Explanation of words on optometry prescription:

    SVD - Single vision distance

    SVN - Single vision near

    OD - Right eye

    OS - Left eye

    OU - Both eyes

    Sphere - Nearsighted or farsighted

    Cylinder - Astigmatism

    Axs, or Axis - Orientation of Astigmatism

    ADD - presbyopia

    PD - Pupillary Distance (distance between your eyes)

Sphere determines nearsighted or farsighted

Cylinder is degree of astigmatism (This number may be all negative or a positive)

AXS or Axis is refers to the angle of correction for the astigmatism in the eye (the number between 1 and 180 degrees). If there is no Cylinder value or the value is 0, the Axis value must be 0 too.

Here is an example of a prescription with astigmatism in nearsighted and farsighted format：

    -2.00 -1.50 x 180

    +1.00 -0.50 x 068

If there is no astigmatism, you often see the prescription is as the following:

    -2.00

    +1.00

ADD refers to the degree of presbyopia (presbyopia caused by aging, this commonly begins to develop as age reaching to 40). For people who have no nearsightedness, farsightedness or astigmatism at all (usually do not need to wear eyeglasses), just fill in the degree of presbyopia at the ADD column. If you don't have the ADD power, please ignore the ADD column. 

For people who usually need to wear eyeglasses with presbyopia, there are two options to order the eyeglasses:

1. It can be equipped with a pair of eyeglasses for distance use, which can be worn when driving or walking, and another pair  of eyeglasses for reading book or computer.

2. If you don't want to carry 2 pair of different eyeglasses to replace frequently, you can configure the eyeglasses with bifocal or progressive lenses (same lens with the functions of distance and presbyopia).

Regardless of the method (1) or (2) above, the ADD data must be filled in. 

Here is an example of the prescription with ADD power：

    -2.00 -1.50 x 180

    +1.00 -0.50 x 068

    ADD +1.75 (Usually the right eye OD and left eye OS of this number are the same)

PD (Pupil Distance or Dist PD) refers to the distance between the two pupils. The average of pupil distance is between 53 millimeters (mm) to 70 millimeters (mm) for adult, and between 41 millimeters (mm) to 55 millimeters (mm) for children. Sometimes ophthalmologist or optometrist does not give this number. Please do not forget to request the PD measurement, and write it on the prescription. It is very important to have PD Measurement when ordering your eyeglasses on line!