What You Need to Know About Your Eyeglass Prescription

Those who suffer from nearsightedness, farsightedness, and astigmatism usually wear eyeglasses and contact lenses to improve their vision. While reading glasses are available in drugstores, it’s still better to visit a specialist for an eye exam. Keep in mind that routine eye exams help in the early detection of vision-loss causing diseases like glaucoma.

If you’re given an eyeglass prescription, you’re probably wondering what the numbers and abbreviated terms mean. In this blog post, we’ll discuss everything you need to know about your eyeglass prescription.

What are OD and OS?

Oculus dexter (OD) and oculus sinister (OS) pertains to your left eye and right eye. You may also notice a column labeled “OU” in your eyeglass prescription. OU is an abbreviation for oculus uterque, a Latin term for “both eyes.” Using these abbreviated Latin terms is typical on prescription for eyeglasses, contact lenses, and eye medicine, but some specialists and clinics choose to use modern terms on eyeglass prescription, such as RE or right eye and LE or left eye.

You’ll see that in your eyeglass prescription, the information for your right eye (OD) comes first before the one for your left eye (OS). Eye doctors write prescriptions like that because when they face you during an eye examination, they view your right eye on their left and your left eye on their right.

Other Components of Eyeglass Prescriptions

Sphere (SPH) –  Measured in diopters (D), sphere refers to the amount of lens power prescribed to correct nearsightedness or farsightedness. If you see that the number under this heading has a minus sign (-), it means that you are nearsighted. On the other hand, if it has a plus sign (%20), it means that you are farsighted. The term sphere denotes that the correction for nearsightedness or farsightedness is “spherical” or equal in all of the eye’s meridians.

Cylinder (CYL) – Cylinder indicates the amount of lens power for astigmatism. You have a very slight or no astigmatism that needs correction if this column is blank. This term signifies that the lens power added to correct astigmatism is not spherical. Instead, it’s shaped so one of the eye’s meridians has no added curvature and the meridian vertical to the “no added power” meridian has the maximum power and lens curvature for astigmatism correction. Moreover, meridians of the eye are determined by overlying a protractor scale on the front surface of the eye. The 90-degree meridian is the eye’s vertical meridian while the 180-degree meridian is the horizontal meridian.

Axis – It represents the lens meridian that has no cylinder power to correct astigmatism. The axis is measured from 1 to 180. An eyeglass prescription that includes cylinder power should also include an axis value, following the cyl power and preceded by an “x” when written freehand. The axis refers to the lens meridian that is 90 degrees far from the meridian that has the cylinder power for astigmatism correction.

Add – This term indicates the magnifying power applied to the bottom of multifocal lenses for presbyopia correction. You’ll see that the figures in this part of your prescription are always a plus power though it’s not followed by a plus sign. It usually ranges from %200.75 to %203.00 D and is the same for both eyes.

Prism – The amount of prismatic power is measured in prism diopters, indicated as p.d. or a superscript triangle when written freehand. Eye doctors prescribe it for eye alignment issues and only a small number of eyeglass prescriptions have prism. Its amount is written in either metrical or fractional English units while the prism’s direction is indicated by noting the relative position of its base or thickest edge. Specialists use four abbreviations for prism, including BU or base up, BD or base down, BI or base in (toward your nose), and BO or base out (toward your ear).

Examples of Eyeglass Prescriptions

-3.00 %20 1.50 x 180

%203.5 %20 2.00 x 45

In the first prescription, the patient has 3 diopters of nearsightedness with 1.5 diopters of astigmatism and 180 degrees axis. Meanwhile, the second prescription indicates that the patient has 3.5 diopters of farsightedness, 2 diopters of astigmatism, and an axis of 45.

Eyeglass Prescription VS Contact Lens Prescription

Keep in mind that a contact lens prescription is different from an eyeglass prescription. You can only use an eyeglass prescription for buying eyeglasses. It doesn’t have the necessary information for contact lens prescription, which you can acquire through consulting your Minneapolis optician. While eyeglass lenses are at a certain distance from the eyes, contact lenses are placed directly on the eye. Distance affects the lens power needed for your eyes to focus properly.

A contact lens prescription must indicate the base or central curve of the back surface of the lens, lens diameter, and specific manufacturer or brand name of the lens. The power of an eyeglass prescription is usually altered when finding out the best contact lens power. It’s because you wear eyeglass lenses away from the surface of the eyes while contacts lay directly on the cornea. You can only obtain a proper contact lens prescription after a fitting and your eye doctor has assessed how your eyes respond to the lenses.

Concave Lenses – These lenses are thinnest in the center and the numerical prescription for them always comes with a minus symbol. Concave lenses are for correcting myopia or nearsightedness.

Convex Lenses – Convex lenses are similar to a magnifying glass, they are thickest in the center. People with hyperopia or farsightedness wear these lenses. The numerical prescription for convex lenses always has a plus symbol.

Cylindrical Lenses – Cylindrical lenses curve more in one direction than the other. They are usually used for astigmatism correction.

Frequently Asked Questions About Eyeglasses

Do Reading Glasses Help With Astigmatism?
Reading glasses won’t do much for your vision if you have astigmatism, a different prescription in each eye, or eyes that are closer together or farther apart than usual. You can experience eye strain and headache by wearing one-size-fits-all reading glasses.

How Do You Eliminate Reflections on Eyeglasses?
Anti-reflective coating or AR coating allows others to see your eyes better and get rids of white glare spots in flash photography. If you wish to avoid annoying reflections on your glasses, then this lens coating is for you.

What Are Photochromic Lenses?
Photochromic lenses automatically turn dark when exposed to UV rays. These lenses become clear again once UV is no longer present. They are a great option for people who regularly wear glasses, are always outside, and don’t want to spend more on purchasing a separate pair of prescription sunglasses. However, you should know that photochromic lenses don’t darken as much inside the car. It’s because the glass used in modern vehicles blocks the majority of the sun’s UV rays. Prescription sunglasses are a better option for driving in sunny conditions.

How Can I Extend the Life of My Eyeglasses?
Go for classic-style frames if you’re purchasing just one pair of eyeglasses instead of trendy frames that can quickly go out of style. Choose a style with spring hinges, which lets the temples to flex a little outward without damaging the glasses. Ask to have a scratch-resistant coating applied to your lenses. Further, always follow your eye doctor’s advice for proper eyeglass care.

How Often Should I Get a New Pair of Glasses?
Your doctor will notify you whether your prescription has changed and you require a new pair. To maintain your vision, see your eye doctor at least once a year or they can tell you the best schedule for you.