@article{ref1,
title="Effects of age on visibility",
journal="American journal of optometry and archives of American Academy of Optometry",
year="1957",
author="Guth, S. K.",
volume="34",
number="9",
pages="463-477",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0002-9408",
doi="",
url="http://dx.doi.org/"
}