Difference between revisions of Vertex distance
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sentence case.
Viceroy Sam (talk | contribs) (update link) |
Viceroy Sam (talk | contribs) (sentence case.) |
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<math>-4.0 dpt: D_C=1/(1/(-4.0)-0.015)=-3.774 dpt</math> | <math>-4.0 dpt: D_C=1/(1/(-4.0)-0.015)=-3.774 dpt</math> | ||
In the above example the -4.0 dpt glasses yield the same level of correction as -3.75 dpt contact lenses. It can be seen that vertex distance '''increases''' the strength of [[ | In the above example the -4.0 dpt glasses yield the same level of correction as -3.75 dpt contact lenses. It can be seen that vertex distance '''increases''' the strength of [[plus Lenses]] and '''decreases''' the strength of [[minus lenses]]. The effect is noticeable above 4.0 dpt and is mostly negligible for [[low myopia]]. | ||
The expression looks less intimidating when you remember that (by definition) the [[ | The expression looks less intimidating when you remember that (by definition) the [[diopter]] is the reciprocal of the focal length. So it's really just: | ||
<math>f_C = f - x</math> | <math>f_C = f - x</math> | ||
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If you wore contact lenses before EndMyopia (EM) and continue to use contact lenses throughout your EM journey - Then vertex distance doesn't affect you. | If you wore contact lenses before EndMyopia (EM) and continue to use contact lenses throughout your EM journey - Then vertex distance doesn't affect you. | ||
If you wore glasses before EM and continue to wear glasses during EM then it is recommended to invest in a [[ | If you wore glasses before EM and continue to wear glasses during EM then it is recommended to invest in a [[lens kit]] and choose your reduced lenses based on testing your visual acuity - Then vertex distance doesn't affect you. If you do not have access to a lens kit and you want to reduce in pre-defined diopter steps - Then vertex distance can affect you: For example, reducing from -14.0 dpt to -13.75 dpt at a vertex distance of 15mm results in an effective perceived diopter drop of only 0.17 dpt, further reducing to -13.5 dpt would result in an effective diopter drop of 0.34 dpt. | ||
If you switch from glasses to contact lenses at high myopia or vice-versa you definitely will need to account for vertex distance before buying new corrections. | If you switch from glasses to contact lenses at high myopia or vice-versa you definitely will need to account for vertex distance before buying new corrections. | ||
* <div> '''I wear contact lenses as [[normalized]] and put [[ | * <div> '''I wear contact lenses as [[normalized]] and put [[plus lenses]] over them as my [[differentials]]. Do I need to worry about vertex distance?'''</div> | ||
No. Your differential correction will not undercorrect you by a diopter margin where vertex distance plays a role. | No. Your differential correction will not undercorrect you by a diopter margin where vertex distance plays a role. | ||