American Board of Opticianry (ABO) Practice Test 2025 - Free ABO Practice Questions and Study Guide

The measurement that refers to the height at which the optical center of the lens sits is known as seg height. This measurement is crucial, especially in bifocal and progressive lenses, as it determines the proper placement of the lens segments to ensure that the user can see through the optical center. For bifocal lenses, the seg height is the distance from the bottom of the lens to the area where the reading portion begins, while for progressive lenses, it is measured to provide the most comfortable and effective vision across different distances. Proper seg height ensures that the optical center aligns with the wearer's line of sight, which is essential for optimal visual performance and comfort.

Other terms like frame width refer to the overall width of the eyewear frames, pupil distance measures the distance between the centers of the pupils, and vertex distance is the distance between the back surface of the lens and the front of the eye. These measurements are important for fitting and optics but do not specifically address the height of the optical center in relation to the lens.