For measuring bifocal seg height, the reference line is drawn at which landmark?

• A. At the level of the lower eyelid margin
• B. At the pupil center
• C. 2 mm below the lower eyelid margin
• D. 1 mm below the lower lid margin

Answer: (A)

Measuring bifocal seg height relies on a stable, external landmark to place the reading segment consistently. The lower eyelid margin serves that role, so a horizontal reference line is drawn right at its level. This keeps the top edge of the bifocal segment aligned with the wearer’s natural reading position as they look down, providing standardization across patients. The pupil center is internal and changes with gaze, so it wouldn’t be a reliable reference. Fixed offsets below the lid margin don’t provide the same consistent baseline, which is why the level of the lower eyelid margin is the best choice.