Language: Spanish
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Page: 179-186
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Arquivos Brasileiros de Oftalmologia
Vol 67 - N 3 - 2004

Progressive lenses X multifocal lenses: a study based on the analytic geometry of the cone
Araújo, Marília Cavalcante; Monte, Fernando Queiroz
PURPOSE: To understand, by means of illustrations and mathematical functions of the cone, the progressive lenses and to show that they are not multifocus lenses because in these the light refraction does not obey the laws of the Euclidian geometry. METHODS: A study was carried out on the analytic geometry of the cone, with a computer program called Auto-CAD 14 focusing on the geometric illustrations obtained with its section. RESULTS: Through the analysis of the obtained illustrations of the cone section we could observe that: the surfaces that compose the progressive lenses are made of ellipse, circle, parabola and hyperbola. Differently from literature, we found the ellipses with a larger diameter and the same direction followed by parabola and posterior hyperbola and not the other way. CONCLUSIONS: Unlike the multifocus lenses, the progressive lenses present prisms in the optical centers as a consequence of their structure. We analyzed their forms showing the theoretical limit of these evolutions.