Certified Paraoptometric (CPO) Practice Exam 2025

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What is the term used to designate a lens that has no optical power?

Plus lens
Minus lens
Plano
Spherical

The correct answer is: Plano

The correct term used to designate a lens that has no optical power is "plano." A plano lens has a surface that is flat, which means it does not converge or diverge light. This makes it optically neutral, unlike lenses with positive or negative power, which are designed to either converge light rays (plus lenses) or diverge them (minus lenses). Additionally, the term "spherical" refers to the shape of the lens surface but does not imply that it has no optical power. Thus, "plano" accurately describes a lens that has no effect on the direction of light and is essential for specific applications in optics where neutralization of power is required.