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How to read your eyeglass prescription

May 03, 2019

Guide to prescriptions

prescription glasses

Our goal is to help you understand what the numbers mean when you put your prescription in manually. At TimetoShade.com we allow you to put in your eyeglass prescription manually or upload your actual prescription which takes the hassle out of not understanding what the prescription numbers mean. Most online retailers will ask you to put in your prescriptions manually. Here is an explanation of the process if you do it this way.

prescription eyeglass

PD Measurement

How to read your eyeglass prescription

So, you've just had an eye exam and your eye doctor has given you an eyeglass prescription. He or she probably mentioned that you

are nearsighted or farsighted, or perhaps you have astigmatism.

(If that's not the case, and you need an eye exam, find an eye doctor 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 read and understand your eyeglass prescription so you can discuss it with an optician when you buy new eyeglasses.

NEED AN EYE EXAM? Find an eye doctor near you, and use your FSA funds to cover the cost of your eye exam or eyewear.

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 common on eyeglass prescriptions for glasses, contact lenses and eye medicines, some doctors and clinics have opted to modernize their eyeglass prescriptions and use RE (right eye) and LE (left eye) instead of OD and OS.

On your eyeglass prescription, the information for your right eye (OD) comes before the information for your left eye (OS). Eye doctors write eyeglass 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 parts of 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 it has a plus 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, you have little or no astigmatism that requires correction.

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 correction of nearsighted astigmatism) or a plus sign (for farsighted astigmatism). Cylinder power always follows the 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.

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 for astigmatism correction.

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 eyeglass 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" (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.

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An example of an eyeglass prescription

Confused? Let's use an example to clear things up. (Yes, 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 and -0.50 D cylinder for the correction of astigmatism. The cyl power has its axis at the 180 meridians, 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.

This eyeglass prescription also includes 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 cannot be used to buy contact lenses

Eyeglass and contact lens eyeglass 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 eyeglass prescription and that can be obtained only during a contact lens consultation and fitting.

Eyeglass lenses are positioned at a distance from the eyes, while contacts rest directly on the eyes. That distance affects the lens power required for eyes to focus properly.

In addition to the information in an eyeglass prescription, a contact lens eyeglass 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. This is because eyeglass lenses are worn some distance (usually about 12 millimeters) from the surface of the eye, whereas contact lenses rest directly on the corner of the eye.

An accurate contact lens eyeglass 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 (FTC) is the U.S. government's consumer

protection agency. In 1980, the FTC's Eyeglass Prescription Release Rule became law. This rule requires eye doctors to give patients a copy of their eyeglass prescription at the end of an eye exam that includes a

refraction The Eyeglass Prescription Release Rule is intended to allow the "portability" of your eyeglass prescription so you can buy glasses from the vendor of your choice.

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

They also may not disclaim liability for the accuracy of the eyeglass prescription if you purchase eyeglasses elsewhere.

Eye doctors who violate the provisions of the Eyeglass Prescription Release Rule are subject to a civil penalty of $10,000 per violation.

How (And Where) To Buy Eyeglass Prescription Glasses Online

Ever heard of a brand called Warby Parker? Us too. They broke the eyeglass industry a few years back by offering eyewear at unprecedentedly low prices, online only. Since then, several other companies have followed in their footsteps.

To help you navigate what the online eyewear market looks like now, we've rounded up just how and where to buy eyeglass prescription glasses online.

Get Your Eyeglass prescription

Sorry for this step you'll have to interact face to face with other humans. Visit a local optometrist and go through the process of updating your eye eyeglass prescription. Make sure you find out your pupillary distance (PD), the horizontal distance across your face between your two pupils.

It's possible to figure out your PD yourself using online resources, but it's always easier to just hand that task over to the experts. Where To Find Glasses Online

You can browse an infinite variety of eyeglasses on an infinite number of websites these days —there's no lack of options in this arena. And while it's convenient to have the product delivered directly to your doorstep, picking out the perfect pair can be daunting.

Many eyewear sites will guide you through this process, offering tutorials on exactly how to pick out the perfect frames for you, including what frames fit your face shape best, and how to utilize your insurance and send in your eyeglass prescription.

After all, these frames are an important purchase — they'll soon become a part of your daily life. But overall, don't sweat it: Brands are constantly getting smarter and offering more educational tools to help you make the right decision.

Check The Return Policy

This may seem like a no brainer, but sometimes it's easy to forget. Checking the return policy is crucial because a piece of eyewear is such a personal purchase. They're on your face, they're how you see the world. Luckily, most sites are sympathetic to this and have generous return policies.

There are so many reasons to love Warby Parker. For starters, its site offers educational tools on how to choose the right lenses for you, which include a short quiz on how to pick your frames and take your insurance, personal budget, PD and eyeglass prescription into account.

Warby Parker's home try-on kit allows you to pick five frames to try for five days, then return the ones you don't want with the already provided prepaid label. The company also offers the Buy A Pair, Give A Pair program, through which it donates a pair of glasses to someone in need for every pair sold.

Overnight Glasses

If you need glasses fast and hassle-free, Overnight Glasses is where you turn. The company ships your glasses in as fast as 24 hours and offers a 100 percent satisfaction guarantee with no questions asked return policy. A plethora of tools and customer reviews on the Overnight Glasses site can help you make an informed decision.

Eyeconic carries a vast array of designer frames for you to choose from. Through its site, you can connect to a doctor to obtain an eyeglass prescription and have your PD measured, and it's the only place that allows you to purchase frames straight through your vision insurance.

Time to Shade does all of its designing in-house to create affordable eyewear. Its site offers education on how to purchase eyewear and read an eyeglass prescription and has a variety of programs, from referrals and loyalty to affiliates and student discounts. Time to Shade also partners with two charities, Feed the Children and The Lions Club, for eyewear donations.


Ready to buy eyeglasses!

"Here at Timetoshade.com, we want to make your experience simple and easy. By understanding your prescription, it will make input of your eye data a breeze."

- Yishai Grossman -

Now you are ready to understand your prescription. You can discuss these with your optometrist as well. These are the most important things to understand when purchasing your glasses online. Now that you finished learning what everything means, what are you waiting for? Begin saving on your next pair of glasses and start shopping here at timetoshade.com right away.

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