What term describes the adjustment made to avoid induced prism when fitting frames?

What term describes the adjustment made to avoid induced prism when fitting frames?

• A. Vertex distance
• B. Decentration
• C. Prismatic correction
• D. Frame height

Answer: (B)

The idea is to place the lens centers where the eye naturally looks, so light passes through the optical center rather than through off-center areas. Induced prism happens when you view through a lens away from its optical center, which shifts the image and can cause eye strain or double vision. The way to prevent this during frame fitting is decentration—shifting the lenses horizontally (and vertically if needed) so the optical centers align with the wearer's pupils in primary gaze. This alignment keeps the light path straight through the lens and avoids unwanted prism. Vertex distance is about how far the lens sits from the eye, which can influence overall power and prism in some cases but is not the adjustment used to prevent induced prism by frame fit. Frame height concerns the vertical position of the frame and does not control prism. Prismatic correction involves adding prescribed prism to the lenses to address eye alignment, not the process of aligning the lenses within the frame to avoid prism.

The idea is to place the lens centers where the eye naturally looks, so light passes through the optical center rather than through off-center areas. Induced prism happens when you view through a lens away from its optical center, which shifts the image and can cause eye strain or double vision. The way to prevent this during frame fitting is decentration—shifting the lenses horizontally (and vertically if needed) so the optical centers align with the wearer's pupils in primary gaze. This alignment keeps the light path straight through the lens and avoids unwanted prism.

Vertex distance is about how far the lens sits from the eye, which can influence overall power and prism in some cases but is not the adjustment used to prevent induced prism by frame fit. Frame height concerns the vertical position of the frame and does not control prism. Prismatic correction involves adding prescribed prism to the lenses to address eye alignment, not the process of aligning the lenses within the frame to avoid prism.