Breaking down everything you need to know so you can order with confidence.


Here are some common abbreviations and what they stand for:

OS or Oscular Sinister: Right Eye.

OD or Oscular Dextrus: Left Eye.

“Plus” Symbol (+): This symbol in front of the number means you are farsighted.

“Minus” Symbol (-): This symbol in front of your number means you are nearsighted.

“D” or Diopter: This unit is used to measure the correction or focusing power of the lens your eye requires. For example, if your prescription says -1.00, you have one diopter of nearsightedness. Similarly, +1.00 would be a small amount of farsightedness.



PD or Pupillary Distance: The distance between the center of each pupil. Measured in milimeters (mm). The average adult PD range is between 54-74 mm.

Dual PD: A dual PD is provided with two numbers and represents the measurement of each pupil center to the center of the bridge of your nose in millimeters.

If you don’t have a PD on your prescription, you can measure it yourself using our guide below.

Got Astigmatism?

For people who have astigmatism, there will be three numbers in your prescription. The general form for writing these numbers is S (Sphere) x C (Cyclinder) x Axis.

Sphere (S): the “spherical” portion of the prescription, which is the degree of nearsightedness or farsightedness

Cylinder (C): The unit that measures in diopters the degree of astigmatism that you have. Can be a negative or a positive number.

Axis: Between 0 and 180 degrees, determines the orientation of the astigmatism.

Together, a person with astigmatism may have a prescription that looks like this:

OS: -2.50 +150 x 180

OD: +3.00 +3.00 x 40


Your eye doctor will usually measure your PD during an eye exam, but you can also measure it at home! Follow the steps below to 

Grab a ruler (preferably one you can easily convert into millimeters).



Stand 8 inches in front of a mirror and hold the ruler against your brow a mirror and hold it against your eyebrows.


Close your right eye and align the 0 millimeter mark to the center of your left pupil.


Look straight ahead and then close your left eye and open the right eye.


The millimeter line that lines up to the center of your right pupil is your PD. 

Measure your PD 3-4 times to ensure it’s accurate! Keep in mind that the range of Adult PD: 54-74 mm. 

SINGLE PD is the pupillary distance between the center of one pupil to the other, which can be a distance PD or near PD. Distance PD can be used to order any type of prescription glasses except reading glasses. Read below to learn how to calculate near PD for reading glasses.

DUAL PD, or monocular PD, consists of two numbers and is the distance between the centers of each pupil to the bridge of the nose. Dual PD is usually written in the following notation: 32/30. The first number is always the right eye (OD) measurement, and the second number is the left eye (OS).


We understand that it can be confusing if this is your first time ordering prescription glasses online. Contact us and we can help you out! 

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