Common scenario. You just finished your eye exam and the eye doctor hands you a sheet of paper with a bunch of info that may as well be a foreign language you don’t know. You gather this much: you’re either near or farsighted. But that’s as much you can decipher. Don’t worry, it’s difficult to read an eyeglass prescription if you aren’t a doctor. Your prescription may look like this:

OD-2.00 SPH+2.00 add0.5 p.d. BD OS-1.00 -0.50 x 180+2.00 add0.5 p.d. BU

Here’s a quick tutorial + breakdown:

OD + OS: These are abbreviations for oculus dexter and oculus sinister, Latin terms for right and left eye. You may notice a column labeled “OU.”. This is Latin for oculus uterque meaning ‘Both Eyes.”

It is common practice for doctors to note the info for the right eye (OD) before the info for the left eye (OS).

Sphere (SPH): This stands for the amount of lens power, measured in diopters (D), which are prescribed to correct both near and farsightedness. If the number appearing under this is a minus sign (-), you are nearsighted: if the number has a plus sign (+) or is not proceeded by any sign, you are farsighted.

The term ‘Sphere’ means that the correction for your near or farsightedness is “spherical”, or equal in all meridians of the eye.

Cylinder (CYL): This indicates the amount of lens power needed for astigmatism. If this column is blank, you don’t have astigmatism.

The term “Cylinder” means that this lens power added to correct your astigmatism is not spherical. The number in the Cylinder column may be preceded with a minus sign (which corrects nearsighted astigmatism) or a plus sign (which corrects farsighted astigmatism).

Axis: This describes the lens meridian that contains no power to correct astigmatism and is defined with a number between 1 and 180. 90 corresponds to the vertical meridian of the eye, and 180 to the horizontal.

If you prescription includes cylinder power, it will also include an axis value, which follows the cal power and is marked with an x.

Add: This stands for the added magnifying power applied to the bottom part of mulitfocal lenses to correct presbyopia. the number appearing in this section is always a plus. In general it ranges from +0.75 and +3.00 D and will be the same for both eyes.

Prism: : This stands for the amount of prismatic power, measured in prism diopters (“p.d.” or a triangle when written in freehand), prescribed to compensate for eye alignments problems. Please note: we are sorry but we cannot accommodate this type of prescription. Please see your Optometrist.

Sphere power, cylinder power and add power always appear in diopters. They are in decimal form and written in quarter-diopter (0.25 D) increments.

Related Note: There is a rule which 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.