An eye prescription is done to find out the strength of eyes and the measurements are expressed in the form of diopters.  Various other measurements determine the strength of the necessary corrective devices too. The eye prescription is needed for getting the eye glasses or contact lenses.

Knowing the terms in an Eyeglass Prescription

  • O.D. and O.S.: O.D. stands for oculus dexter and O.S. stands for oculus sinister. These abbreviations come from the Latin words which mean right eye and left eye respectively. Also, some prescriptions mightt just refer to your eyes as “right” and “left”. O.U. stands for oculus uterque, referring “both eyes.”
  • Sphere or SPH: This term tells whether you are nearsighted or farsighted and how much correction your eyes need. If the numbers are negative, you are nearsighted and a plus sign or no symbol before the number means you are farsighted
  • Cylinder or CYL: It represents astigmatism which represents degree of correction needed.
  • AXIS: Symbolized as “X” on the prescription, it represents the orientation of the astigmatism. This value could be between 0 and 180. The horizontal median of the eye is indicated by 180 and the vertical median is indicated by 90.
  • ADD: AN ADD is always a positive number and represents the additional power required for reading. This is seen in the lower section of a multifocal or progressive lens.
  • PRISM (p.d.) and Base: A prism diopters or “p.d.,” represents prescription for double vision or diplopia. The base section represents the direction of the prism. The values could be “up,” “down,” “in,” or “out,” depending on the direction the light needs to be refracted.

Prescription For Eye Glasses vs Prescription For Contact Lenses

It is important to note that contact lens prescriptions are different than eyeglass prescriptions. They need different information. The prescription is measured based on the distance is from the eye and while contact lenses are right on the eyeball, eyeglasses sit further out, which needs adjustment of the correction needed. So, a prescription for an eyeglass cannot be used to purchase contact lenses, and vice versa.

Also, an eyeglass prescription could be a Single Vision, Bi Focal, Trifocal or Progressive depending upon the eye condition of the patient. Eye prescription could also be done to correct eye issues with using computer/mobile screens.

Patients should always take eye prescriptions from a knowledgeable and skilled eye specialist and should visit them regularly to check for change in prescriptions if any.