Certified Paraoptometric (CPO) Practice Exam 2026

CR-39 lenses are a type of plastic lens known for their lightweight properties and impact resistance, which make them advantageous for eyewear. A notable characteristic of CR-39 lenses compared to glass lenses is their significant reduction in weight. CR-39, being a plastic material, is much lighter than glass, which makes eyewear more comfortable for prolonged use and can also reduce the overall bulk of the frames.

While glass lenses may provide superior optical clarity and scratch resistance, the weight of glass often leads to discomfort, especially in high prescriptions. The lighter nature of CR-39 lenses allows for thinner, more aesthetic designs that are easier to wear. Additionally, CR-39 lenses are less likely to shatter upon impact, contributing to their popularity in safety glasses and everyday eyewear as an alternative to glass.

Thicker than glass is inaccurate, as CR-39 can be manufactured to be thinner than glass lenses while still maintaining high refractive capabilities. The misconception around scratch resistance may lead some to feel that CR-39 is less durable, but this does not define its primary benefit as much as its lightweight and flexible nature does. Thus, the correct acknowledgment of CR-39 lenses emphasizes their lightweight advantage in comparison to glass lenses.