Decentration refers to which of the following?

• A. The distance between the two eyes
• B. The horizontal displacement of the lens optical center from the frame
• C. The thickness of the lens
• D. The vertex distance

Answer: (B)

Decentration is about how the lens’s optical center sits relative to the frame and the wearer’s eye. When the optical center is shifted horizontally from the frame, light no longer passes straight through the center of the lens as intended, creating unwanted prismatic effects and potential visual discomfort. The choice that describes this horizontal displacement of the lens optical center from the frame matches what decentration means. The other terms refer to different concepts: interpupillary distance is the distance between the pupils, lens thickness is just how thick the lens is, and vertex distance is the gap between the cornea and the back surface of the spectacle lens.