Eyeglasses correct many different types of refractive errors, or sight problems, including nearsightedness, farsightedness or astigmatism. Trying to understand the numbers on an eyeglass prescription requires understanding the measurements optometrists use when fitting you for corrective lenses.
Other People Are Reading
The numbers on your prescription are given in dioptres, abbreviated "D," which measure the focusing power, or amount of correction, that each of your eyes require.
O.S. and O.D.
Optometrists use the Latin abbreviations O.S. and O.D. to differentiate between your eyes. O.S. stands for oculus sinister, and refers to your left eye, while O.D., or oculus dextrus, refers to the right eye.
Positive and Negatives
Generally, your prescription will show a number for O.S. and O.D. (given in dioptres). The farther this number is on a number line from zero, the more correction your eyeglasses should provide. A plus sign means the eye is farsighted, while a minus sign means the eye is nearsighted.
This positive or negative number for each eye is called the spherical value, or the degree of nearsightedness or farsightedness you have. It is abbreviated as "S."
If you have an astigmatism, the optometrist will also measure its degree and severity. The higher the number (given in dioptres) marked as the cylinder of astigmatism, (abbreviated "C"), the more astigmatism there is in that eye.
An astigmatism is also measured in terms of its axis, which is a number between 0 and 180 that refers to the orientation and placement of the astigmatism on that particular eye.
- 20 of the funniest online reviews ever
- 14 Biggest lies people tell in online dating sites
- Hilarious things Google thinks you're trying to search for