# Difference between revisions of Diopters

(Define gap and ratio) |
(→Gap and ratio: Add references, mention common usage of "ratio" and add "diopter difference") |
||

Line 27: | Line 27: | ||

Comparisons between two diopters is typically expressed using one of these terms: | Comparisons between two diopters is typically expressed using one of these terms: | ||

− | * ''diopter gap'': absolute difference in diopters between the values of the two eyes | + | * ''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) | * ''diopter ratio'': ratio of the diopters in one eye over the other one (right eye / left eye) | ||

Line 41: | Line 41: | ||

(-1.5 dpt) / (-1.0 dpt) = 1.5 | (-1.5 dpt) / (-1.0 dpt) = 1.5 | ||

(-1.5 dpt) / (-2.0 dpt) = 0.75 | (-1.5 dpt) / (-2.0 dpt) = 0.75 | ||

+ | |||

+ | 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 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%). | ||

==References== | ==References== | ||

{{reflist}} | {{reflist}} | ||

[[Category:Articles]] | [[Category:Articles]] |

## Latest revision as of 16:54, 1 August 2020

Diopter is a measure of the power of a lens (or mirror) and is equal to the reciprocal of focal length in meters. The unit symbol for diopters is dpt, D, or m^{-1}.

- In EM we refer to the cm measurement to calculate diopters needed to correct refraction of the eye. If you can see 50cm clearly your diopters will be .

- Lenses in series add their powers : if you're wearing -2 diopter contacts (adjusted for glasses strength) and put +1 diopter reading glasses over the contacts you're in effect wearing -1 diopters.
- A lens with a negative diopter sign compensates for nearsightedness while a lens with a positive diopter sign compensates for farsightedness.

0.00 to -0.75 dpt | Probably don't need glasses |

-1.00 to -2.00 dpt | Mild myopia, no differentials needed |

-2.00 to -5.00 dpt | Moderate myopia, glasses always needed |

-5.00 to -10.00 dpt | High myopia |

-10.00+ dpt | Very high myopia. Field of view significantly reduced. |

## Gap and ratio

Comparisons between two diopters is typically expressed using one of these terms:

*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:

OD: -1.5 SPH / -1.5 CYL OS: -1.0 SPH / -2.0 CYL

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:

|(-1.5 dpt) - (-1.0 dpt)| = 0.5 dpt |(-1.5 dpt) - (-2.0 dpt)| = 0.5 dpt (-1.5 dpt) / (-1.0 dpt) = 1.5 (-1.5 dpt) / (-2.0 dpt) = 0.75

Note that the term *diopter ratio* is often used interchangeably for *diopter gap*^{[1]}, for example when talking about reducing a correction while keeping the *gap* the same. This can also be expressed as a percentage difference between the two diopter values^{[2]} (e.g. the `0.5 dpt` difference between the right and left eyes here is equivalent to `0.5 dpt / |-1.5 dpt| = 0.33` or 33%).

## References

- ↑ The EndMyopia Blog, https://endmyopia.org/the-diopter-ratio-trap-dont-favor-one-eye/
- ↑ The EndMyopia Blog, https://endmyopia.org/reducing-diopter-ratio-diy-patching-solution-pro-topic/