Certified Paraoptometric (CPO) Practice Exam 2025

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What does "ED" stand for in lens measurements?

Eye diameter
Effective diameter
Edge displacement
Entire diameter

The correct answer is: Effective diameter

The term "ED" in lens measurements stands for "Effective Diameter." This measurement is crucial as it reflects the diameter of the lens that is effective for optical purposes and fitting into frames. Understanding the effective diameter helps in determining how the lens will perform optically when placed in a frame, ensuring appropriate fitting and alignment with the wearer's requirements. The other terms, while they may seem related, do not accurately capture the definition used in optical measurements. "Eye diameter" pertains to a different anatomical measurement, "edge displacement" does not directly relate to lens sizing in the context of fitting and optics, and "entire diameter" is a somewhat vague term that does not specifically refer to the measurements used in the optical lens industry. Thus, "Effective Diameter" is the correct interpretation in the context of lens measurements.