What is Segment Height (SH)?
Segment Height, also known as Seg Height or SH, is the vertical measurement in millimeters from the bottom of the lens in your frames, to the beginning of the progressive addition on a progressive lens. Segment height does not apply to Single Vision lenses. The determined Segment Height is specific to each frame and wearer.
How do I measure my own Segment Height?
Follow these instructions to measure your own Segment Height at home:
1. Prepare a mirror, a standard ruler with the minimum unit of millimeter.
2. Put the glasses on your face and adjust them so that they sit comfortably.
3. Stand about 8 inches (20 cm) away from a well lit mirror with your face parallel and square to the mirror.
4. Align the ruler’s zero (0) measurement to the lowest point at the bottom of your left lens, keeping it exactly vertical.
Make sure you are measuring from the bottom of the clear lens, not the bottom of the frame (see graphic).
5. Stare straight ahead and read the millimeter mark inline with the center of your pupil. This is your segment height measurement for these frames.
6. Repeat these steps at least 3 to 5 times to get an accurate and consistent measurement. Make sure your head and the ruler do not move after lining up the zero (0) measurement with the bottom of your left lens until you note your measurement. Ask a friend to help if you are having trouble.