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Terminologies: Understanding Your Eyeglass Prescription

When you place an order for your new prescription eyeglasses, all you need to do is hand in your prescription to your local optometry clinic or optical shop. However, it wouldn’t hurt to learn more about the terms your optometrist scribbled on the prescription pad.

Eyeglasses prescription

Here’s what the terms on your prescription mean:

O.D., O.S. and O.U.

In the first column, you’ll find the terms O.D. and O.S., which stand for oculus sinister (left eye) and oculus dextrus (right eye), respectively. If the prescription refers to both eyes, your optometrist will write O.U., or oculus uterque.

Sphere (SPH)

The numbers under this column indicate the strength of your prescription and, by extension, how bad your eyesight is. A + sign before these numbers indicates your farsighted, while a - sign means you are nearsighted.

Cylinder (CY)

If you have astigmatism, your optometrist will indicate the lens power needed to correct the curvature in your eyes. Astigmatism is a condition caused by an irregularly shaped cornea. The curve of your cornea (the front of your eye’s surface) is supposed to resemble a round ball, but in people with astigmatism, the cornea is egg-shaped. This irregular curve blurs vision at certain distances. Like the numbers in the sphere column, a - sign indicates nearsighted astigmatism, while a + sign indicates farsighted astigmatism.

What if you don’t have astigmatism? The eye doctor from your local optometry clinic will leave this column blank.


The number in this column indicates the extent of your astigmatism or your cornea’s curvature.

Pupillary Distance (PD)

Your eyeglass prescription might also include the pupillary distance (PD) for your eyeglasses. The PD refers to the distance between the center of one pupil (the black center of the eye) to the center of the other pupil and will tell you where the optical center of your new lenses should be located.

Additional Information in the Prescription

The aforementioned terms should be found in every prescription. However, your eye doctor might include some additional information in your prescription such as:

  • Lens design - Your optometrist may have indicated on your prescription the design for and function of your new lenses. For instance, your optometrist might have written down that your new glasses should have bifocal lenses, which have two lens powers.

  • Lens brand - Occasionally, your optometrist might recommend a specific brand of lens.

  • Vision enhancement features - Your new prescription eyeglasses should be able to correct your vision, but certain features may be needed to enhance your vision’s clarity. Here are some popular features your optometrist might recommend or you might want to try:

    • Anti-reflective coating - Lenses with anti-reflective coating can reduce glare and help you see better during the daytime.

    • Ultraviolet (UV) protection - UV rays can damage your eyesight over time. That’s why eye doctors recommend patients who spend a lot of time outdoors wear prescription glasses with UV-resistant coatings to reduce the risk of UV-related damage.

    • Transition lenses or photochromic lenses - Alternatively, you can wear sunglasses while spending time outdoors. If you don’t want to go through the trouble of having to carry two pairs of glasses every time you go outside, you might want to consider getting prescription eyeglasses with transition or photochromic lenses. These have a tint that darkens in the presence of bright light and lightens in darker settings.

    • Blue-light-blocking lenses - Digital devices emit blue light, which can cause eye strain over time. That’s why your optometrist may prescribe these lenses if you tend to spend a lot of time in front of a computer screen.

Important note: It’s important that you inform your optometrist about any preferences you might have during your routine eye exam. That way, they can take into account your lifestyle when they make recommendations in your prescription.

Difference Between Eyeglass and Contact Lens Prescriptions

This might seem like a no-brainer, but it’s important to remember that you can’t use eyeglass prescriptions to purchase contact lenses—you’ll need to undergo another eye exam and ask for a different prescription for contact lenses. Prescriptions for eyeglasses and contact lenses use similar terms, but contact lense prescriptions contain additional information such as:

  • The base curve (BC) for the lenses - This indicates the size of your contact lenses.

  • The diameter (DIA) of the lenses - The DIA indicates the length of your contact lenses. If your contact lenses don’t have the correct length, they won’t be able to cover the cornea properly.

  • Expiration date - In general, you’ll need to replace your lenses every year, although this depends on the type of lenses you’re using. For instance, disposable lenses should be thrown away after use at the end of the day.

Keep in mind that lens prescriptions also have an expiry date. They usually last one to two years, but as a rule of thumb, you should see your optometrist for a comprehensive eye exam every year.

Do You Need Prescriptions Even For Costume Contacts?

What about cosmetic eye lenses? Do you need a prescription for them? Yes; all contact lenses are classified as a medical device, and as such are regulated by the FDA. Costume contacts are no exception. That’s why you should only purchase contact lenses from licensed optical shops or eye care clinics.

Choosing New Eyeglass Frames

If the frames for your eyeglasses are starting to look a bit bent or worn, you may want to replace them the next time you make an order for your new prescription lenses. Consider your face shape, eye color and personal style when looking for a new pair of eyeglass frames. For many patients, choosing a new pair of eyeglass frames is mostly a matter of aesthetic preference. However, you should consider the durability of your new frames as well.

To help you choose the right eyeglass frames, here’s an overview of the most widely used frame materials:


  • Memory metal - Memory metal, which is made of 50% titanium and 50% nickel, is extremely flexible, making it a smart choice for children’s eyeglasses. Even after being bent or twisted, frames made from memory metal will return to their original shape.

  • Titanium - Thanks to their durability, hypoallergenic titanium frames are quite popular.

  • Beta titanium - Beta titanium frames, which are made from titanium mixed with amounts of aluminum and vanadium, are more flexible than pure titanium frames, so they’re easier to adjust.

  • Beryllium - Beryllium is a cost-effective alternative to titanium. Like titanium, beryllium is corrosion resistant. It’s also tarnish-resistant, making it a suitable choice for patients with high skin acidity.

  • Stainless steel - Eyeglass frames made from this iron-carbon alloy are lightweight, durable, flexible, corrosion-resistant and usually come in matte or polished finishes.

  • Aluminum - Lightweight, corrosion-resistant aluminum is frequently used in high-end eyewear.


  • Zylonate (Zyl) - Zylonate is a cost-effective material that also happens to be the most popular material used in plastic eyeglass frames. Zyl frames come in a wide variety of colors, giving you maximum flexibility when it comes to choosing a design for your new frames.

  • Propionate - Thanks to its exceptional durability and flexibility, propionate is often used in sports eyewear. Eyeglass frames made from this nylon-based plastic are durable, flexible, lightweight and hypoallergenic.

One more thing: if at any point you start having trouble seeing clearly even with your eyeglasses on, don’t hesitate to see your optometrist for a comprehensive eye exam. The prescription for your eyeglasses might need to be adjusted.

Looking for optometrists near your area? Scope Optometry offers a wide range of professional eye care services, including eye exam and optometry services. To schedule an appointment, call us at (949) 979-4311 or (949) 409-3040. You can also fill out this form to get in touch with us. Talk to us today!

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