What is Segment Height (SH)?
Segment height is the vertical measurement starting from the bottom of the lens to the center of the pupil. This measurement helps place the beginning of the progressive addition in a progressive lens or the top line of lined bifocals. This measurement is in millimeters and is unique to each person who wears these types of lenses. For Single Vision lenses, this measurement does not apply.
How to Measure Your Own Segment Height
Segment height does not always appear on a prescription but is easily measured at home.
- Make sure you have a ruler that has millimeter measurements. If for whatever reason you can’t get your hands on one, you can use a centimeter ruler as well and multiply your final value by 10.
- Put on your glasses.
- Find a well-lit mirror that shows your entire face. Stand 8 inches away from it.
- Starting from the bottom of the lens, not the bottom of the frame, align the ruler to the 0 mark keeping it straight and vertical.
- Stare straight ahead into the mirror and read off that lines with the center of your pupil. This is the segment height for the frames you are wearing.
- Repeat a couple of times to make sure you are getting an accurate measurement. Feel free to ask for help from a friend if you are having trouble doing this yourself.
Segment height is required for ordering progressive lenses. Depending on the frame and person, the Segment Height might differ slightly. This means that your SH can change if you get a new pair of frames, so don’t assume the number of your SH without measuring it first.
Measuring the SH for progressive lenses is slightly different then bifocals. For bifocals, you measure from the bottom of your lenses to the top of your bottom eyelid. However, Fuse Lenses doesn’t carry bifocals, only single vision and progressive lenses.
You don’t need a professional to help you measure it. You can do it yourself, or ask for help from a friend. Just make sure to measure it a couple of times to make sure you’re getting consistent measurements. And even if you are a little bit off, it will more than likely not affect you unless it is a large difference.
For any concerns or questions about Segment Height or anything else regarding RX Lenses, our customer service team at Fuse is here to help.