Your glasses prescription is a document your eye care provider is required to give you after an exam, and you can request a copy at any time. If you’ve lost yours, there are several straightforward ways to retrieve it. If you already have it in hand but can’t make sense of the numbers, the format is standardized and easy to decode once you know what the abbreviations mean.
Request a Copy From Your Eye Doctor
The simplest route is calling the office where you had your last eye exam. Your prescription is part of your patient record, and the practice is required to provide it to you. In the United States, the FTC’s Eyeglass Rule mandates that eye care providers release your prescription to you automatically after an exam, whether or not you ask for it, and regardless of whether you plan to buy glasses from them. You don’t need to pay an extra fee for the prescription itself.
If you’ve switched providers, you can give your new practitioner consent to request your clinical records from the old one. If the original practice has closed, local optical offices may know where the patient records were transferred, since a closing practice is expected to pass records along to another registered provider.
Check Past Retailers or Insurance Portals
If you ordered glasses online or through a retail chain, your prescription is almost certainly stored in your account. Log in to whatever retailer you last used and look under order history or your saved prescription. Vision insurance portals sometimes keep a copy on file as well, since one was submitted with your claim.
Keep in mind that prescriptions expire. Most states set expiration dates between one and two years from the exam date. If yours has lapsed, you’ll need a new exam to get a current one, no matter how you retrieve the old record.
Why Apps That Scan Your Lenses Are Unreliable
Several mobile apps claim to read your current glasses and determine your prescription from the lenses. The accuracy of these tools is poor. A study reviewed by the American Optometric Association found that none of 34 vision-related apps followed evidence-based clinical guidelines, and researchers found little scientific validity in the prescriptions they produced. Over 82% of users showed confusion while trying to follow the app’s instructions, and only 36% felt confident in the result afterward, compared to 96% confidence after an in-person exam.
These apps are not a substitute for getting your actual prescription from your provider.
How to Read the Numbers on Your Prescription
Once you have your prescription, it’s laid out in a standard table format. The left column labels each eye: OD means right eye (from the Latin “oculus dexter”) and OS means left eye (“oculus sinister”). Some offices just write RE and LE instead. Each row contains several values.
SPH (sphere) is the main corrective power of the lens, measured in diopters. A minus sign means you’re nearsighted and need help seeing far away. A plus sign means you’re farsighted. The higher the number, the stronger the correction.
CYL (cylinder) appears if you have astigmatism, meaning your cornea is slightly more oval than round. This number, also in diopters, tells the lens maker how much additional correction is needed to account for that irregular curve.
Axis always accompanies CYL. It’s a number between 0 and 180 that pinpoints the angle of your astigmatism on the cornea, so the correction is oriented in the right direction. If you have no CYL value, you won’t have an axis either.
ADD and Prism: Values You May or May Not Have
ADD stands for “add power” and only appears on prescriptions for multifocal lenses, like bifocals or progressives. It’s the extra focusing strength built into the lower portion of the lens to help with close-up tasks like reading. This value is always positive, typically ranges from +0.75 to +3.00 diopters, and is usually the same for both eyes. If you’re under 40 and don’t have trouble reading up close, your prescription probably won’t include it.
Prism is even less common. It’s prescribed when your eyes don’t align well with each other, causing double vision. The value is measured in prism diopters and includes a direction: BU (base up), BD (base down), BI (base in, toward your nose), or BO (base out, toward your ear). Most people will never see a prism value on their prescription.
Your Glasses Prescription Is Not Your Contact Lens Prescription
One of the most common mistakes people make is using a glasses prescription to order contact lenses, or vice versa. The numbers are different because glasses sit about 12 millimeters in front of your eye, while contacts rest directly on it. That gap changes the effective power of the lens, so a mathematical conversion is applied. Contact lens prescriptions also include measurements specific to the lens fitting, like base curve and diameter, that don’t appear on a glasses prescription at all.
If you need contacts, you’ll need a separate contact lens fitting and prescription from your eye care provider. An eyeglass prescription alone won’t give you the right numbers.