What Does Your Eye Prescription Mean?

February 26, 2021
What Does Your Eye Prescription Mean?

Whether you're new to having your eyes checked or if you've been wearing glasses or contact lenses for years, your eye prescription is used to know exactly what requirements (if any) are needed to correct your vision. Our lead optometrist, Mai Monavar, is here to help you make sense of those numbers in your eye prescription.

First of all, you'll get your eye prescription from your optometrist once you have your eyes tested. It's important to note that your prescription for glasses and contact lenses will differ slightly, so you'll need to request which one you'll need in specific with your optom. If you already have it, you can validate or renew your current glasses or contact lens prescription right from your phone! Download the Eyebou app to give it a try.

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So what do all those numbers mean?

Your glasses prescription is written in a standardised format so that it can be interpreted globally. Let’s look at an example together:

-1.00 / -0.50 x 180


The first number (-1.00) is the amount of long or short-sightedness you have (also referred to as the “sphere” by your optometrist) and oftentimes referred to as your eye "power" or "strength".  If this number is preceded by a minus sign (as it is here), you need glasses to correct your short-sightedness.  Short-sightedness (also known as myopia) occurs when your eye ball length is too long.  The longer your eye ball, the more short-sighted you are, making your vision more blurry when looking far away. If the first number is preceded by a plus sign (+), you need glasses to correct your long-sightedness.  Long-sightedness (also known as hyperopia), occurs when your eye ball length is too small, causing focusing issues which often result in your eyes feeling tired and achy, and sometimes leading to headaches.


The second number (-0.50) is the amount of astigmatism you have (also referred to as the “cylinder” by your optometrist). This number is also preceded by a minus sign or a plus sign, depending on the prescribing style of your optometrist. Astigmatism refers to the fact that our corneal membranes (at the very front of the eye ball) are rarely mathematically perfectly spherical.  Usually, they will be a little bit more flat or a little more curved in an area making our vision less clear.  The majority of people have some astigmatism, however if yours is minimal, your optometrist might simply prescribe “SPH” or “DS” to indicate that you only require spherical power to correct short-sightedness or long-sightedness.


The third number ( x180) is the angle of your astigmatism (also referred to as the “axis” by your optometrist). The axis is always a number between 1 and 180 on your prescription, preceded by an “x”. If you have no astigmatism, this part of your glasses prescription will be left blank.


If you have any other issues regarding your eyes or are overdue for a chekup, you can book to have a virtual consultation with an optometrist in minutes, right from your laptop or smartphone! Tele-optometry for the win!

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What is “near ADD’? 

As we get older, the architecture of our eyes change.  From around the age of 40 years old, the natural lens inside of our eyes lose their flexibility and so we lose our ability to focus well at close range (unless you are naturally short-sighted which counteracts this effect to a certain degree).  This natural change is called presbyopia.  When we become presbyopic, we need additional magnification in our glasses to accommodate for the fact that our eyes can no longer focus well at close range.  This amount of extra magnification is called the reading or near ADD, and will be a different value at different near work distances, e.g. we will typically need more magnification at shorter working distances (looking at your phone), and less magnification at longer working distances (looking at your desktop screen). The near ADD is always preceded by a “+” sign and is usually a number between 0.75 and 3.00.


What is “prism”?

Prism is a modification that your optometrist will apply to your glasses prescription if your eyes are having a hard time aligning with each other.  It can be applied to just one or to both of your glasses lenses.  It will typically be a small number followed by a ∆ symbol and two letters which related to the orientation of the prism e.g. 1 ∆ BO


Will wearing glasses make my eyes lazy or worse?

This is a very common misconception, so let's get some clarity.  The reason we need to wear glasses at all, is because there is a structural irregularity of one or both of our eyes, e.g. our eyes are too long, too short, or our corneas are too curved or too flat.  Wearing our glasses will not shrink or grow our eye balls or change the curvature of our corneas, they simply focus the light onto the right place, the retina, which allows us to see clearly.  

Let's also consider that if our eyes are made to over-work (like in the case of long-sightedness), and we choose not to wear our glasses, we may develop tired, achy eyes and sometimes headaches.  But by wearing our glasses, our eyes do not have to over work or over-focus, the light entering our eyes is focused in the correct spot, and we no longer have tired or achy eyes.

It’s also helpful to remember that our long or short sightedness and astigmatism do not magically disappear throughout the day (although they will always change across our lifetimes).  So if your optometrist has recommended that you wear glasses full time, this will allow you to see to the best of your ability, whilst also stopping your eyes from becoming tired and achy, and usually allowing you to feel more energised and able!

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