Difference between revisions of Vertex distance
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<math>D_C=1/(1/D-x)</math>, | <math>D_C=1/(1/D-x)</math>, | ||
where <math>D_C</math> is the corrected diopter number, <math>D</math> is the diopter strength of your lenses and <math>x</math> is the vertex distance in meters. It is important to note here that this equation is sensitive to minus signs of your diopter strength. | where <math>D_C</math> is the corrected (perceived) diopter number, <math>D</math> is the diopter strength of your lenses and <math>x</math> is the vertex distance in meters. It is important to note here that this equation is sensitive to minus signs of your diopter strength. | ||
Example for a vertex distance of 15mm (=0.015m): | Example for a vertex distance of 15mm (=0.015m): | ||
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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 [[Plus Lenses]] and '''decreases''' the strength of [[Minus Lenses]]. The effect is noticeable above 4.0 dpt and is mostly negligible for [[Low Myopia]]. | |||
==References== | ==References== | ||