Your glasses prescription explained
Ever wondered what the numbers and symbols on your glasses prescription mean? Understanding your prescription is key to getting the perfect pair of glasses. Here’s a simple guide to decoding your prescription and ensuring you order the right lenses online.
+ or - Symbol
The “+” symbol indicates a prescription for farsightedness (Hypermetropia), meaning you struggle to see close-up objects.
The “–” symbol is used for nearsightedness (Myopia), meaning distant objects appear blurry.
These symbols refer to how light focuses inside your eye—either too close (nearsightedness) or too far (farsightedness).
Short and long sighted
If you see a (–) symbol next to or above a number in the (SPH) section - you have a short sighted prescription. Although you can normally see things close up or sometimes really close up. Far away distances would be a blur.
If you see a (+) symbol in the (SPH) section next to or above a number, you have a long sighted prescription. This doesn’t always mean you can see things far away and need a correction for close up tasks such as reading. As sometimes long sighted people struggle to see things far away too.
The phrases simply refer to where light when entering the eye focuses in relation to the retina (the light sensitive part at the back of your eye).
Far sighted the light focuses too far or if you are short sighted the light focuses too short.
Read more about how the eye works…
Dioptre
A Dioptre is main measurement used in optics and is based on focal lengths measured in meters. For example a 1.00 Dioptre spectacle lens will focus 1 meter away while a 10.00 Dioptre spectacle lens will focus in 0.1 meters (10cm)
If you fancy working out the focal length of your own prescription simply use the equation below:
1m divided by the power of your prescription (found in the SPH part).
Example: If you have a 2.50 in this part, 1 divided by 2.50 = 0.4m (40cm)
SPH (Sphere)
SPH (Sphere) is the strength of your prescription and is the first part of your glasses prescription. The higher the SPH value, the stronger the lens needed to correct your vision. A positive number (+) means you are farsighted, while a negative number (–) means you are nearsighted. If there is no prescription needed, you may see an infinity symbol (∞), which represents a 0.00 value.
For example:
-1.75 = Nearsighted (SPH)
+2.25 = Farsighted (SPH)
CYL (Cylinder)
If your prescription includes CYL, this means you have astigmatism. Astigmatism is a common condition where the shape of your cornea (the front part of your eye) is irregular, causing blurred or distorted vision. The higher the number under CYL, the more correction is required for astigmatism.
AXIS
AXIS refers to the orientation of your astigmatism correction and ranges from 1 to 180 degrees. It tells your optometrist the precise angle at which your astigmatism is corrected, ensuring your glasses align perfectly for clear vision.
ADD
As we age, we often experience presbyopia, a condition that makes it harder to focus on close-up objects. The ADD value on your prescription helps to correct this by adding extra power for reading or other close tasks. The ADD number will always be positive (+) and increases with age as your near vision changes.
Read more about Presbyopia here…
PRISM
Not all prescriptions have this section, but if it does, it’s for correcting eye alignment issues such as double vision or muscle imbalance. Prisms help align the eyes so they work together properly. If you have a prism correction, you’ll also see a “base” value, which indicates the direction of the prism (e.g., IN, OUT, UP, DOWN).
Read more about muscle imbalance here…
BASE
A Prism is a triangle Δ - light always bends towards the Base and will normally be written as either IN, OUT, UP or DOWN but can sometimes be written as a number between 1 to 360.
PD – Pupil Distance
Your PD, or Pupil Distance, is the distance between your pupils in millimeters (mm). It’s crucial for ensuring your lenses are aligned properly for comfortable and clear vision. Your optician may not include this measurement in your prescription, so you may need to have it measured separately when ordering new glasses.
Read more on how we measure your pupil distance when buying glasses from ourselves.
FAQ
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SPH stands for "Sphere" and indicates the power of your prescription. Positive values (+) mean you are farsighted, and negative values (–) mean you are nearsighted.
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SPH corrects general vision issues like nearsightedness or farsightedness, while CYL is for correcting astigmatism, which causes blurry or distorted vision.
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AXIS refers to the angle at which your astigmatism correction is applied, ranging from 1 to 180 degrees.
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ADD is the extra power required for reading or close-up tasks. It’s commonly added to prescriptions as we age and experience presbyopia, a condition that affects near vision.
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PD (Pupil Distance) is the distance between your pupils and ensures that your lenses are aligned correctly. It’s essential for ordering custom glasses but is not usually provided on your prescription.
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No, Prism is used only if you have an eye muscle imbalance or issues with double vision. If it’s included, it will also specify a "base" direction to guide the prism correction.
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The SPH value varies depending on whether you are nearsighted or farsighted. Typically, SPH values for nearsightedness (Myopia) range from -1.00 to -6.00, and for farsightedness (Hypermetropia), they range from +1.00 to +6.00. However, the exact value will depend on your specific vision needs.
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CYL (Cylinder) and AXIS are included if you have astigmatism. The CYL value corrects the shape of your eye, while the AXIS value tells your optometrist where to apply the correction. If you don’t have astigmatism, these values won’t appear on your prescription.
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If your prescription is recent (typically within 1-2 years), you can usually use it to order new glasses. If it’s outdated, we recommend getting a new eye test to ensure your vision correction is still accurate.
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Single vision lenses are for one distance (either near or far)
Bifocal lenses have two prescriptions (one for distance and one for reading).
Progressive lenses provide a smooth transition between multiple prescriptions without visible lines, making them ideal for presbyopia correction.
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Progressive lenses are typically recommended for people over 40 who experience difficulty focusing on nearby objects, a condition known as presbyopia. If you find yourself holding books, newspapers, or smartphones farther away to read, progressive lenses could be the solution.
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PD is a precise measurement between your pupils, typically accurate to within 1mm. A small mistake in PD measurement can affect the clarity of your vision through your lenses, so it's important to get it right. Many opticians can measure this for you if it’s not provided on your prescription.
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DS stands for “Dioptre Sphere,” indicating that there is no astigmatism correction required in your prescription. If you see DS, it means your prescription is purely for nearsightedness or farsightedness without the need for cylindrical correction.
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Opticians may write your prescription in either fractions or decimals. For example, -1 ½ might be written as -1.50. The meaning is the same; it’s just a different format. Either way, the number indicates the power of your lens correction.