If there is BU over one eye, how should you adjust the seg height?

• A. Raise seg height
• B. Lower seg height
• C. Maintain seg height
• D. Increase seg height by 0.5 mm

Answer: (B)

Base Up prism over one eye shifts the image upward in that eye. To keep the near portion of the lens aligned with the pupil during reading, you lower the segment height on that eye. Lowering the seg height moves the reading area downward on the lens so the wearer looks through the correct portion when glancing down. Raising the segment would worsen the misalignment, and keeping it the same wouldn’t compensate for the BU shift. A fixed 0.5 mm increase isn’t appropriate without specific measurement, since the needed correction depends on the amount of BU prism and how the wearer uses the lenses.