| 摘要 |
An improved single lens comprising: a continuous change in lens curvature going downwards; a front and a back surfaces; an upper part which front and back surfaces are top zones of front and back surfaces, covering at least the half of respectively front and back surfaces, and where the two top zones are aligned to each other such that the effective power of the upper part of the lens is constant; a lower part used for viewing near objects which front and back surfaces are lower zones of front and back surfaces, the front and back lower zones comprising each a surface zone where top to bottom increasing curvature of each surface zone is provided and where the two front and back lower zones are aligned to each other such that the maximum difference of the effective power of the lower part of the lens and the effective power of the upper part of the lens is comprised between 0 and 0.5 Diopter.
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