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If you have a refractive error, you will be given an eyeglass or contact lens prescription at the end of your eye exam. This prescription includes the value of the parameters for dispensing corrective eyewear. The prescription itself is written in a standardized format so you can purchase eyeglasses from the vendor of your choice.
What are eyeglass prescriptions?
To most patients, eyeglass prescriptions may as well be written in Greek. They contain a number of different abbreviations, numbers, and terms that can be difficult to understand.
Eyeglass prescriptions include measurements that detail the power to which each eyeglass lens needs to be made to correct visual errors like nearsightedness, farsightedness, and astigmatism. Here are just a few of the abbreviations and terms commonly found in an eyeglass prescription:
DV = distance vision
NV = near vision
OD = oculus dexter (right eye)
OS = oculus sinister (left eye)
OU = oculi uterque (both eyes)
D = diopter
S = sphere (degree of nearsightedness or farsightedness)
C = cylinder (measures astigmatism in diopters)
Axis = orientation of the astigmatism
Reasons for prescriptions
Under Federal law, optometrists and ophthalmologists are required to provide lens prescriptions to patients at the end of an eye exam that includes refraction. This makes eyeglass prescriptions portable. One of the benefits of an eyeglass prescription is that it can be filled anywhere at any time. The language and terms are standardized so patients can obtain prescription eyewear whenever and wherever they need it.
How are prescriptions prepared?
Prescribing eyeglasses is a simple process. Optometrists measure refractive error with either a phoropter or an autorefractor. The refractive error is expressed by a measurement known as a diopter, which is represented by a capital D in a lens prescription. The greater the refractive error, the larger the number will be in the sphere and cylinder columns. The axis column measures the location of the irregularity.
For you, eyeglass prescription tests are simple, fast, and pain-free. At the end of the exam, the doctor gives you a lens prescription, which you can then take to an optician to purchase your corrective lenses.