How Do I Read My Eye Prescription?

If you wear eyeglasses, you must be familiar with the letters and numbers that appear on the prescription form. These digits are basically instructions that are essential in making glasses. Most people know that, but they do not know what they mean. Some tips can help you to read your prescription. While there may be some minor differences between different prescriptions, there is a general pattern.


Right Eye, Left Eye

Whether you have astigmatism, nearsightedness, or farsightedness, you will notice the letters OD and OS on your form. The first step in understanding what your prescription means is to know what the abbreviations O.D. and O.S. stand for. 

The abbreviations usually appear on the left side of the prescription form. O.D. stands for Oculus Dexter or right eye, while O.S. stands for Oculus Sinister or left eye. Some eye doctors use O.U. to signify both eyes, while others may use RE (right eye) and LE (left eye).


Sphere (SPH)

The sphere column or SPH is the lens power that is required to correct the vision. The power is measured in diopters for each eye. A minus (-) signifies nearsightedness, while a plus (+) signifies farsightedness. If the middle of the line is zero, meaning no correction is needed, the left and right sides are minus and plus. The further away you get from the middle means the stronger the prescription needed.


Cylinder (CYL)

The lens power in diopters is used for correcting astigmatism. The cylinder number indicates how much astigmatism you may have. If the patient does not have astigmatism, the column will remain blank. If astigmatism is present, it will be indicated just like the SPH, (-) for nearsighted astigmatism and (+) for farsighted astigmatism. 


Axis (Ax)

Much like the CYL, the Axis will only appear for astigmatism prescriptions. The numbers that appear in this column are written in degrees and not diopters, from 1 to 180 degrees. A prescription that has CYL must also include the Ax. The number will indicate where astigmatism appears on the eye.



This refers to added power. This is where any additional magnifying power will be indicated. Patients who require multifocal lenses will have this number. These are progressive or bifocal lenses where the bottom half of the lenses has added power. Some doctors will use PAL to indicate progressive lenses that are different from bifocals. 



The prescription may have a column for prism. Prism is used for correcting vision displacement or double vision. This special correction is built into lenses to fuse the double images into one clear image. The value appearing on the prescription indicates the number of diopters required to compensate for the alignment issues.



PD or pupillary distance indicates the distance between the pupils. Monocular PD indicates the distance from the pupil to the middle of the nose. Binocular PD measures the distance between the two pupils. 

Regular eye exams will help to ensure that you keep your vision sharp and your eyes healthy. It is important to know that a prescription for contacts will be different from the one for glasses. Contact lens prescriptions will include specific size measurements. This means that contact lens fitting is essential before getting contacts.

To know more about eye prescriptions, visit Urban Optics at our office in College Station, Texas. You can also call (979) 690-0888 to book an appointment today.

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