The simplest way to find out your eye prescription is to ask your eye doctor’s office. By federal law, they’re required to give you a copy of your prescription after every exam at no extra charge. If you’ve never had an exam, or your prescription has expired, you’ll need a new comprehensive eye exam to get an updated one.
Get a Copy From Your Eye Doctor
The FTC’s Eyeglass Rule requires optometrists and ophthalmologists to provide patients a copy of their prescription after every eye examination, free of charge. They also cannot require you to buy glasses or contacts from them as a condition of the exam. So if you had an eye exam recently but walked out without your prescription, simply call the office and ask for it.
If you’ve switched providers or moved, your old records are still accessible. Under HIPAA, you have the legal right to request copies of your health records from any provider who treated you. In most cases, the office must respond within 30 days. If your records are stored off-site, they get up to 60 days. They can’t charge you for searching or retrieving the information, though they may charge a small fee for copying and mailing.
One important caveat: prescriptions expire. Most states set their own expiration rules, so yours may no longer be valid for purchasing new glasses or contacts. If it’s been more than a year or two since your last exam, you’ll likely need a fresh one regardless of whether you can track down the old paperwork.
What Happens During an Eye Exam
If you need a new prescription, a comprehensive eye exam is the only reliable way to get one. The key part for determining your prescription is called refraction. The doctor places an instrument in front of your eyes and cycles through different lenses while you look at a chart. You’ll be asked which lens makes things clearer (“one or two?”), and your answers help the doctor zero in on the exact correction you need. They’ll also use a lighted instrument to measure how your eyes bend light, which gives them an objective starting point before fine-tuning based on your feedback.
In some cases, the doctor will use eye drops to temporarily prevent your eyes from adjusting their focus during testing. This is common for children and for adults whose eyes may be compensating in ways that mask the true prescription.
Without vision insurance, a routine eye exam in the U.S. averages about $136, with prices ranging from $105 to $257 depending on location and the specific tests performed. With vision insurance, the average drops to around $25.
How to Read Your Prescription
Once you have your prescription, it helps to understand what you’re looking at. The numbers and abbreviations can seem cryptic, but each one describes something straightforward about your vision.
- OD and OS: OD is your right eye, OS is your left eye. Every prescription lists corrections for each eye separately.
- SPH (Sphere): The main lens power needed to correct your vision. A minus sign means you’re nearsighted (trouble seeing far away). A plus sign means you’re farsighted (trouble seeing up close).
- CYL (Cylinder): How much astigmatism you have, if any. Astigmatism means your eye isn’t perfectly round, so light focuses unevenly.
- Axis: A number between 1 and 180 that indicates the angle of your astigmatism. This only appears if you have a CYL value.
- Add: Additional magnifying power for reading, typically found on prescriptions for people over 40 who need bifocals or progressive lenses.
A prescription reading something like OD -2.50 means your right eye needs a moderate correction for nearsightedness. The higher the number (ignoring the sign), the stronger your prescription.
Glasses and Contact Prescriptions Are Not the Same
If you have a glasses prescription and want contacts (or vice versa), you can’t simply use the same numbers. Contacts sit directly on your eye, while glasses rest a few millimeters away on your face. That small gap changes how much the lenses need to bend light, so the power values are often slightly different between the two.
Contact lens prescriptions also include measurements that glasses prescriptions don’t: a base curve (the curvature of the lens to match your eye’s shape) and a diameter. These ensure the contact fits properly. You need a separate fitting for contacts, which is why eye doctors treat them as a distinct prescription.
Measuring Your Pupillary Distance
Your prescription alone isn’t enough to order glasses, especially online. You also need your pupillary distance (PD), the distance in millimeters between the centers of your pupils. This ensures the lenses are centered correctly in the frames. Some doctors include PD on the prescription, but many don’t since it’s technically a fitting measurement rather than a medical one.
You can measure it at home with a millimeter ruler and a friend. Stand at a comfortable distance, have your friend hold the ruler against your brow, and line up the zero mark with the center of one pupil. The millimeter mark that lines up with the center of your other pupil is your PD. Most adults fall somewhere between 54 and 74 mm.
If you don’t have a helper, you can use the felt-tip marker method: put on your current glasses, focus on an object at least 20 feet away, and mark a small dot on each lens directly over the distant object. Then take off the glasses and measure the distance between the two dots with a ruler. Many online retailers also offer digital PD measurement tools through their websites or apps.