posted: Jan. 11, 2018.
Have you ever wondered what the PD measurement is??
The PD or pupillary distance is the distance measurement between the centers of your two eyes. It is measured in millimeters. This measurement is used to align the center of your eyes with the optical center of your glasses. Most people assume this is taken by your Optometrist during the eye examination. It is not part of the eye health examination. It is taken by the licensed optician to complete your order for new glasses or lenses. The licensed optician is highly trained to design, verify and fit eyeglass lenses and frames. They use the prescriptions supplied by the Optometrist in your eye examination. The optician uses a digital pupillometer to take your pd measurement. The pupillometer measures one eye at a time for your monocular pd. It also measures your near and distance pd. It is more accurate especially for high refractive errors or progressive lenses for precise centration. For multifocal lenses the two key measurements are the pd and seg height. The seg height is the vertical measurement in millimeters from the bottom of the lens in your frame to the beginning of the progessive addition on your lens. It needs to be measured when you have your frame on, that you are putting lenses in. So if your ordering glasses online how do they do this important measurement?? A seg height is only needed for multifocal lenses not single vision lenses. If your lenses are not aligned properly it can cause eyestrain, headaches, distorted vision, double vision and blurred vision.