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Are Glasses and Contact Prescriptions the Same?



Glasses and contact prescriptions are NOT the same.

More Info: Not only does the power change slightly between prescriptions, but contact lens prescriptions require several measurements that glasses do not.

Contact Lens Prescriptions versus Eyeglass Prescriptions

Both prescriptions will include measurements of power to correct myopia (nearsightedness) or hyperopia (farsightedness). Measured in diopters, myopia will appear on a prescription as a negative number and hyperopia as a positive number. [1] The numbers run between -10 and +10 and will dictate the power of the prescription. The vision requires more correction in relation to their distance from zero. The right eye, designated as OD in a prescription, may have one power, while the left eye, designated as OS in a prescription, may have another. [2]

Cylinder can be found in both prescriptions as the measurement for correcting astigmatism.  The axis may be present along with the cylinder to denote the location of the astigmatism. [3]

Add is another measurement that may be found in both prescriptions. Add is the additional magnifying power for bifocals. [4]

How Do They Differ?

Measurements called the base curve and diameter are necessary only to contact lenses because they sit directly on the eyeball.  The diameter dictates how big the lens will be while the base curve measures the curvature of your cornea.  [5]

These measurements are extremely important because a lens that is too tight or does not fit properly can severely damage your eyes.  This is why those that choose to wear decorative lenses still require a contact lens prescription even if they have perfect vision. [6]

Why Do They Differ?

As well as the necessary additional measurements required for a correct fit with contact lenses, other parts of the prescription may change.  Because contact lenses sit directly on the eyeball whereas eyeglasses sit about 12 mm away, a slight modification in the power of the prescription is necessary.  [7]  The higher the prescription the greater the difference between a prescription for glasses and one for contact lenses. [8]


Is Your Contact Lens Prescription the Same as Your Eyeglasses Rx?

[2][3][4] Just Eyewear
How to Read Your Eyeglass Prescription

[5][8] David Drucker MD.,PC
A Glasses Prescription Is Not a Contact Prescription

[6] FDA
Decorative Contact Lenses: Know the Risks

Resource: All about Vision
Understanding Your Contact Lens Prescription

Resource: All about Vision
How to Read Your Eyeglass Prescription

Expert Opinion

“The numbers on the glasses prescription and contact lens prescription may look very different, especially if you have a big prescription. This is simply due to optical mathematics.”

Contact Lenses  Casey Eye Institute, Oregon Health & Science University


Glossary of Terms

Astigmatism: a defect of an optical system (as a lens) causing rays from a point to fail to meet in a focal point resulting in a blurred and imperfect vision.
Merriam Webster Dictionary

Diopter: a unit of refractive power, which is equal to the reciprocal of the focal length (in metres) of a given lens.
Oxford Dictionary

Farsightedness: able to see clearly only objects that are not close.
Cambridge Dictionary

OD: abbreviation for Latin oculus dexter, meaning right eye.
Just Eyewear

OS: abbreviation for Latin oculus sinister, meaning left eye.
Just Eyewear

Nearsightedness: someone who is nearsighted cannot see objects clearly when they are far away.
Cambridge Dictionary

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