@article{ref1,
title="Trifocal lenses. A clinical study based upon 22,640 trifocal prescriptions",
journal="American journal of optometry and archives of American Academy of Optometry",
year="1951",
author="Bannon, R. E.",
volume="28",
number="5",
pages="254-274",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0002-9408",
doi="",
url="http://dx.doi.org/"
}