Interpreting Your Prescription
An eyeglass prescription is an order written by an optometrist or ophthalmologist specifying the corrective power and other parameters needed to produce corrective lenses. The following information is provided to better help you understand each part of your eyeglass prescription.
OD–Oculus Dextrus (latin), meaning right eye
OS–Oculus Sinister (latin), meaning left eye
OU–Oculus Unitas (latin), meaning both eyes
PD-Pupillary Distance, meaning the distance between the centers of the pupils
SPH-Spherical correction in all meridians
CYL-Cylindrical correction of astigmatic refractive error in a meridian specified by the prescribed axis
AXIS-Present only if the is a CYL value. The axis is the lens meridian that is 90 degrees away from the meridian that contains the cylinder power.
ADD-This is the added magnifying power applied to the bottom part of multifocal lens to correct presbyopia.
PRISM/BASE-This is the amount of prismatic power, measured in prism diopters, prescribed to compensate for eye alignment problems. When present the direction of the prism is indicated noting the relative position of its “Base” or thickest edge. Four abbreviations are used for prism direction: BU=Base Up; BD=Base Down; BO=Base Out(towards the ear); BI=Base In(towards the nose)
An Example of an Eyeglass Prescription
Now that you know the terms used in your Rx let’s look at an example.
Here is a sample eyeglass Rx:
OD -3.00SPH +2.50 ADD 0.75 P.D. BU
OS -2.00SPH -1.00CYL X 180 +2.50 ADD 0.75 P.D. BD
In this case, the doctor has prescribed -3.00D sphere for the correction of myopia in the right eye (OD). There is no astigmatism correction for this eye, so no cylinder power or axis is noted. This doctor has elected to add “SPH” to confirm the right eye is being prescribed only spherical power. (Some doctors will add “DS” for “diopters sphere” others will leave this area blank.)
The left eye (OS) is being prescribed -2.00D sphere for myopia plus -1.00D cylinder for the correction of astigmatism. The CYL power has its axis at the 180 meridian, meaning the horizontal (180-degree) meridian of the eye has no added power for astigmatism and the vertical (90-degree) meridian gets the added -1.00D.
Both eyes are being prescribed an “ADD” power of +2.50D for the correction of presbyopia, and this eyeglass prescription includes a prismatic correction of 0.5 prism diopter in each eye. In the right eye, the prism is base up (BU); in the left eye, it’s base down (BD).
An Eyeglass Prescription is NOT a Contact Lens Prescription
Eyeglass and contact lens prescriptions are different. An eyeglass prescription does not contain information that is necessary to a contact lens prescription. That additional information can only be obtained during a contact lens consultation and fitting.
The power of an eyeglass prescription is modified when determining the contact lens power due to the fact that eyeglass are worn from some distance from the surface of the eye, whereas contact lenses are worn directly on the cornea of the eye. In addition, a contact lens Rx must specify the base(central) curve of the back surface of the contact lens, the lens diameter and the specific brand name of the lens.
Your Eyeglass Prescription is YOURS TO KEEP
The Federal Trade Commission’s Prescription Release Rule became law in 1980. This rule requires eye doctors (both optometrists and ophthalmologists) to give patients a copy of their eyeglass prescription at the end of an eye exam that includes a refraction.
The rule is intended to protect the “portability” of your eyeglass prescription thus allowing you to use it to buy glasses from the vendor of your choice.
Your eye doctor MUST give you a copy of the prescription whether or not you ask for it. Eye doctors may NOT condition the release of your prescription on your agreement to purchase eyeglasses from them, nor may they charge you an extra fee to release your prescription. They also may NOT DISCLAIM LIABILITY FOR THE ACCURACY OF THE PRESCRIPTION if you purchase eyeglasses elsewhere.
If you feel your eye doctor has violated the rule or you want information on other consumer issues, you can contact the Federal Trade Commission at 1-877-FTC-HELP (1-877-382-4357).
Our optician will be happy to discuss any questions you may have. Please stop by or schedule an appointment today. Choose your lens style