Which thickness range is CR-39 typically associated with?

• A. 1.9-2.2 mm
• B. 1-2 mm
• C. 2-3 mm
• D. >3 mm

Answer: (A)

CR-39 is the standard plastic used for many spectacle lenses because it is lightweight and easy to fabricate, with good optical quality. For a typical eyeglass prescription and standard frame, the center thickness of a CR-39 lens sits around about 2 mm. The range 1.9–2.2 mm reflects this common, mid-range thickness you’d expect in everyday CR-39 lenses.

If the prescription is very strong or the frame is large, the lens ends up thicker (often in the 2–3 mm range or more), so those options represent thicker lenses rather than the typical baseline. A thickness near 1–2 mm would be thinner than usual for most standard prescriptions, and >3 mm is generally for high-power cases or specialty lenses.