What cranial positioning line should be perpendicular to the IR when positioning the patient for a lateral view of the facial bones?

• A. Interpupillary line (IPL)
• B. Frankfort horizontal
• C. Orbital line
• D. Midsagittal plane

Answer: (A)

Positioning a lateral view of the facial bones relies on a true side view with no rotation or tilt. The interpupillary line is a stable, easily identifiable reference that indicates whether the head is rotated. When you orient the patient so that the interpupillary line sits perpendicular to the image receptor, the skull lies in a true lateral position, ensuring symmetrical superimposition of the cranial structures and minimizing distortion of the facial bones. Other lines can be used for different baselines or views, but the interpupillary line provides the most reliable check to lock in the correct lateral orientation.