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

To make your perfect pair of TheraSpecs, every multifocal prescription needs a segment height: the number that marks where your Rx strength changes.

If you're using one of our frames, you have the choice of:

• 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 not 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.

If you're sending in your own pair of glasses to fit with prescription lenses, then be sure to send them with:

(1) a known segment height, a request for a default segment height, or with (2) multifocal lenses inside of the frames.