A Doctor’s Guide to Understanding Your Eyeglass Prescription

Eyeglasses have been around for centuries. While some wear a pair for fashion, most still need them for their eye health. Eyeglass prescriptions are incredibly common. In fact, in the United States alone, millions of people rely on prescription glasses to perform daily activities! Your prescription determines the exact correction your vision needs. So, how do you understand it?

What Are Eyeglass Prescriptions?

An eyeglass prescription is an eye care professional’s written order specifying the corrective lens power needed to improve your vision. You get one after an optometrist vision test, which assesses how well your eyes focus at various distances.

Your eye doctor will ask you to read a series of letters or numbers projected on a chart to check your visual acuity, check your pupillary reflexes to see how your pupils respond to light, examine fluid pressure, and more. All these tests help them determine the state of your eyes and, subsequently, your eyeglass prescription.

Eyeglass prescriptions are important because they guide opticians in creating customized lenses. When you wear the wrong prescription, you may experience headaches, eye strain, and dizziness, which can all impact your quality of life.

The Components of an Eyeglass Prescription

Eyeglass prescriptions can confuse anyone who is not an eye care expert. However, knowing what these numbers and abbreviations mean can provide valuable insights. Here are some of them.

OD and OS

The first things you will see on your eyeglass prescription are “OD” and “OS,” which stand for oculus dexter (right eye) and oculus sinister (left eye), respectively. Prescriptions may vary between the two eyes even if you always use them at the same time.

Sphere (SPH)

The sphere (SPH) value indicates the degree of nearsightedness or farsightedness. If your SPH has a minus (-) sign, you are nearsighted (myopia), meaning it is difficult to see distant objects clearly. If your SPH has a plus (+) sign, you are farsighted (hyperopia) and struggle with close-up vision. The further the number is from zero, the stronger the correction needed.

Cylinder (CYL)

The cylinder (CYL) measurement corrects astigmatism, a condition where the cornea has an irregular shape. Any number in this field indicates you need help with blurry or distorted vision.

Axis

The axis value specifies the astigmatism correction’s orientation, measured in degrees from 1 to 180. This number represents the angle at which the corrective lens should be positioned to counteract astigmatism properly.

Add

This value is primarily for bifocal or progressive lenses and indicates additional magnifying power. The upper segment of the lens is for distance vision, while the lower part handles reading or close-up work. Eye doctors commonly prescribe it for individuals over 40 experiencing presbyopia, an age-related loss of near vision.

Prism

A prism correction is necessary if you have eye alignment issues like double vision or strabismus. It helps correct how light enters your eyes to improve focus and coordination.

Reading and Understanding Your Eyeglass Prescription

You do not really have to know what the number and letters in your eyeglass prescriptions are telling you. After all, it is the eye doctor’s and optician’s job to fill and interpret your prescription accurately. Still, understanding gives you an idea of what is going on with your eyes and how the eyeglasses help. Moreover, if you keep your prescriptions, you get to monitor the progression of any vision concerns.

To decipher your eyeglass prescriptions easily, take these expert tips:

• Begin With the Key Abbreviations: Start with the letters because they give you a quick rundown of the type of lenses your eye doctor prescribed. OD means right eye, while OS means left eye. SPH is “sphere,” and CYL is “cylinder.”

• Learn About the Numbers: The numbers hint at the lens powers your eyes need to see clearly. The higher your SPH value, the more severe your nearsightedness or farsightedness problems. As for CYL, the numbers are for your astigmatism angle.

• Communicate With Your Optician or Optometrist: Consult your optician or optometrist about your prescription. They can clarify measurements and explain how your glasses will work.
  

Optica Optometry: Ask Your San Francisco Optometrist

At Optica Optometry, we are all about helping people see. If you have any questions about your prescription, our team is ready to answer. We have experts to guide you in choosing the right frames and lenses, keeping you comfortable and confident with your prescription glasses in San Francisco. Schedule an appointment today!