Which of the following rigid lens overall diameters would be considered large?

• A. 8.6 mm
• B. 8.2 mm
• C. 9.0 mm
• D. 9.3 mm

Answer: (D)

At a glance, the overall diameter of a rigid lens tells you how much of the cornea and surrounding sclera it covers. A larger diameter means more peripheral coverage and typically more lens stability and less lid-driven movement, which can help with irregular corneas or difficult centration. Diameters around 8.0–8.6 mm are considered small to standard, while diameters around 9.0 mm and larger are regarded as large.

Of the diameters listed, 9.3 mm clearly falls into the large category, offering more extensive coverage than the smaller options. The 9.0 mm diameter sits near the threshold and is less clearly large, while 8.6 mm and 8.2 mm are not large.