| 摘要 |
The lens has an aspherical surface having a zone for far vision, a zone for near vision, and between these two zones, a zone for intermediate vision, with a meridian curve along which the curvature of the surface varies progressively and which is inclined from top to bottom towards the nose side of the lens, at least in the intermediate zone. A portion of the meridian curve situated in the intermediate and near zones is divided into a first segment at an angle alpha to the vertical where the value of alpha is an increasing function of the power addition A of the lens, and a second segment at an angle omega to the vertical where omega is smaller than alpha . At the point where the two segments meet, the mean sphere value of the surface corresponds to a power addition lying in the range 0.8 to 0.92 times the nominal power addition of the lens.
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