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How to Read the Prescription from your Optometrist

Understanding Your Eye Prescription: A Comprehensive Guide


Navigating your eye prescription might seem daunting with its array of abbreviations and numbers. But fear not, decoding this information is simpler than it appears!


Whether you're new to wearing prescription glasses or a seasoned wearer, grasping your eye prescription is a valuable skill.


Deciphering the Numbers:

When perusing your prescription, you'll encounter the abbreviations OS and OD.

OS (oculus sinister) signifies your left eye.

OD (oculus dextrus) signifies your right eye.


Although it may seem archaic, these Latin terms persist in the medical realm. The OS and OD numbers denote the strength your lenses should possess for each eye, measured in diopters. A higher number indicates a stronger prescription.


Understanding the Signs:

Additionally, beside the OS and OD numbers, you'll notice plus and minus signs.

Plus (+) indicates farsightedness, difficulty in seeing close-up objects.

Minus (-) indicates nearsightedness, challenges in seeing distant objects clearly.

Typically, the signs for the SPH (or CYL) of the left and right eyes match, but exceptions exist where they differ.


Decoding Astigmatism:

If your prescription comprises three numbers, it signifies astigmatism, a condition where the cornea isn't perfectly round.


S or SPH measures the diopter strength of your general prescription.

C or CYL measures the diopter strength of your astigmatism. Higher numbers denote a more significant astigmatism.


The "axis" indicates the degree of your astigmatism, ranging from 0 to 180.


Understanding the "ADD" Value:

If an "ADD" value appears, it denotes additional magnification recommended for presbyopia, a natural aging effect affecting most people over 40.


ADD values are measured in increments of +0.25 for both eyes, often requiring progressive lenses to aid with both reading and distance vision.


However, not everyone with presbyopia needs a prescription; some may opt for reading glasses. Monitor signs indicating a need for reading glasses and consult your doctor for personalized advice.




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