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. 2019 Nov 8;21(11):e14808. doi: 10.2196/14808

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©Robert P L Wisse, Marc B Muijzer, Francesco Cassano, Daniel A Godefrooij, Yves F D M Prevoo, Nienke Soeters. Originally published in the Journal of Medical Internet Research (http://www.jmir.org), 08.11.2019.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in the Journal of Medical Internet Research, is properly cited. The complete bibliographic information, a link to the original publication on http://www.jmir.org/, as well as this copyright and license information must be included.

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Optics of the eye. A: With no refractive error, the image is focused properly on the retina, providing perfect uncorrected visual acuity. B and D: In hyperopia (far-sightedness; B) and myopia (nearsightedness; D) the image falls either behind or in front of the retina, respectively. C and E: Lenses can be used to re-focus the image on the retina, restoring visual acuity.