Diopter ratio question

What is more important in practical terms…the actual diopter ratio between the right and left eyeglass lenses (e.g. 1 : 0.9375), or the diopter difference between them (e.g. 0.25D)?

The actual ratio will never be the same for both differentials and normalized, since only 0.25 D increments are used. You’d need custom free form lenses in order to get them equal.

The diopter difference though, can be made equal easily.

Which one are we referring to when we casually talk about equal diopter ratios? The diopter difference, right?

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Exactly :wink:. That’s the one that’s spoken of in EM.


Yeaaaa… actually, a +1 from me for defining terms and trying to avoid un-mathematical terminology.

By mathematical definitions, the diopter ratio is not the diopter difference, and would be zero or undefined if one eye is plano. I’m in favor of saying diopter difference. It is easy to understand even for someone who is used to another term.