How to Read Your Prescription

If you've ever worn glasses, you've probably seen the jumble of letters and numbers that make up your prescription. While these look like mysterious codes, they actually hold the key to crafting the perfect lenses for your eyes. Let's delve into what each part of your prescription means.

Sample prescription form with key areas highlighted

Right Eye vs. Left Eye: Decoding the Acronyms

On your prescription, you'll notice two main acronyms, one for each eye:

• O.D. (Oculus Dexter): This stands for your right eye.
• O.S. (Oculus Sinister): This refers to your left eye.

These terms have a bit of Latin flair, making them sound more complex than they are!

What Does "Sphere (SPH)" Mean?

The "Sphere" or SPH column specifies the lens power required to correct your vision. Here's how to interpret it:

• Minus Sign (−): Indicates nearsightedness, meaning you see better up close and require distance correction.
• Plus Sign (+): Signifies farsightedness, meaning you see better at a distance and need help with near vision.

Lens power is measured in diopters, denoted as D. For instance, if you see −9.00 D in the SPH field, you have 9 diopters of nearsightedness. Imagine this as a number line, with zero being perfect vision. The farther you stray from zero, the stronger your prescription needs to be.

The Mystery of "Cylinder (CYL)"

The CYL number relates to astigmatism, a condition where the eye's curvature isn't perfectly round. Picture a normal eye as a basketball, maintaining the same curve no matter how you rotate it. An eye with astigmatism resembles an egg or a North American football—having different curves along different axes. The CYL value adjusts for this discrepancy, giving you clear vision.

Understanding the Axis

The Axis is a number between 1 and 180 that pinpoints where astigmatism is located on your cornea. It tells you the angle at which the astigmatism lines up, guiding the correction to where it's needed.

The "Add" Field

The Add field is where additional lens powers are listed. For those over 40 who don't want to juggle multiple pairs of glasses, bifocals are a popular choice. The lower portion of these lenses assists with reading, providing clarity for close-up tasks.

Lens Power for Prism

Some prescriptions include a section for prism, a specialized correction for individuals experiencing double vision (seeing two images of the same object). The prism merges these images into one, offering a clear, singular view.

What About Contact Lenses?

Contact lenses require a different prescription than eyeglasses because they sit directly on the eye. A contact lens prescription includes specific measurements for size and brand, ensuring a proper fit. Before getting contacts, you'll need a "contact lens fitting" to determine the best options for your eyes.