Your eyes are already fuzzy from dilation; now your optometrist or ophthalmologist has thrown a bunch of numbers and terms at you, such as nearsighted or farsighted or astigmatism. Then, as your doctor attempts to translate this onslaught of information into layman’s terms, your eyes latch on to abbreviations, including OD, OS, SPH and CYL. Before your dilated eyes and foggy brain decide that a life of blurry vision is better than muddling through this mess of terminology, take a deep breath, and read on for complete visual and mental clarity.
The first step in discerning your prescription is to realize that oculus dexter (OD) and oculus sinister (OS) are simply the Latin terms for right and left eye. Oculus uterque (OU) merely refers to both eyes. Some doctors have opted to use RE for right eye and LE for left eye. In any case, your prescription will always be written with the right eye first. The reason for this is that your eye doctor examines your eyes from left to right as he or she would read text. This means that your right eye comes first as your doctor faces you.
Other Key Terminology
- Sphere (SPH) is an indication of the amount of lens power prescribed to correct your vision. It is measured in diopters (D). A plus sign means that you are farsighted while a minus sign indicates nearsightedness.
- Cylinder (CYL) describes the lens power required to treat astigmatism. An absence of this measurement means that you do not suffer from astigmatism. The plus and minus signs have the same meanings as with SPH.
- Axis refers to the lens meridian that does not have a cylinder power. This is used when no astigmatism is present. The axis ranges from 1 to 180. The number 90 aligns with the vertical meridian of your eye; 180 aligns horizontally.
- Add is simply the added magnifying power that must be added to the lower portion of a multifocal lens, which includes bifocals and trifocals. This type of lens is used to treat presbyopia. This measurement typically ranges from +0.75 to +3.00 D and is the same power for both eyes.
- Prism notates the amount of prismatic power needed to compensate for alignment problems.
It is important to note that eyeglass prescriptions are not the same as those written for contact lenses. Additional information and measurements are required to ensure the proper fit of a contact lens.
Your eyeglass prescription must be given to you upon completion of an eye exam and is yours to keep, thanks to the Federal Trade Commission’s law regarding the release of prescriptions. This allows you to fill your eyeglass prescription wherever you’d like.