Most frames are designed to hold lenses with what power base curve?

• A. 6 D
• B. 4 D
• C. 2 D
• D. 8 D

Answer: (A)

Frames are built to accommodate a standard back-surface curvature of the lenses, known as the base curve. A base curve of about 6 diopters is the typical default used in most frames. This curvature provides a good balance between frame fit, edge thickness, and ease of mounting across a wide range of prescriptions. In practical terms, 6D corresponds to a moderate curve that lets lenses seat well in the rim without creating excessive edge thickness or fit issues. Using a much flatter base curve (like 2D or 4D) can leave gaps or alter fit, while a much steeper curve (like 8D) can cause seating problems and thicker edges.