Optics of low-vision magnifiers

This article discusses the determination of magnification needs for reading in low vision patients.

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Abstract

Magnifiers are commonly prescribed for low-vision patients. This article discusses the determination of magnification needs for reading, it warns against relying on the labelled magnification and it advocates using equivalent viewing distance (EVD) to quantify magnification effects. Spectacle magnifiers, hand-held magnifiers, stand magnifiers, telescope systems and electronic magnifiers are discussed. The most important optical parameters are identified and methods are given for determining the EVD and the field of view these magnifiers provide. There are simple methods for determining equivalent powers of lenses and the image locations and enlargement ratios of stand magnifiers.

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