The overwhelming majority people have a credit card or driver’s license. Even a gift card will do the trick. These cards are all 85.6 mm wide. By taking a picture with a credit card held up to the forehead, we can easily measure the distance between a patient’s pupils and get them a pair of glasses lined up to their pupils. We can also use the credit card to determine seg heights when a patient is wearing a frame.

A special thanks to fellow optical nerd Dr. Irene Yang for pointing out this helpful tip: If the patient is looking at the phone for the picture, their eyes will converge slightly. When taking this picture, instruct the patient look into the distance while snapping the photo. This can lead to a difference of 1 or 2 millimeters in the PD measurement.

We are working on finding an application to do this without transmitting photographs, but for the time being, if you send a photo to us at Chadwick Optical, we’ll reply with the PD number. If you have any questions, let us know. Also, here’s a link to a video on how to measure the PD using a picture in Photoshop.