This article will help you with reading and understanding your eyeglasses prescription for you to use when buying new eyeglasses.
OD and OS
OD and OS are short terms of oculus dexter and oculus sinister which means “right eye” and “left eye” in Latin. Eyeglass prescriptions may have an “OU” column label or oculus uterque meaning “both eyes” in Latin.
The information for your right eye (OD) on your eyeglass prescription comes before the left eye (OS) information. It is written this way because doctors are facing you, seeing on their left the right eye first then your left eye second.
Eyeglass Prescription Parts
The following are the terms and abbreviations found on your eyeglass prescription:
Sphere (SPH)– specifies the amount of lens power prescribed for nearsightedness or farsightedness correction. It is measured in diopters (D). The number with a minus sign (-) in this heading indicates nearsightedness and the number with a plus sign (+) indicates farsightedness.
Cylinder (CYL)– specifies the amount of lens power for astigmatism. When there is no number under this column it means you have little to none astigmatism requiring correction.
The number in the cylinder column is followed by a minus sign for nearsighted astigmatism correction or a plus sign for farsighted astigmatism correction. In the eyeglass prescription, the cylinder power follows the sphere power.
Axis– it describes the lens meridian containing zero cylinder power for astigmatism correction with a number from 1 to 180. The number 90 signifies the eye’s vertical meridian, and the number 180 signifies the eye’s horizontal meridian.
The cylinder power in the prescription includes an axis value, following the cyl power and preceding an “x” if written freehand.
Add– this indicates the added magnifying power put on the lowest multifocal lens part for presbyopia correction. The number in this section always appears in a “plus” regardless of a plus sign indication. Normally, it ranges from +0.75 to +3.00 D having the same power for both eyes.
Prism– this indicates the prismatic power amount measured in prism diopters (“p.d.”) to make up for eye alignment issues. Not all eyeglass prescriptions have prism.
The prism amount is expressed in either metric or fractional form, and its direction is indicated by writing down the relative position of its thickest stage. The abbreviations used for prism direction are BD= base down; BO= base out; BU= base up; BI= base in.
The cylinder power, sphere power, and add power are found in diopters and are written in decimal form, in one fourth diopter increments.
Axis values which are written in whole number form (1 to 180) denote only a meridional location and not a power.
Additional Information– eye doctors might include in your eyeglass prescription some specific lens recommendations, like anti-reflective coating, photochromic lenses, and progressive lenses, for better vision correction.