ZEISS Single Vision Aphal 1.5 is a plastic, aspheric lenticular lens specially designed for high hyperopia and aphakia. With a refractive index of 1.501, ZEISS Single Vision Aphal is the optimum solution: it is light, has a high Abbe number, i. e. low dispersion, and provides excellent visual quality thanks to the asphere in its aperture.
Hyperopic patients requiring high plus powers are very demanding: they want lenses which are not only as light as possible in order to reduce the weight of their spectacles, but which also provide them with optimum visual quality. This means that the pronounced astigmatic error typical of high plus powers and which wearers find particularly irritating must be corrected to the greatest possible extent. High index plastic material would, of course, make it possible to produce thinner lenses, but increased dispersion would severely impair visual comfort.
The special benefit of ZEISS Single Vision Aphal 1.5 lenses is their aspheric front surface specially designed for high plus powers. It features a curved continuous transition zone between the aperture and the flattened margin (flattened margin asphere).
The aspheric surface design of the aperture provides the excellent visual quality also associated with the aspheric design of ZEISS single vision lenses.
The special aspheric design also makes the lens flatter. This reduces the "shape factor" or effective magnification of the lens, i. e. the wearer’s eyes look less magnified. Apart from its optical and cosmetic benefits, the asphere also results in a weight reduction compared to ZEISS Single Vision Sph 1.5 or glass lenses and hence also in enhanced wearing comfort. The thinner marginal zone allows standard frames to be glazed without difficulty.
In standard lenticular lenses, in both the plus and minus ranges, there is an abrupt transition between the aperture and the margin. This leads to a sudden change in the dioptric power at the optical dividing line, resulting in a ring-shaped gap in the visual field ("ring scotoma") which markedly impairs orientation.
The margin asphere in ZEISS Single Vision Aphal 1.5 lenses prevents ring scotoma, as the dioptric power changes continuously between the aperture and the edge of the lens. The wearer enjoys a full field of view and unimpaired orientation. The lenses have no ring scotoma. Although acuity is reduced in the peripheral zone of the lens due to the margin asphere, it is sufficient for peripheral vision.