Brief Answer:
Unit of measurement of refractive power of lens.

Detailed Answer:
Hello XXXX
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Diopter is a unit of measurement of the refractive power of lenses or curved mirror and it is equal to the reciprocal of the focal length measured in meters.
A Diopter is a number which tells the power or focal length of a lens or mirror.

In other words,it is a unit for expressing the focusing or diverging strength of a lens or mirror and it is the reciprocal of the focal length measured in metres, for a diverging optical element it is expressed as a negative value and for a converging one it is expressed as a positive value.
This in turn can tell the farthest distance we can focus through the lens or mirror.

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Dr.Indu XXXXXXX

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