When you go to the eye doctor to measure your eyesight to get new eyeglasses, you will be given a paper with numbers, letters, and symbols. This is your eyeglasses prescription.
Not everyone knows how to read these prescriptions properly. Today’s article will guide you to read your eyeglasses prescription.
OD & OS: What does this mean?
- OD represents the right eye. It is short for Oculus Dexter, Latin for right eye.
- OS represents the left eye. It is short for Oculus Sinister, Latin for the left eye.
- OU might sometimes be written in a column in your prescription. OU is short for Oculus Uterque, meaning both eyes in Latin.
These terms are not only standard in eyeglasses prescriptions but also for contact lenses and eye medicines. Some doctors prefer using RE (right eye) and LE (left eye) instead of OD and OS.
The term “sphere” indicates the amount of lens power measured in diopters (D) needed to correct nearsightedness or farsightedness. The term ‘sphere’ means the correction is ‘spherical’ or equal in all the meridians of the eye.
You are nearsighted if a (-) symbol comes with the number. If the number is preceded by a (+) sign, you are farsighted. So, for example, you see in the sphere section +5.00 — this means there are five diopters of farsightedness.
Number zero means your eyes need no correction. Thus, the further you are from zero, on either the minus or plus side, the higher your prescription is and the lower your uncorrected vision.
The cylinder number indicates the power needed to correct astigmatism. If this box is empty or reads 0, astigmatism is not present or it’s so small it doesn’t need to be corrected. The cylinder power is always a minus number.
The term ‘cylinder’ means that this lens power is not spherical.
If you have astigmatism, your eye is shaped more like a rugby ball instead of a football, and this needs to be corrected in this way.
If your prescription has a cylinder power, it must be followed by an Axis number. Axis indicates the location of astigmatism on the cornea. The axis, a number from 1 to 180, is the lens meridian that is 90 degrees away from the meridian that contains the cylinder power to correct astigmatism.
The number 90 refers to the vertical meridian of the eye, while 180 corresponds to the horizontal meridian.
‘Add’ refers to ‘Addition’ or the added magnifying power applied to the bottom part of multifocal lenses to correct presbyopia. Presbyopia is a part of aging, indicating the gradual loss of your eye’s ability to focus on nearby objects.
The number appearing in the Add section of the prescription always goes with a “plus” power. It typically falls between +0.75 to +3.00 D and will be the same power for both eyes.
Prism is designed to correct vision for people with diplopia or double vision. These conditions make patients see two distinct images of one object. The prism helps align the two images so that only one image is visible.
Prism is not always present in eyeglasses prescriptions. When it is, the amount of prism is calculated in either metric or fractional English units.
The direction of the prism is indicated by noting the relative position of its “base.”
- BU = base up
- BD = base down
- BI = base in
- BO = base out
Example of Reading an Eye Prescription
OD = the right eye:
- -5.00 D sphere for nearsightedness correction.
- There are no numbers in the cylinder power or axis section, which means the patient doesn’t have astigmatism.
OS = the left eye:
- -5.50 D sphere for nearsightedness correction.
- -1.00 D cylinder for the astigmatism correction, with an axis at 180 degrees.
- Add section is +3.00 D for the correction of presbyopia, the ‘reading correction’
- Prismatic correction of 0.5 prism diopter in each eye.
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