Difference between revisions of Diopters

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| -10.00+ dpt || Very high myopia. Field of view significantly reduced.
 
| -10.00+ dpt || Very high myopia. Field of view significantly reduced.
 
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==Gap and ratio==
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 +
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 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
 +
 
==References==
 
==References==
 
{{reflist}}
 
{{reflist}}
 
[[Category:Articles]]
 
[[Category:Articles]]

Revision as of 16:59, 30 July 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.
Approximate categorizations of myopia by spherical lens power:
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: 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

References