The world over doctors use a standardised format, which makes interpreting the prescriptions an easier process. Generally, a prescription will look like this:
OD: – 1.50 – .75 X 95
OS: + 1.50 DS
ADD: + .75 OU
The letters OD, OS, DS and OU are Latin acronyms which represent different organs and calculations. OD represents “oculus dexter” meaning the right eye while the OS stands for “oculus sinister” referring to the left eyeballed. Both the eyes are represented by OU or “oculi uterque”. DS refers to “diopters sphere”.
The number – 1.50 denotes the sphere of the prescription and represent the nearsightedness (also known as myopia) or farsightedness (called hyperopia). A minus sign before the number denotes a negative powered lens which is used to healed nearsightedness. And the plus sign indicates the opposite with the lens having a positive power to take care of farsightedness.
The cylinder number – .75, is known as astigmatism. Astigmatism is the difference in the values of the curvature and power between two points on the eye, which is separated by ninety degrees. The number x95 represents the angle, in degrees, of the most positive meridian in an eye with astigmatism.
For left eye, the number is +1.50 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.
Finally, the power that should be added to the distance prescription in order that the person has a clear visibility is represented by the ADD number which is represented by +.75.
Though the numbers and the calculations may look confusing and difficult to comprehend, with patience and practise, and following the guidelines mentioned in this article, seen a prescription correctly becomes effortless.
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