Difference between revisions of Diopters

* ''diopter gap'' (or ''diopter difference''): absolute difference in diopters between the values of the two eyes

* ''diopter ratio'': ratio of the diopters in one eye over the other one (right eye / left eye)

For example,the following correction:

can be expressed as a 0.5 dpt gap in both SPH and CYL, a 1.5 ratio in SPH and a 0.75 ratio in CYL:

Note that the term ''diopter ratio'' is often used interchangeably for ''diopter gap''<ref>{{cite jake|https://endmyopia.org/the-diopter-ratio-trap-dont-favor-one-eye/|The Diopter Ratio Trap: Don’t Favor One Eye}}</ref>, for example when talking about reducing a correction while keeping the ''gap'' the same. This can also be expressed as a [[wikipedia:Percent difference|percentage difference]] between the two diopter values<ref>{{cite jake|https://endmyopia.org/reducing-diopter-ratio-diy-patching-solution-pro-topic/|Reducing Diopter Ratio: DIY Patching Solution (PRO TOPIC)}}</ref> (e.g. the <tt>0.5 dpt</tt> difference between the right and left eyes here is equivalent to <tt>0.5 dpt / |-1.5 dpt| = 0.33</tt> or 33%).

The general recommendation is that the diopter gap is constant across all lenses being used. However, some old EM articles show successful cases where differentials are equalized but normalized have a 0.25 D gap.<ref>https://endmyopia.org/progress-improving-centimeter-62-90/ and https://endmyopia.org/saras-journey-truth-long-term-vision-improvement-potential/</ref>

Confusingly, diopter gap is also sometimes used to refer to the [[spherical equivalent]] difference between [[differentials]] and [[normalized]].<ref>https://endmyopia.org/pro-topic-managing-your-maximum-diopter-gap/</ref>