How to read a contact lens prescription (2024)

FAQs

How do I interpret my contact lens prescription? ›

The number that's listed will be measured in diopters, a term that refers to corrective lens strength. It will be preceded by a plus sign (+) if you're farsighted or a minus sign (-) if you're nearsighted.

While your glasses prescription can serve as a starting point, you will need a contact lens consultation to get the correct contact lens prescription. This will detail the base curve and diameter of the lens, what kind of material or brand to use, and how long the prescription will last.

The sphere column is often abbreviated as SPH. This is the lens power needed to fix your vision. A minus sign (−) next to the number means nearsightedness (you see better up close and need distance correction). A plus sign (₊) indicates you are farsighted (you see better far away and need your near vision corrected).

In optometry, the term 'Plano' means zero or nil. Thus, Plano lenses are lenses without any distance prescription strength. They are simple optical lenses that provide no corrective spherical power.

Astigmatism is measured in diopters. A perfect eye with no astigmatism has 0 diopters. Most people have between 0.5 to 0.75 diopters of astigmatism. People with a measurement of 1.5 or more typically need contacts or eyeglasses to have clear vision.

To switch from glasses to contact lenses, you cannot directly convert your glasses prescription. Also, trying to calculate your lens prescription yourself is a huge mistake. Not everyone who wears glasses can wear contacts. You need a separate eye exam before making the switch.

Hint: The equation that relates the focal length of a spherical lens to the index of refraction of the lens and the radii of curvature for the front and back surfaces is called the Lens Maker's Equation: 1/f = (n - n_o)(1/r₁ - 1/r₂), where n_o = 1.00 for air.

Eyeglass strength is measured in diopters. If your prescription reads -1.00, that means your eyeglasses need 1 diopter of strength to correct nearsightedness. If your prescription reads +2.50, your eyeglasses need 2.5 diopters of strength to correct farsightedness.

If you have a minus number, like -2.75, it means you're short-sighted and find it more difficult to focus on distant objects. A plus number indicates long-sightedness, so objects up close appear more blurred or close vision is more tiring on the eyes.

Thankfully, if you have a pretty basic prescription (meaning they're not bifocals, progressives or co*ke-bottle lenses), there's a free tool from GlassesUSA.com that can scan your current glasses. I took it for a spin with my son's glasses and the results matched his current prescription.

What is a bad astigmatism number? ›

Between . 75 and 2 diopters is considered mild astigmatism. Between 2 and 4 diopters is moderate astigmatism, and 4 or more diopters is considered significant or “bad” astigmatism. Generally, eyes with 1.5 diopters of astigmatism or more require correction.

Your prescription details can be found on the side of your contact lens box. If you don't have your box, we're happy to contact your eye care provider to get a copy of your prescription for you.

You can find the power in the “PWR/SPH” column of your prescription. This field might also be labeled “Sphere” or “Power.” The corresponding number will be positive or negative, and represents the diopters of vision correction needed to counteract a refractive error in your eye and help you see clearly.

There is no way to convert a glasses prescription to a contact lens prescription, and vice versa.

The Numbers. The numbers you see represent diopters, the units used to measure the correction of the lens (the focusing power) required by each of your eyes. Sometimes diopter is abbreviated to “D.” On a glasses prescription, 0.00 (zero focusing power needed) represents good vision.

This important number, typically between 8.3 and 9 millimetres in soft contact lenses, calculates how a contact lens will sit on the curvature of your eye's surface. If this value is not appropriate for your cornea, even modest changes can result in discomfort and poor vision.

Positive numbers on an eye prescription indicate they are correcting farsightedness, while negative numbers correct shortsightedness. A larger number suggests a stronger prescription. Many people wonder how bad their eye prescription is, especially as the numbers and symbols are often difficult to interpret.