What is a PD?

Pupillary Distance, or PD, is the horizontal distance between your eyes. It is measured from the center of your right eye's pupil to the center of your left eye's pupil. (The pupil is the black circle that is centered in the middle of the colored portion of your eye). A PD is recorded in millimeters. Most adults have a pupillary distance of about 59-68 mm. A PD measurement allows laboratory technicians to accurately manufacture your lenses so that the optics of your eyeglasses are positioned in front of the center of your eyes.

Can my eye doctor measure my PD?

Yes, eye doctors and opticians can measure your PD. Many eye doctors typically will not provide you with your PD because measuring for a PD is usually not part of a routine examination. Typically, an optician will take your PD when you are ordering new eyeglasses. You can always ask your eye doctor or optician to provide you with a PD measurement. Occasionally, they will assist you, but often they would prefer not to provide this service. Many eye doctors and opticians derive a portion of their income off of the sale of eyeglasses. So, you can understand that they may not be enthusiastic about providing free measurements just so that you can shop elsewhere.

Do I need to be wearing my frame to determine my PD?

No, the distance between your pupils can be measured with or without your eyeglass frames. Most eye doctors and opticians prefer to measure a patient's PD without them wearing their frames.

Does my PD change with time?

Once a patient has experienced puberty and is a full grown adult, their PD typically will not change. While a person's body does experience many changes throughout adulthood, changes in skull shape causing horizontal relocation of one's eyes is rare. For this reason, PD is very consistent throughout an adult's life. Young children and teenagers will experience increases in PD as they grow because the distance between their eyes is increasing as their skull and head become larger.

My glasses prescription does not have a PD. How can I get it?

1. You can go to your local eye doctor or optician and offer to pay them for the service of providing you with a PD. It's always a good idea to call your eye doctor or optician first to see if they are willing to provide this service. Remember, they may not be eager to help you because doing so means you probably will not be purchasing eyewear from them.
2. You can have a friend measure your PD while you are wearing your current glasses:
   • Have your friend stand directly in front of you, about two feet away.
   • Shut your left eye (or cover the left lens of your eyeglasses with your left hand if you are unable to shut your left eye while leaving your right eye open. Be careful not to bump or shift your glasses while you are blocking your sight).
   • Using your right eye, stare straight ahead into your friend's left eye (your friend's left eye should be directly in front of your right eye.)
   • Have your friend use a NONPERMANENT MARKER to make a mark on the lens of your eyeglasses that corresponds to the center of your right eye's pupil.
   • Repeat this process for the left eye. (Shut or cover your right eye and using your left eye, look straight ahead into your friend's right eye. Have your friend mark where the center of your pupil is located on the lens of your eyeglasses. Again, be careful not to shift or move your glasses if you are using your hand to block the vision of your right eye)
   • Using a millimeter ruler measure the distance in between the two marks.
   • Repeat this process 3 times and take the average of all 3 measurements. This value is your PD. Be sure to properly clean your glasses in between and after all measurements.
   
   
3. You can have a friend measure your PD while you are not wearing glasses:
   • Have your friend stand directly in front of you, about 2 feet away.
   • Using your right eye, stare straight ahead into your friends left eye (your friend's left eye should be directly in front of your right eye).
   • Have your friend align a millimeter ruler so that the zero mark of the ruler lines up with the center of your right eye's pupil. (Your friend will find it useful to rest the ruler on the bridge of your nose and his/her hand on your check. This allows your friend to hold the ruler level and steady.)
   • After your friend has aligned the zero mark of the ruler with the center of your right eye, use your left eye to look straight ahead into your friend's right eye. Your friend may notice that both of your eyes may move slightly during this process. That is not abnormal. If both eyes do move slightly your friend may notice that the zero mark of the ruler may not be perfectly positioned over the center of the right eye's pupil. This is fine; do not move the ruler. Keep the ruler in the same location.
   • Next, have your friend determine what number on the millimeter ruler lines up with the center of your left pupil while you are looking straight ahead into his/her right eye.
   • Record this number. Repeat this entire process 3 times and take the average of all 3 measurements. This average value is you PD. Be sure to properly clean your glasses in between and after all measurements.
   
4. You can take your own PD if you are wearing glasses and looking in the mirror:
   • Stand directly in front of mirror, about 1 foot away. It is important that you look directly straight ahead. Looking in the mirror at an angle can skew the PD results.
   • If possible shut your left eye and leave your right eye open. (If you are unable to shut your left eye while leaving your right eye open, block your left eye by placing your left hand over your eyeglasses' left lens. Be careful not to bump or shift your glasses).
   • While looking straight ahead into the mirror, use a NONPERMANENT MARKER to make a mark on the right lens of your eyeglasses that corresponds to the center of your right eye's pupil. Be careful not to poke yourself in the eye or mark on yourself. This can be a little tricky since you will be watching the mirror image of yourself but applying the mark directly to the outside portion of the eyeglass lens you are wearing.
   • Repeat this process for the left eye (Close or cover your right eye during this process and be careful not to bump or shift your glasses. Using your left eye, look at the eye directly in front of you in the mirror. Make a mark that corresponds to the center of your left eye's pupil).
   • Remove your frame and using a millimeter ruler measure the distance in between the two marks. Repeat this entire process 3 times and average the 3 numbers. This is your PD. Be sure to properly clean your glasses in between and after all measurements.