How to Understand Your Eyeglass Prescription
and Order the Eyewear You Actually Want

Purchasing eyeglasses might seem simple at first, but when you sit down to decipher your prescription just so you can order a pair you love you may find yourself confused.  Because vision professionals don't always write their eyeglass prescriptions in the same format, and you may or may not have every value filled in, it can be difficult to know if you're getting it right—and one little error can result in a pair that won't help you see.

Fortunately, once you get the  hang of how to read your prescription it's actually pretty easy, and we can help you with that! Let’s go over what you need to know to make sure you get your perfect pair of eyeglasses.

Own Your Prescription

                             You know you need a current prescription, but if you don't have one yet or need an update you can visit your preferred optometrist, find a good one in your area, or even get your prescription online right now.
Either way, make sure you get a copy of your prescription because that information gives you the freedom to order your frames and lenses from anywhere you choose. That freedom can save you a lot of time and money, so keep it somewhere safe and easy to locate or take a picture and save it in your smartphone.

                                                                                                                         It's Your Legal Right!
Your eyewear prescription is not only helpful to have, but your legal right. The Federal Trade Commission issued a Prescription Release Rule in 1978 so that both optometrists and ophthalmologists must provide their patients with their prescription after an eye exam warranting one.

                                                                                             "The Prescription Release Rule, promulgated in 1978, requires that
                                                                                                                        optometrists and ophthalmologists provide their patients with a copy of the patients'
                                                                                                                        eyeglass prescription immediately after an eye exam is completed and at no extra cost.
                                                                                                                        The rule also prohibits optometrists and ophthalmologists from conditioning the availability
                                                                                                                         of an eye exam on a requirement that patients agree to buy their ophthalmic goods from
                                                                                                                         the optometrist or ophthalmologist. The rule further prohibits optometrists or
                                                                                                                        ophthalmologists from placing on prescriptions or giving to patients, certain disclaimers or
                                                                                                                        waivers of liability."
                                                                                           United States Federal Trade Commission (FTC)

                                               Unless your doctor determines you do not need corrective lenses, she or he must release that prescription—so make sure you get it!

                            What You Need to Know

Understand Your Lens Measurements

To order frames, you don’t even need the actual prescription paper but rather a series of measurements specific to you that ensure you get the lenses your eyes require. Let’s go over each measurement so you know what they are, what they mean, and how to provide them when ordering eyeglasses.

Pupillary Distance and Prism

First, you need to know you Pupillary Distance (PD). It’s a vital measurement and yet is often left off of prescriptions, but you can measure it by yourself or with the help of a friend. If you’ve got your measurements on your prescription already, let’s make sure it’s the right number.

Some prescriptions will have numbers for Distance PD, Near PD, or both. The distance value indicates the primary measurement and will come first. The near value indicates a separate measurement for reading glasses, so unless that’s the type of eyewear you’re ordering you can ignore your Near PD number entirely.

One more thing: you may also have a Prism value on your prescription, measured in prism diopters.  Just like Pupillary Distance, prism diopters may be abbreviated as PD.  Generally speaking, your prescription will say Prism or use a triangle for shorthand to avoid confusion.  If you have a PD value between 0 and 1, however, that's likely a prism diopter value.  Higher values are measurements in millimeters and denote your Pupillary Distance.

Sphere, Cylinder, and ADD

Second, you need the Sphere (SPH) measurement for both your left and right eyes. SPH indicates the amount of lens power, measured in diopters. These values are used to correct issues near- and farsightedness. Negative numbers mean you’re nearsighted and positive numbers mean you’re farsighted.

You also need the Cylinder (CYL) value for both your left and right eyes as well. CYL determines the lens power necessary to correct astigmatism. You may have no CYL value which means you have no astigmatism, or it’s so negligible you do not require any corrective measures. Just like your SPH value, negative and positive values correlate with near- and farsightedness (respectively).

Your ADD value, if you have one, simply denotes additional magnifying power to correct presbyopia. If you have one, make note of it. If you don't, it doesn't matter.


Third, and finally, you may need to know your Axis and ADD measurements.  It's entirely possible you won't have either of these values defined, but if you do they are important.

Let's start with Axis.  If you have a cylinder value on your prescription, you will also have an Axis.  It denotes the vertical meridian of the eye, and that tells opticians the precise direction needed to position the cylindrical power of your lenses.  Confused?  This measurement basically makes sure the power necessary to correct your astigmatism is exactly where it needs to be so your eyeglasses do their job.

Think about it this way: a blindfold will successfully block a person's vision when tied around the eyes, but if you didn't know where the eyes were you might tie it around someone's mouth instead.  The blindfold still has the ability to do its job, but because you didn't know where to put it that never actually happened

Know Your Frame Measurements, Too

Lens measurements can feel a little overwhelming, but that's why you go to a professional and get a prescription. If you feel like you need a break from understanding all the numbers that help you see, you're in luck. Frame measurements require very little effort to find because they're most likely engraved on the inside of your current eyeglasses.

                                                                                                        You'll usually find these numbers on the inner side of the temple, but you may find them on the bridge as well. Before we get into the numbers,
                                                                                                        let's make sure we're familiar with what these measurements refer to in the first place.

                                                                                                       Bridge size refers to the area meant to rest over your nose, eye size refers to the length of the area covering a single eye,
                                                                                                       and temple length simply states the length of the long bars that rest over your ears so your glasses don't fall off of your face

Finding the measurements on a pair of existing frames may not prove difficult, but how do you understand what the numbers mean? The range each measurement can take is unique, so if that number falls in between one of the specific ranges you'll know right away.

Your frames may also denote two additional measurements: lens height and frame size.  Eye size is essentially the same as lens width, so your lens height is just another measurement to help determine your ideal frame size.  Frame size, or the total frame width, specifies the length of the frames from one end to the other as they rest across your face.  This measurement is rather important, as it can help you pick a comfortable pair of frames even if you're lacking other measurements.  Frame size is, approximately, just two times your eye size/lens width plus your bridge size.

Unlike the lens values on your prescription, frame measurements do not require absolute precision.  Most people will find that frames remain comfortable despite slight variances in these numbers.  Don't panic if you make an error of 1-2mm.  It's best to get it right, but if the difference is that small you probably won't even notice.

                                                                                      Consider the Shape of Your Face
Before you're all set to get a great new pair of frames, you ought to consider the shape of your face.  Certain styles flatter different face shapes better than others, and sometimes it's a case of opposites attracting.  For example, round faces work well with rectangular frames and square faces look great with round frames.  Other times it's not so simple.  Either way, our face shape chart will help you locate the most flattering option for you.


Now you know how to order the eyeglasses you want with confidence.

Understanding your lens and frame measurements gives you the ability to shop freely and choose the eyeglasses you love at a price you can afford.  If you're seeking a range of fun, elegant, and captivating styles at surprisingly low cost, be sure to consider Eyewear Insight when shopping for your next great frames.

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