Difference between revisions of Measurement

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m (→‎cm Measurement: make everything into steps!)
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== cm Measurement ==
 
== cm Measurement ==
A simple test for your level of myopia is to hold a ruler up to your eye, and measure how far away you can still read text without [[blur]].  If you measure this distance in centimetres, this is your "cm measurement". The ideal precise measurement is from the surface of your eyeball, but this is obviously not safe, so measure from some facial structure near your eye. Consistency is more important than accuracy, you want to be able to track your small changes over the course of a day, and larger changes over time.
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The cm measurement uses a basic optics formula to calculate the diopters of correction you need to see clearly long distance. 
 
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# Hold a ruler up to your eye, and measure how far away you can still read text without [[blur]] in centimetersThis is your "cm measurement".
[[Diopters]] = -100cm/cm measurement.
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#* The ideal precise measurement is from the surface of your eyeball, but this is obviously not safe, so measure from some facial structure near your eye.
 
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#* Consistency is more important than accuracy, you want to be able to track your small changes over the course of a day, and larger changes over time.
This test is fairly accurate up to about -10 Diopters.  This is not corrected for [[vertex distance]], but below -4D vertex distance has no significant effect, and your [[normalized]] lenses should be a little low anyway.
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# Calculate diopters from the measurement: [[Diopters]] = -100cm/cm measurement.
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# If your result is stronger than -4D, and you wear glasses, you'll need to correct for [[vertex distance]] to convert this from contacts diopters to glasses diopters.
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# If your result is stronger than -10, you'll likely have problems getting consistent readings.
  
 
== Trial Refraction ==
 
== Trial Refraction ==

Revision as of 00:18, 6 September 2020


cm Measurement

The cm measurement uses a basic optics formula to calculate the diopters of correction you need to see clearly long distance.

  1. Hold a ruler up to your eye, and measure how far away you can still read text without blur in centimeters. This is your "cm measurement".
    • The ideal precise measurement is from the surface of your eyeball, but this is obviously not safe, so measure from some facial structure near your eye.
    • Consistency is more important than accuracy, you want to be able to track your small changes over the course of a day, and larger changes over time.
  2. Calculate diopters from the measurement: Diopters = -100cm/cm measurement.
  3. If your result is stronger than -4D, and you wear glasses, you'll need to correct for vertex distance to convert this from contacts diopters to glasses diopters.
  4. If your result is stronger than -10, you'll likely have problems getting consistent readings.

Trial Refraction

If your vision is worse than -10D, you may need a trial lens kit to measure your own myopia, or you may just stick to professional optometrist exams.

Tools

References