How to read your glasses prescription?

With the growing popularity of prescription glasses, the demand for trendy, beneficial and cheap online glasses is on an upward slope. But it all starts here: how to read your prescription?

The prescriptions use a standard format and a set of abbreviations, so that they can be interpreted internationally. An eyeglass prescription will look like this:

OD: -2.50 – 0.50 x 180

OS: + 1.00 DS

ADD: + 1.75 OU

Latin Letters:

The letters OD stand for "oculus dexter" and refer to the right eye, OS stand for "oculus sinister" and indicate the left eye and OU stand for "oculi uterque" and refer to both eyes.

Understanding Numbers:

A correct choice of prescription glasses is the result of correct understanding of the numbers in the prescriptions. As it is, prescriptions do have a lot of numbers.

The first number in our example is – 2.50. This is the "sphere" part of the prescription dealing with the "nearsightedness" (or myopia, an eye problem that causes distant objects look blurry) or "farsightedness" (also called hyperopia, which causes difficulty to clearly see the objects which are near). A minus sign (-) indicates negative powered lens to cure nearsightedness and a plus sign (+) indicates positive powered lens to correct farsightedness.

The next number is -0.50. This number represents the "cylinder" part of the prescription, also called astigmatism referring to the difference in curvature and power between two points on the eye, separated by 90 degrees. The minus sign denotes the presence of astigmatism.

The next number is x180, which is read as "axis 180". It indicates the angle in degrees, ranging from 0 to 180 denoting the position of the most positive meridian in an eye that has astigmatism.

For left eye, the number is +1.00 followed by DS (diopters sphere) which means that the left eye is without astigmatism and the left cornea’s shape is close to perfectly round compared to the right eye cornea’s slightly oblong shape.

Lastly, the ADD number +1.75 means the power that needs to be added to distance prescription so that a person has clear visibility at a close range.

Calculations:

To find out the total power needed, a small addition needs to be done. In the example above, for right eye, the prescription will be (-2.50 + 1.75) – 0.50 x 180 or -0.75 – 0.50 x 180 and for the right eye, +1.75 +1.00 = 2.75 DS.

Though it may look confusing at first, with practice and patience, a proper understanding of the prescription can be gained, which can prove really beneficial while looking for glasses online.