How to Read an Eyewear Prescription

Have you just received your prescription for glasses and feel like you're reading a secret code? Don’t worry, you’re not alone. These lines of numbers and abbreviations can seem intimidating, but they contain valuable information about your vision. At Lapaire, we believe that understanding your eyesight is the first step to taking good care of it. In this simple guide, we’ll break down your glasses prescription together, step by step, so you can become an expert on your own correction.

The Basics: OD, OS, and General Information

Before diving into the numbers, let's start with the basics: identifying which eye we're talking about. On every prescription, you will find two fundamental acronyms:

OD: Right Eye (from the Latin Oculus Dexter)
OS: Left Eye (from the Latin Oculus Sinister)

Sometimes, you might see the letters "R" (Right) and "L" (Left) on international prescriptions. The correction information is always presented separately for each eye, as it's very common to have different needs for the right and left eye.

Your prescription also contains important administrative information like your name, the date of the exam, and the stamp of the ophthalmologist. Always check that this information is correct. The prescription's expiry date is also an element to consider, as your vision can change over time.

The Main Correction (Sphere): Short-sightedness or Long-sightedness?

The most important column is often titled "Sphere" or "SPH". It indicates the basic lens power needed to correct your vision. This is the primary reason for needing glasses. The value is expressed in dioptres, the unit of measurement for a lens's power. The most important thing to remember is the sign that comes before the number.

The Minus Sign (-) for Correcting Short-sightedness

If the number in the "Sphere" column is preceded by a minus sign (for example, -2.50), it means you are short-sighted (myopic). Short-sightedness is a vision problem that makes distant objects blurry, while near vision generally remains clear. The larger the number after the "-" sign (for example, -4.00 is stronger than -1.00), the more significant the short-sightedness, and the more powerful your correction for distance vision needs to be.

The Plus Sign (+) for Correcting Long-sightedness

If the number is preceded by a plus sign (for example, +1.75), it indicates you are long-sighted (hyperopic). Long-sightedness is the opposite of short-sightedness: the eye has difficulty focusing, especially on near objects. This can lead to blurry near vision, but also headaches or significant eye strain, even when looking at distant objects, because the eye is constantly straining. As with short-sightedness, the higher the number, the stronger the correction.

Astigmatism: What Do "Cylinder" and "Axis" Mean?

If your prescription has numbers in the "Cylinder" (CYL) and "Axis" (AXE) columns, it means you have astigmatism, in addition to potentially being short-sighted or long-sighted.

Astigmatism is a very common vision defect that causes blurred and distorted vision at all distances. It's a result of an uneven curvature of the cornea or lens, which is shaped more like an oval than a circle. To understand, imagine a football (perfectly round) and a rugby ball (oval). An eye without astigmatism is like a football; an eye with astigmatism is like a rugby ball.

To interpret this optical prescription, you need to look at two values:

The Cylinder (CYL): This number (preceded by a + or - sign) indicates the power of the correction needed to compensate for the astigmatism. The higher the number, the more pronounced the astigmatism. If this box is empty, you do not have astigmatism.
The Axis (AXE): This number, between 0 and 180 degrees (°), does not indicate power but an orientation. It specifies the axis of the astigmatism, meaning the direction in which the lens must be positioned to correct the distortion.

A practical example: A line that reads OD: -2.00 (-1.25) 90° is read as follows:

For the right eye (OD):
A correction for short-sightedness of -2.00 (Sphere).
A correction for astigmatism of -1.25 (Cylinder).
The axis of this astigmatism is at 90 degrees (Axis).

The Addition (ADD) for Near Vision (Presbyopia)

At the bottom of the prescription or in a dedicated section, you might find a box labelled "Addition" or "ADD". This value only appears for people with presbyopia.

Presbyopia is a natural change in vision that usually appears after the age of 40. The eye's lens loses its flexibility, making it increasingly difficult to focus on near objects (reading a book, a menu, your phone).

The Addition is the power that must be added to your distance correction to allow you to see clearly up close. That's why it is always indicated by a positive number (e.g., ADD +2.00). This value is often the same for both eyes. This addition is used to make progressive lenses, which allow you to see clearly at all distances without having to change glasses.

Other Important Measurements on Your Prescription

Some other terms may appear, although they are less common. It is useful to know what they mean.

Pupillary Distance (PD)

Pupillary Distance is the distance, in millimetres, between the centres of your two pupils. This measurement is absolutely essential for the optician to correctly centre the lenses in your frame. Incorrect centring can cause visual discomfort and headaches. Sometimes the ophthalmologist writes it on the prescription, but more often, your optician measures it. At Lapaire, our qualified opticians are trained to measure your pupillary distance with the utmost precision, ensuring optimal comfort for your new glasses.

Prism Correction

If you see a "Prism" column or a triangle symbol (Δ), it means your prescription includes a prismatic correction. This is rarer. Prisms are used to correct eye alignment problems (strabismus) or double vision (diplopia). The prescription will indicate the prism power and its "Base" (direction: up, down, in, or out).

You now have all the tools to read a glasses prescription without panicking! Understanding what your prescription numbers mean is an important step in taking control of your visual health. You now know how to identify if you are short-sighted, long-sighted, have astigmatism, or presbyopia.

Now that you've cracked the code, the next step is to find the perfect pair of glasses for you. Our teams are here to help! Come and visit us at one of our many Lapaire branches across Africa. We offer a free eye test, and our opticians will be happy to advise you on choosing the lenses and frame that perfectly match your needs and your style.

This article is for informational purposes. For a personalized diagnosis, consult a Lapaire optician.

How to Read an Eyewear Prescription: The Lapaire Guide