Receiving a new pair of glasses is always an exciting moment, but for many, the prescription handed out by the Optometrist can seem written in another language. These numbers and technical abbreviations are not always easy to understand. Yet they play an essential role in manufacturing your glasses or contact lenses. So, how do you decipher this mysterious information?
The sphere (SPH)
The term “sphere” on your prescription, often abbreviated to SPH, indicates the corrective power needed to correct your vision. If you're myopic (you can't see clearly at a distance), the number will be preceded by a “-” sign. Conversely, if you're hypermetropic (you see blurred at close range), this number will be preceded by a “+”. The further the number is from zero, the stronger the correction.
Example:
• SPH -2.00 means you need a correction of 2 diopters to improve your distance vision (myopia).
• SPH +1.50 corrects poor near vision (hyperopia).
The cylinder (CYL)
Cylinder or CYL refers to astigmatism, a visual disorder caused by an irregular curvature of the cornea or lens. This curvature affects how light enters the eye, creating blurred vision at all distances. If you have a number in the CYL column, your eyes require a specific correction for astigmatism. A negative number indicates correction for myopia-related astigmatism, while a positive number is associated with hyperopia.
Axis (AXIS)
The axis is directly related to astigmatism. It indicates the orientation of the cylinder on your lenses, expressed in degrees (from 0° to 180°). This allows you to position the correction where your eye needs it.
Example:
- If the prescription indicates CYL -1.25 and AXE 90, you have mild astigmatism, and the correction is applied on a 90° axis.
Addition (ADD)
If your prescription mentions an ADD, it's usually for progressive or bifocal lenses. This number represents the additional power required for near vision. It is mainly added to the basic correction to help people with presbyopia read or perform close-up tasks. This number is generally positive, ranging from +0.75 to +3.00.
Pupillary Distance (PD)
Although often overlooked, pupillary distance, or PD, is essential for the manufacture of eyewear. This number corresponds to the distance, in millimetres, between the centers of your pupils. Precise measurement means that corrective lenses can be centred on your eyes for maximum comfort and effectiveness.
Why is it important to understand your prescription?
Understanding these terms and numbers can help you communicate better with your Optician and Optometrist. Understanding your prescription also gives you more control over your visual health and the corrective solutions that work best for you.
Finally, remember that every item on your prescription impacts your vision. Don't let the numbers intimidate you. If you have any questions, don't hesitate to ask your Optometrist to explain them in detail!
By mastering the basics of your prescription, you'll be able to see well and make informed decisions about your vision care.
