An optometrist will take several different measurements when prescribing eyeglasses. These numbers, which will appear on the eyeglass prescription, describe what kinds of problem that each eye has. These measurements also provide instructions for anyone who is making a lens, so that the proper lenses can be made without a new eye exam.
Step 1
Identify the measurements for each eye. Your eyeglass prescription is separated into a series of three measurements for each eye. The right eye is typically designated as "oculus dextrus" or sometimes just "O.D." Other times, the optometrist may simply write "R.E." (for right eye). The measurements for the left eye will be designated "oculus sinister," or O.S. (or L.E.). In general, the numbers for the right eye will be listed first, so in the absence of any designation, you can assume that the first set of numbers is for the right eye.
Step 2
Identify the "sphere" number for each eye. The sphere number is a measurement of near- or far-sightedness. It is typically given in terms of diopters. Negative numbers mean that the eye is near-sighted, and positive numbers indicate far-sightedness. The eyeglass lens will then be shaped to correct the near- or far-sighted eye.
Step 3
Find the "cylinder" number. This number, which is given in diopters in each eye, measures astigmatism. Astigmatism occurs when parts of the lens of the eye are more curved than other portions. Next to the cylinder measurement in each eye is the "axis" number, which is given in degrees. It describes the location of the abnormal curvature.
