What does ED refer to in the context of eyewear measurements?

In the context of eyewear measurements, ED refers to "Effective Diameter." This term is critical in the design and fitting of eyeglass lenses, as it represents the largest diameter of the lens, which is essential for determining the appropriate prescription and fit for the wearer. The effective diameter helps opticians assess how much of the lens will be visible to the wearer and ensures that the optical center aligns correctly with the pupil. By considering the effective diameter, opticians can make better decisions regarding frame selection, lens type, and even consider factors related to lens curvature and design, which can affect visual clarity and comfort.

The other terms, while they might sound related, do not accurately reflect the context of eyewear measurements. Eye diameter, edge distance, and eye distance refer to different concepts and measurements that are not used as standard terms in lens fitting and design decisions.