Approximately 2.2 mm thickness is most likely which material?

• A. Glass
• B. CR-39
• C. Polycarbonate
• D. Trivex

Answer: (A)

Lens thickness for a given prescription is largely determined by refractive index: higher index plastics bend light more efficiently, so you can achieve the same dioptric power with less material, yielding thinner lenses. Conversely, lower index materials require more material to reach the same power, leading to thicker lenses, especially at the edges. Among the listed materials, high‑index plastics like polycarbonate and Trivex tend to produce thinner lenses than CR-39 or glass for the same prescription. Glass, while sharing a modest index similar to CR-39, is heavy and less amenable to thinning in practice, so edge thickness often ends up around 2 mm or more for typical prescriptions. Therefore, an approximate thickness of 2.2 mm is most consistent with glass.