmatism there is; you have to know where the difference in curvature is taking place.

Here are two examples of what prescriptions for eyes with astigmatism could look like:

-2.00 +1.50 x 180

+3.50 +3.00 x 45

The first prescription means that the person has 2 diopters of nearsightedness with 1.5 diopters of astigmatism and an axis of 180 degrees.

The second prescription means that the person has 3.5 diopters of farsightedness, 3 diopters of astigmatism and an axis of 45 degrees.

https://www.webmd.com/eye-health/how-read-eye-glass-prescription

HOW TO READ YOUR EYEGLASS PRESCRIPTION

You just finished your annual eye exam and with prescription in hand, you’re thinking about what kind of cool eyeglasses to try. Have you ever looked at all those numbers and letters and wondered what exactly do they mean? Whether you’re a longtime glasses wearer or a newbie, knowing how to decipher your prescription will give you a better understanding of what the eyeglass prescription could say about your vision and overall health.

YOUR EYEGLASS PRESCRIPTION DECODED

Your eyeglass prescription is typically written in a grid like the one below, using a combination of terms, abbreviations, and numbers. Usually you’ll see these abbreviations along the left side:

O.D. stands for oculus dexter, meaning right eye.
O.S. stands for oculus sinister, meaning left eye.
O.U. stands for and oculus uterque, meaning both eyes.

Then along the top, you may see this lingo. These abbreviations reflect the measurements of specific aspects of your vision, and can be pretty confusing at first.

SPH(or Sphere) indicates the eyeglass prescription power, or how strong your lenses need to be to correct your vision. For an indicator of how much magnifying power is needed in a bifocal or progressive lens to correct your vision problems, look for ADD.

CYL (or Cylinder) indicates astigmatism, a condition where the cornea is irregularly shaped causing blurred or distorted vision. It also tells the lens strength needed to fix it.

AXIS describes the degree and direction of your astigmatism.

ADD is added magnifying power in the lower part of a multi-focal lens. It’s used to correct presbyopia which is the inability to focus on close objects.

EYEGLASS PRESCRIPTION CHART

MAKING SENSE OF THE NUMBERS

Your glasses prescription includes a number for every aspect of your vision that needs correction. When learning how to interpret your prescription, keep in mind that usually the further from zero the numbers are, the more correction you need.

A plus or minus sign in front of your glasses prescription number is shorthand for
near or farsightedness.

+ means you’re farsighted or have trouble seeing things close up.
- means you’re nearsighted, or struggle with seeing far away.

IS YOUR RX (PRESCRIPTION) SINGLE VISION OR MULTI FOCAL?

Single and multi-focal eyeglass prescriptions will look different.

If your vision correction is single vision, that means your lens power corrects for nearsighted or farsighted, but not both. The ADD column (which stands for additional magnifying in a multi-focal Rx) is blank in the sample Rx above. If you’ve got an eyeglass prescription for bifocal or multi-focal/progressives, your lens power corrects for near, far, and sometimes intermediate range vision. You’ll have a number in the ADD column.

No matter what your eyesight numbers are, or whatever kind of vision correction you need, it’s good to have your eyes examined about once a year to make sure your prescription for eyeglasses or contact lenses is up to date.

https://www.lenscrafters.com/lc-us/vision-guide/glasses-prescription

How To Read Your Eyeglass Prescription

By Gary Heiting, OD

See also: The basics of eyeglasses • What's new in eyeglass lenses • Understanding your contact lens prescription

So, you've just had an eye exam and your optometrist or ophthalmologist has given you an eyeglass prescription. He or she probably mentioned that you are nearsighted or farsighted, or perhaps that you have astigmatism. (If that's not the case, and you need to see an eye doctor, click here to find one near you.)

But what do all those numbers on your eyeglass prescription mean? And what about all those abbreviated terms, such as OD, OS, SPH and CYL?

This article will help you decipher all parts of your prescription and discuss it knowledgeably with an optician when you're buying eyeglasses.

What OD And OS Mean

The first step to understanding your eyeglass prescription is knowing what "OD" and OS" mean. They are abbreviations for oculus dexter and oculus sinister, which are Latin terms for right eye and left eye.

Your eyeglass prescription also may have a column labeled "OU." This is the abbreviation for the Latin term oculus uterque, which means "both eyes."

Though the use of these abbreviated Latin terms is traditional for prescriptions written for eyeglasses, contact lenses and eye medicines, some doctors and clinics have opted to modernize their prescriptions and use RE (right eye) and LE (left eye) instead of OD and OS.

On your eyeglasses prescription, the information for your right eye (OD) comes before the information for your left eye (OS). Eye doctors write prescriptions this way because when they face you, they see your right eye on their left (first) and your left eye on their right (second).

Other Terms On Your Eyeglass Prescription

Your eyeglass prescription contains other terms and abbreviations as well. These include:

Sphere (SPH). This indicates the amount of lens power, measured in diopters (D), prescribed to correct nearsightedness or farsightedness. If the number appearing under this heading has a minus sign (–), you are nearsighted; if the number has a plus sign (+) or is not preceded by a plus sign or a minus sign, 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). This indicates the amount of lens power for astigmatism. If nothing appears in this column, either you have no astigmatism, or your astigmatism is so slight that it is not really necessary to correct it with your eyeglass lenses.

The term "cylinder" means that this lens power added to correct astigmatism is not spherical, but instead is shaped so one meridian has no added curvature, and the meridian perpendicular to this "no added power" meridian contains the maximum power and lens curvature to correct astigmatism.

The number in the cylinder column may be preceded with a minus sign (for the correction of nearsighted astigmatism) or a plus sign (for farsighted astigmatism). Cylinder power always follows sphere power in an eyeglass prescription.

Meridians of the eye are determined by superimposing a protractor scale on the eye's front surface. The 90-degree meridian is the vertical meridian of the eye, and the 180-degree meridian is the horizontal meridian. [Enlarge]

Axis. This describes the lens meridian that contains no cylinder power to correct astigmatism. The axis is defined with 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 an eyeglass prescription includes cylinder power, it also must include an axis value, which follows the cyl power and is preceded by an "x" when written freehand.

The axis is the lens meridian that is 90 degrees away from the meridian that contains the cylinder power.

Add. This is the added magnifying power applied to the bottom part of multifocal lenses to correct presbyopia. The number appearing in this section of the prescription is always a "plus" power, even if it is not preceded by a plus sign. Generally, it will range from +0.75 to +3.00 D and will be the same power for both eyes.

Prism. This is the amount of prismatic power, measured in prism diopters ("p.d." or a superscript triangle when written freehand), prescribed to compensate for eye alignment problems. Only a small percentage of eyeglass prescriptions include prism.

When present, the amount of prism is indicated in either metric or fractional English units (0.5 or ½, for example), and the direction of the prism is indicated by noting the relative position of its "base" or thickest edge. Four abbreviations are used for prism direction: BU = base up; BD = base down; BI = base in (toward the wearer's nose); BO = base out (toward the wearer's ear).

Sphere power, cylinder power and add power always appear in diopters. They are in decimal form and generally are written in quarter-diopter (0.25 D) increments. Axis values are whole numbers from 1 to 180 and signify only a meridional location, not a power. When prism diopters are indicated in decimal form, typically only one digit appears after the period (e.g., 0.5).

Additional Information. Your eye doctor also might write specific lens recommendations on your eyeglass prescription — such as anti-reflective coating, photochromic lenses and/or progressive lenses — to give you the most comfortable vision correction possible.

An Example Of An Eyeglass Prescription

Confused? Let's use an example to clear things up. (Pun intended.)

Here is a sample eyeglass prescription:

OD	-2.00 SPH	+2.00 add	0.5 p.d. BD
OS	-1.00 -0.50 x 180	+2.00 add	0.5 p.d. BU

In this case, the eye doctor has prescribed -2.00 D sphere for the correction of myopia in the right eye (OD). There is no astigmatism correction for this eye, so no cylinder power or axis is noted. This doctor has elected to add "SPH," to confirm the right eye is being prescribed only spherical power. (Some doctors will add "DS" for "diopters sphere;" others will leave this area blank.)

The left eye (OS) is being prescribed -1.00 D sphere for myopia plus -0.50 D cylinder for the correction of astigmatism. The cyl power has its axis at the 180 meridian, meaning the horizontal (180-degree) meridian of the eye has no added power for astigmatism and the vertical (90-degree) meridian gets the added -0.50 D.

Both eyes are being prescribed an "add power" of +2.00 D for the correction of presbyopia, and this eyeglass prescription includes a prismatic correction of 0.5 prism diopter in each eye. In the right eye, the prism is base down (BD); in the left eye, it's base up (BU).

An Eyeglass Prescription Is Not A Contact Lens Prescription

Eyeglass and contact lens prescriptions aren't the same. An eyeglass prescription is for the purchase of eyeglasses only. It does not contain certain information that is crucial to a contact lens prescription and that can be obtained only during a contact lens consultation and fitting.

In addition to the information in an eyeglass prescription, a contact lens prescription must specify the base (central) curve of the back surface of the contact lens, the lens diameter, and the specific manufacturer and brand name of the lens.

Also, the power of an eyeglass prescription frequently is modified when determining the best contact lens power. One reason is that eyeglass lenses are worn some distance (usually about 12 millimeters) from the surface of the eye, whereas contact lenses rest directly on the eye's cornea.

An accurate contact lens prescription can be written only after a contact lens fitting has been performed and the prescribing doctor has evaluated your eyes' response to the lenses and to contact lens wear in general.

Your Eyeglass Prescription: It's Yours To Keep

The Federal Trade Commission is the U.S. government's consumer protection agency, and in 1980 the FTC's Prescription Release Rule became law. The rule requires eye doctors (both optometrists and ophthalmologists) to give patients a copy of their eyeglass prescription at the end of an eye exam that includes a refraction.

The rule is intended to protect the "portability" of your eyeglass prescription, allowing you to use it to buy glasses from the vendor of your choice.

Your eye doctor must give you a copy of the prescription whether or not you ask for it. Eye doctors may not condition the release of your prescription on your agreement to purchase eyeglasses from them, nor may they charge you an extra fee to release your prescription. They also may not disclaim liability for the accuracy of the prescription if you purchase eyeglasses elsewhere.

The FTC enforces the Prescription Release Rule, and eye doctors who violate the rule are subject to a civil penalty of $10,000.

If you feel your eye doctor has violated the rule or you want free information on other consumer issues, you can contact the FTC at 1-877-FTC-HELP (1-877-382-4357). 

http://www.allaboutvision.com/eyeglasses/eyeglass-prescription.htm