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5 Things Your Eye Prescription is Telling You

After your eye exam at the optometrist, the next step is to get your eye prescription. We all know these are details specific to our vision needs, but how do they actually tell you what kind of glasses to get?

We’re sure you have a lot of questions if this is your first time reading about them:

  • How do I read an eye prescription?
  • What do these numbers have to do with my eyes?
  • What’s OD vs OS?
  • How bad is my eye prescription?
  • What constitutes a legally blind prescription?

As an optometrist with over a decade of experience, explaining the answers to all these is second nature! So I’ve broken down everything you need to know and why it matters for your personal eye health, in a 5-part simple guide.

1. Why Does OD vs OS Matter?

Like most of our body, symmetry is not a given! Dominant parts of our body, like being right or left handed, mean it’s common for one side to be stronger than the other. The same is often true for your eyes. Which is why your eye prescription gives you a full breakdown of both the left and right eye.

“OS” is your left eye. “OD” is your right eye.
Also, an easy way to remember is the right eye (OD) will always be listed above the left eye (OS).

Eye Prescription

2. “SPH” or Sphere Meaning

To correct your eyesight, you need a specific type of lens power. The strength of your prescription increases as the value moves further away from zero. This applies to either the negative or positive side.

You are likely asking yourself, “How bad is my eye prescription?”

  • +/-1.00  is quite modest; your eyesight isn’t too bad!
  • Below a -6.00 or above a +4.00 is a high prescription. 
  • A prescription below -6.00 can result in 20/200 vision uncorrected. 
  • 20/200 vision is considered legally blind in Canada.
    • This means a person cannot be more than 20 feet away to see what someone with normal vision would see at 200 feet.

What About the + and – on my Eye Prescription?

Minus (-) powers means the prescription is nearsighted, making far-away objects look blurry.

Plus (+) powers means the prescription is farsighted, making nearby objects look blurry.

3. Cylinder = Your Astigmatism

Eyes are perfectly round, right? Not always. When they are, light enters the eye and bends evenly to give you a clear image. However, if your eye is more oval-shaped (curvature imperfection), it provides only partial focus on an object and causes objects to look blurry, wavy, or distorted. 

This is called astigmatism and is a common reason patients would need an eye exam with an optometrist. 

In fact, it is one of the most common vision problems that impacts more than 150 million Americans. Eye exams are vital, and the resulting eye prescription indicates the degree to which your eyeglasses or contact lenses need to offset the curvature of your cornea or lens in order to help you see clearly.

The cylinder number indicates how severe your astigmatism is. 

4. Axis 

If you were thinking of a Y and X axis from math, you wouldn’t be far off! Ranging from 1-180 degrees, the axis indicates which way the astigmatism is angled.

Eye Prescription

 5. Prism

Sometimes our eyes don’t move in sync with each other or can be crossed (strabismus), causing symptoms such as double vision. This is a top vision issue children can have.

Why this matters: Ocular motility and binocular vision are important for reading, driving, and tracking moving objects — all of which are required for most jobs, playing sports, and even maintaining pedestrian safety. 

So what does this have to do with prisms? Prisms split light, and so do your eyes. However, if you see this on your eye prescription, it’s because your eyes require a special type of correction to prevent double vision (seeing two separate images of the same object). The prism fuses the two images together, so only one image is seen.

What About the Meaning of Base?

Similar to your axis, the placement of the prism is vital in order to correct the double vision, with your eye prescription notating the direction of the prism’s thickest edge, or base.

Now if you see extra sections on your eye prescription, we’ve also got you covered! 

Eye Prescription

Do I Need Progressive Glasses? The ADD on Eye Prescriptions

Progressive, or reading glasses  are commonly required by people over the age of 40. A progressive lens eliminates the need for multiple sets of eyewear by providing reading vision in the lower part of the lens, distance vision in the top part of the lens and intermediate vision in the middle of the lens. Multifocal contact lenses also provide clear near and distance vision through one set of lenses.

What does PD Mean?

Pupillary Distance (PD) is the distance between your pupils. Your face shape, size, features, and other factors all go into determining your pupillary distance.

Do you have: 

  • A flatter nose bridge?
  • Higher cheekbones?
  • A wider face?
  • Or are of Asian descent?

Then you may experience problems with frames that are too tight around your temples or glasses that constantly slide down the bridge of your nose.

Eye Prescription

And the benefits of all the precise measurements from your eye prescription go out the window! Asian Fit Glasses, also known as low bridge glasses, are specifically designed for this purpose. Discover the 4 best tips for picking glasses for your face shape.

Our Award-Winning Comprehensive Eye Exams

As you can see, prescriptions and the details on them are incredibly specific to not just each person, but each eye. And because our eyes change as we age, are pregnant, experience eye injuries, based on our medical history of diabetes or high blood pressure, and much more, a comprehensive eye exam is more than just a routine test; it is essential to your long-term vision health. 

If you are experiencing red eyes, blurry vision, loss of vision, or it’s just been a while, then now is the time to book your eye exam. 

Real Eyes Optometry is currently accepting new families and patients of all ages, including kids! 

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