Difference between revisions of Diopters
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(Added unit symbols, added some math formatting, cleared up some confusing range formatting.) |
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{{Under_construction}} | {{Under_construction}} | ||
Diopter is a measure of the power of a [[lens]] (or mirror) | 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<sup>-1</sup>. | ||
<math>D = \frac{1}{f}</math> | |||
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 <math>\frac{1}{0.50}=2dpt</math>. | |||
Lenses in series add their powers : if you're wearing -2 diopter contacts ([[vertex distance|adjusted for glasses strength]]) and put +1 diopter reading glasses over the contacts you're in effect wearing -1 diopters. | Lenses in series add their powers : if you're wearing -2 diopter contacts ([[vertex distance|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]]. | A lens with a negative diopter sign compensates for [[nearsightedness]] while a lens with a positive diopter sign compensates for [[farsightedness]]. | ||
Approximate categorizations of myopia by [[spherical]] lens power: | {| class="wikitable" | ||
|+ Approximate categorizations of myopia by [[spherical]] lens power: | |||
0.00 | |- | ||
| 0.00 to -0.75 dpt || Probably don't need glasses | |||
-1.00 | |- | ||
| -1.00 to -2.00 dpt || Mild myopia, no [[differentials]] needed | |||
-2.00 | |- | ||
| -2.00 to -5.00 dpt || Moderate myopia, glasses always needed | |||
-5.00 | |- | ||
| -5.00 to -10.00 dpt || High myopia | |||
-10.00+ | |- | ||
| -10.00+ dpt || Very high myopia. Field of view significantly reduced. | |||
|} | |||
==References== | ==References== | ||
{{reflist}} | {{reflist}} | ||
[[Category:Articles]] | [[Category:Articles]] |
Revision as of 17:16, 9 June 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. |