Where should segment heights be measured when fitting a new pair of glasses?

Measuring segment heights on the actual frame that will be worn is crucial for ensuring the most accurate fit and optimal vision correction. Segment height refers to the distance from the bottom of the lens to the line of sight or the pupil, particularly for bifocal or progressive lenses. When this measurement is taken on the specific frame that the patient will be using, it accounts for the unique characteristics of that frame, such as its size, shape, and curvature.

If measurements were taken using tools like a pupilometer or based on previous eyewear or duplicates, they would not reflect the specific positioning of the lenses in the new frames. Each frame sits differently on the face and may affect how and where the lenses should be aligned with the patient's eyes. Therefore, using the actual frame ensures that the segment heights are precise, providing the wearer with the best visual experience possible.