What is segment height, and why is it required for a bifocal or progressive pair of TheraSpecs?

Every bifocal or progressive  prescription needs a measurement called a segment height, which marks where you prescription strength changes.

TheraSpecs Frames

If you're using one of our frames, we'll email you after your order is place to ask to choose between:

• Using a default segment height. Defaults are based on the lens height and most common segment heights for that frame. The default works for most people, but is not right for everyone.
• Having us ship you a trial pair shortly after you place your order to have your optometrist measure your segment height in that frame. Be sure to let them know whether you need the measurement for lined bifocals or progressive lenses. This will take a little more time, but is the most accurate measurement.

If we don't hear back from you in response to that email, we'll make your lenses with the default segment height.

Your Own Frame

If you're sending in your own pair of glasses to fit with prescription lenses, then be sure to send them with either a known segment height, a request for a default segment height, or with bifocal or progressive lenses inside the frame.