Difference between revisions of Diopters
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Diopter is a measure of the [ https://en.wikipedia.org/wiki/Optical_power optical power ] P of a [[ lens ]] (or mirror) and is equal to the reciprocal of the [[ focal length ]] in meters . The most common unit symbol for diopters is dpt, D, or m <sup> - 1 </sup> . | Diopter is a measure of the [https://en.wikipedia.org/wiki/Optical_power optical power] P of a [[ lens ]] (or mirror) and is equal to the reciprocal of the [[ focal length ]] in meters . The most common unit symbol for diopters is dpt, D, or m <sup> - 1 </sup> . | ||
<math>P = \frac{1}{f} = - \frac{1}{d}</math> | <math>P = \frac{1}{f} = - \frac{1}{d}</math> | ||
* In [[ EM ]] , we use the [[ cm measurement ]] to calculate the diopters needed to correct [[ refraction]] of the eye. If you can see clearly at 50cm, your diopters will be <math> - \frac{1}{0.50}= - 2 dpt</math> . | * In [[ EM ]] , we use the [[ cm measurement ]] to calculate the diopters needed to correct [[ refraction]] of the eye. If you can see clearly at 50cm, your diopters will be <math> - \frac{1}{0.50}= - 2 dpt</math> OR <math> - \frac{100}{50}= - 2 dpt</math>. | ||
* Serial lenses add their powers: if you wear - 2 diopter contact lenses ( [[ vertex distance | adjusted for glasses strength ]] ) and put on reading glasses +1 diopter on the lenses you actually wear - 1 diopter. | * Serial lenses add their powers: if you wear - 2 diopter contact lenses ( [[ vertex distance | adjusted for glasses strength ]] ) and put on reading glasses +1 diopter on the lenses you actually wear - 1 diopter. | ||
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== Gap and ratio == | |||
Comparisons between two diopters are usually expressed using one of these terms: | Comparisons between two diopters are usually expressed using one of these terms: | ||
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, for example when talking about reducing a correction while keeping the same '' gap '' . This can also be expressed as a [[ wikipedia: Percent Difference | percentage difference ]] between the two diopter values <ref> {{ quote jake | https://endmyopia.org/reducing - diopter - ratio - diy - patching - solution - pro - topic/ | Diopter Ratio Reduction: DIY Solution (PRO TOPIC) }} </ref> (for example, the <tt> 0.5 dpt </tt> difference between the right eye and the left eye is here equivalent to <tt> 0.5 dpt / | - 1.5 dpt | = 0.33 </tt> or 33%). The general recommendation is that the left - | , for example when talking about reducing a correction while keeping the same '' gap '' . This can also be expressed as a [[ wikipedia: Percent Difference | percentage difference ]] between the two diopter values <ref> {{ quote jake | https://endmyopia.org/reducing - diopter - ratio - diy - patching - solution - pro - topic/ | Diopter Ratio Reduction: DIY Solution (PRO TOPIC) }} </ref> (for example, the <tt> 0.5 dpt </tt> difference between the right eye and the left eye is here equivalent to <tt> 0.5 dpt / | - 1.5 dpt | = 0.33 </tt> or 33%). The general recommendation is that the left - | ||
diopter differenceshould be constant on all lenses used. However, some old EM papers show successful cases where the differentials are equalized but normalized with a deviation of 0.25 D.<ref>https://endmyopia.org/progress- | diopter differenceshould be constant on all lenses used. However, some old EM papers show successful cases where the differentials are equalized but normalized with a deviation of 0.25 D.<ref>[https://endmyopia.org/progress-improving-centimeter-62-90/ Sara: Improving Centimeter from 62 to 90]</ref><ref>[https://endmyopia.org/saras-journey-truth-long-term-vision-improvement-potential/ Sara’s Journey: The Truth About Long Term Vision Improvement Potential]</ref> | ||
Confusingly, diopter deviation is also sometimes used to refer to diff - norm deviation, the difference between [[ differentials ]] and [[ normalized ]] or the [[ spherical equivalent ]] of this difference. <ref> | Confusingly, diopter deviation is also sometimes used to refer to diff - norm deviation, the difference between [[ differentials ]] and [[ normalized ]] or the [[ spherical equivalent ]] of this difference. <ref>[https://endmyopia.org/pro-qa-equalize-differentials-first/ Pro Q&A: Should You Equalize Your Differentials First?]</ref> | ||
It is often useful to disambiguate what is being compared: | It is often useful to disambiguate what is being compared: | ||
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** For example, if the norm is - 2 SPH - 0.5 CYL and the differentials are - 0.75 SPH, the diff - standard deviation is 1.25 SPH 0.5 CYL or 1.5 SPH equivalent. | ** For example, if the norm is - 2 SPH - 0.5 CYL and the differentials are - 0.75 SPH, the diff - standard deviation is 1.25 SPH 0.5 CYL or 1.5 SPH equivalent. | ||
** The axis is ignored. | ** The axis is ignored. | ||
** This quantity is usually positive, because more positive sphere is needed for [[ close-up ]] than for [[ distance vision ]] . | ** This quantity is usually positive, because more positive sphere is needed for [[ close-up ]] than for [[ distance vision ]] . | ||
==Technical Details== | ==Technical Details== | ||
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* http://billauer.co.il/simulator.html | * http://billauer.co.il/simulator.html | ||
=== Decentration === | |||
The Induced prism can be calculated using Prentice reign. Similar to Vertex Distance, shift is less of an issue for lower power lenses. | |||
The amount of prism power P induced by the decentration c of a lens of power f is <math>P=cf</math> 1 prism diopter displaces 1 cm for an object 1 m away. If c is in cm and f in diopters, then P is in prismatic diopters. A prism with vertex angle a and refractive index n gives an angle of light deflection d, which is equal to P diopters of the prism: <math>d=(n - 1)a</math> <math >P=100\tan{d}=100\tan((n - 1)a)</math> | The amount of prism power P induced by the decentration c of a lens of power f is <math>P=cf</math> 1 prism diopter displaces 1 cm for an object 1 m away. If c is in cm and f in diopters, then P is in prismatic diopters. A prism with vertex angle a and refractive index n gives an angle of light deflection d, which is equal to P diopters of the prism: <math>d=(n - 1)a</math> <math >P=100\tan{d}=100\tan((n - 1)a)</math> | ||
See [[Vertex distance#Calculation|Vertex distance -> Calculation]] | |||
== References == | |||
{{ reflist }} | {{ reflist }} | ||
[[ Category: Article ]] | [[ Category: Article ]] | ||