Which statement is true about the index of refraction among crown glass, CR-39, Polycarbonate, and Trivex?

• A. CR-39 has the lowest index
• B. Crown glass has the lowest index
• C. Polycarbonate has the lowest index
• D. Trivex has the lowest index

Answer: (A)

Light slowing and bending in a lens material is determined by its index of refraction. Among these common ophthalmic materials, CR-39 has the smallest index, about 1.498. Crown glass sits a bit higher (roughly 1.52), Trivex is around 1.532, and polycarbonate is the highest (about 1.586). So CR-39 truly has the lowest index, which is why that statement is the correct one.