With the rising use of prescription glasses, online stores are becoming the hotspots for buying cheap eyewear. The choice of prescription glasses offered by these online stores is diverse and displays a milieu of colour combinations. But at all these stores, you have to put in your prescription details so that the lenses can be made according to them. In this scenario, the knowledge of what your prescription means, can prove to be of great help. Though the prescription might look confusing, it is simple enough to be understood easily.

To make the prescription easy to interpret, a standard format and a set of common abbreviations are used. This makes the prescription to be understood internationally. A common eyewear prescription will look like the following: OD: - 2.00 – 0.25 X 145 OS: +1.25 DS ADD: +1.50 OU

The abbreviation OD stand for "oculus dexter" and it indicates the right eye. Likewise, OS stands for "oculus sinister" and refer to the left eye, while the letters OU stand for "oculi uterque" which refer to both the eyes.

The first number in the example (- 2.00) represents the "sphere" part of the prescription which deals with the myopia (nearsightedness) or hyperopia (farsightedness). A minus sign indicates negative powered lens used to cure nearsightedness and a plus sign means the opposite.

The cylinder part of the prescription is referred by the next number (-0.25). This is known as "astigmatism" and it is the difference in curvature as well as power between two points on the eye, which is separated by 90 degrees. The presence of astigmatism is indicated by the minus sign.

X 145, or "axis 145" is the angle measured in degrees, and denotes the position of the most positive meridian in an eye that has astigmatism. The angle ranges from 0 to 180.

For left eye, the +1.25 is followed by an abbreviation DS (diopters sphere) which indicates that the left eye is without astigmatism. Finally, +1.50 is the power that needs to be added to the distance prescription. This will enable a person to have a clear visibility at close range.

For the right eye, the prescription will be (-2.00 + 1.50) – 0.25 X 145 or – 0.50 – 0.25 X 145 and for the left eye, +1.50 + 1.25 = 2.75 DS.