Over 150 million people in the United States wear corrective eyewear, designed to compensate for issues such as nearsightedness and farsightedness. If youre one of them, you know how expensive and time consuming it can be to get a prescription and new frames. Keep in mind that eyeglass prescriptions usually last from 1 to 2 years. If its been that long since you got your prescription, it may be better to see an eye doctor for a health checkup and to get your most up-to-date prescription and best fit.If you have existing eyeglasses and youre confident the prescription is up-to-date, you can try a service such as the GlassesUSA Prescription Scanner app to get your prescription details.Keep in mind that the accuracy of apps like this to measure eyeglasses is unknown and, depending on your prescription, this is not the best way to measure the prescription of your eyeglasses.In this article well go over the steps I took when trying to use the GlassesUSA Prescription Scanner app, as well as other options you have for figuring out the prescription of your glasses.How we tested the GlassesUSA Prescription Scanner app I tried out the scanner app using:my own eyeglasses, which are outside the apps range: trifocal lenses with a complex prescription for presbyopiaa second pair of eyeglasses, with single vision lenses for nearsightedness in a simple prescriptionIm a computer literate, older woman with a complicated prescription. I currently wear trifocal eyeglasses, which include a prescription designed to address presbyopia, an age-related eye condition.Scanning lenses that GlassesUSA doesnt makeI knew that GlassesUSA wasnt designed for my type of prescription, but out of curiosity I completed the scan using my own eyewear. How the first scan wentAfter doing all of the steps, a screen came up indicating that my glasses were out of range and couldnt be read. Even though this confirmed that I couldnt use the app, it was good news because it showed that the GlassesUSA app read my prescription correctly, and gave me accurate information that it couldnt be filled.How the second scan wentI tried it a second time with my own eyewear, so that I could get a better handle on all of the screens. I was surprised that this second try brought a different result. The app took me through the entire process and continued to try to read my prescription at 99 percent complete for over 20 minutes. It never finished and never sent me an error message. Scanning lenses that GlassesUSA can makeNext, I borrowed a pair of eyeglasses from my son, whos nearsighted and has a simple prescription that fits within the GlassesUSA range. This range is for single vision prescriptions between -6.00 to +3.00 and cylinder up to -2.50.Next, I go over the steps I took with his glasses, using the GlassesUSA app.You can read more about the Prescription Scanner app on GlassesUSA.com.Downloading the GlassesUSA appFrom its website. Open up the GlassesUSA website on your computer. Towards the bottom of the homepage theres a download app prompt where you can request the app link.From the app store. You can also download the GlassesUSA app directly through the app store on your phone. Its available for both iOS and Android.Scanning from the appOnce the app is opened, click Start scan. The app uses voice prompts to get you from one step to the next, which is very helpful. What youll needThe screen will show the tools you need to complete the scan. These are:computer with a screen that measures 12 x 27standard magnetic card for scalingyour eyeglasses Whats a magnetic card?Cards with magnetic strips are generally the size of a standard credit card. These include gift cards, debit cards, and some ID and transit cards. GlassesUSA describes using a magnetic card to take certain measurements and images for the scanning app.We suggest using something without identifying markings and without account information on it. Tech setup and calibratingYoull receive a web address to log into from your computer, where youll see a QR code to scan. This syncs your phone to your computer.If your computer doesnt have functional cookies enabled, you wont be able to complete this step. While I did have cookies enabled I couldnt complete this step in Google Chrome. I tried Chrome on another computer but got the same result. I had better luck with Microsoft Edge, and was able to scan the QR code through that.Once the code is scanned, youre prompted to scale the exact size of your computer screen, using a magnetic card. This sounds easy, but may take several tries before it calibrates. If it doesnt work instantaneously, youll have to hold the card flat against the screen. I had to adjust the screen up and down many, many times before it calibrated. This took multiple tries on two computers for around 15 minutes.Scan your current pair of eyeglassesOnce things are calibrated, the app is ready to scan your glasses. You do this by holding your glasses midway between your phone and computer. Youll be prompted to tilt your glasses repeatedly until theyre read. This takes around 3 minutes.Take a photo for your PD measurementYoull be asked to take a selfie with the magnetic card held between your eyebrows. This is done to measure your pupillary distance (PD). This vital step ensures that the lens power of your eyewear is correctly centered.GlassesUSA will then request your account information, and will provide you with your prescription, so that you can purchase glasses.If you have a prescription on hand to compare your GlassesUSA prescription to, you can be better assured of its accuracy. If information privacy is a concern to you, use any card that is credit-card sized (such as a library card) or cover information like numbers and names.Just remember that you can request your prescription details from the office where you last had an eye exam. Theyre required to share a copy with you.If youre looking for other options to find out your prescription based on existing glasses, there are other scanning apps like the one GlassesUSA offers.Liingo RX Reader.Liingo Eyewear also has an app that you can use to get the prescription of your current glasses, by downloading the app, calibrating hardware, and scanning your lenses.GlassesOn app.6over6 offers its GlassesOn app to take measurements similar to GlassesUSA Prescription Scanner to get PD and lens details.Lens Scanner App.SmartBuyGlasses, an eyeglass retailer, partnered with 6over6 to offer its own version of an eyeglass scanning app.There are several online retailers, including GlassesUSA, where you can have your current eyewear prescription read. Some retailers also offer vision checks, which are assessed by ophthalmologists. However, according to the American Academy of Ophthalmology (AAO), these arent as accurate as in-person exams and these vision checks dont assess eye health. These services may be less expensive for purchasing eyewear than some brick and mortar retailers.They are typically best for simple prescriptions. If you wear bifocals or have any other type of complex or strong prescription, seeing an eye doctor in person may be your best first step.Once your prescription is in hand, you can use an online retailer, if you choose. What GlassesUSA isnt forThe app doesnt accommodate:strong or weak prescriptionsprism prescriptions used to correct double visionmultiple prescriptions within one lens, such as bifocals or multifocalscontact lens prescriptions