For a first-time trifocal wearer, where should the seg height be measured from?

• A. 1 mm below lower pupil margin
• B. From the line of the lower eyelid margin
• C. At the center of the pupil
• D. 2 mm above the pupil margin

Answer: (A)

The seg height is set so the reading portion of the trifocal sits in the lower part of the pupil when you’re looking straight ahead. For a first-time trifocal wearer, measure from the lower edge of the pupil about 1 mm below it. This provides a consistent, repeatable reference that keeps the near-reading segment aligned with the visual axis without requiring excessive downward gaze or head tilt.

Measuring from the lower eyelid margin can vary with lid position and blinking, making alignment less reliable. Placing the segment at the center of the pupil would put the reading portion too high for typical viewing, while 2 mm above the pupil margin would position it too far into the upper portion of the lens, not matching the intended reading zone.