How Do Eye Prescriptions Work?

What are those letters, numbers, and +/- signs actually saying about your vision?

If you wear eyeglasses or contact lenses, then you’ve likely taken a glance at your prescription before only to look away in a state of confusion. In truth, eye prescriptions are designed mainly as a form of communication between your eye doctor and the manufacturer of your eyewear – but that doesn’t mean they’re incomprehensible. With a little bit of background, anyone can become a prescription-reading expert.

Here are the main elements of eye prescriptions and what they mean.

Abbreviations

Your eye prescription hosts a number of abbreviations that appear utterly meaningless without any context. Two of the most important abbreviations are OS and OD. OS is short form for oculus sinister, the Latin term for your left eye. OD stands for oculus dexter, which is Latin for your right eye. Optometrists use these abbreviations to communicate to eyewear producers the prescription that belongs on each lens. Other common abbreviations include SPH, or sphere; DV, or distance vision; NV, or near vision; and PD, or pupillary distance.

Plus and Minus Signs

Rest assured, the presence of the ‘+’ and ‘-’ symbols is not a request to break out a calculator. Rather, these signs indicate whether you are nearsighted or farsighted. A ‘+’ sign before the number means you have myopia (nearsightedness), whereas a ‘-’ sign means you have hyperopia (farsightedness). Knowing what refractive error your eyes have lets the lens maker know, in a manner of speaking, the direction in which to correct your vision.

Numbers

Underneath the abbreviations and behind the +/- signs are decimals that represent the degree of correction your eyes require. This unit of measurement is called a diopter, which measures the refractive power of your eyes. So if your prescription reads “OS: +3.00”, it is communicating that your left eye has three diopters of nearsightedness. The eyeglass manufacturer uses this measurement to determine the thickness of the lenses.

Astigmatism

If you have an astigmatism in either or both of your eyes, then you’ve probably noticed additional numbers and abbreviations on your prescription. For example, the word ‘axis’ and a number between 1-180 represents the exact location of the astigmatism on the eye. The word ‘cylinder’ is also present, heading a decimal that specifies to the glasses makers precisely how much lens power is required to correct the astigmatism.

Contact Lenses

Contrary to popular belief, your eyeglass prescription is not identical to your contact lens prescription. The reason for this is that, whereas eyeglasses sit in front of your eyes, contact lenses rest directly on the surface of your eyes, requiring them to have additional measurements. These measurements are taken during what is called a contact lens fitting, and they include the diameter and base curve to match the size and shape of your eyes. Contact lens prescriptions also include the name of the manufacturer, the type of lens, and an expiration date.

The Takeaway

Prescriptions are the tools doctors use to ensure that glasses and contact lens producers understand the exact needs of your eyes when making your eyewear. Accuracy on the part of optometrists and manufacturers is key, but it is important to note that, as your eyes undergo their natural change, your prescription will need to be adjusted accordingly.

Keeping your prescription up to date can only be accomplished by attending your yearly eye exam. Sterling Vision is composed of some of the best optometrists in the field today, each of them equipped with the tools and experience needed to measure your vision and produce the most accurate prescription possible. To schedule an appointment with us, call 541-262-0597 or schedule online.