The introduction of the first bifocal lenses by ZEISS as long ago as 1952 represented a real revolution at the time. In the recent years, however, the popularity of bifocals has considerably decreased due to the constant improvement in the quality of progressive lenses.
While a large number of segment shapes existed in the past, the type with a curved top is now the most common in most countries and is indicated in the product name by a "C" (curved). Fewer reflections result on the curved surface than on the straight edge of an S segment (S = straight). Today’s bifocal lenses from ZEISS therefore provide wearers with improved cosmetic benefits and enhanced functionality.
Bifocal lenses are available with two different segment widths: 25 mm and 28 mm. The number after the "CT" in the product name indicates the segment width in millimetres. The segment width of 25 mm is adapted to standard conditions of use, providing a sufficiently large visual field for reading purposes. The diameter 28 mm provides correspondingly wider fields of view.
For the segments of glass bifocals from ZEISS, materials with different refractive indices are selected deoending on the addition in order to ensure that, even with higher additions, all bifocal lenses are as thin and flat as possible.
The bifocal lenses ZEISS Bifocal Classic CT25 and ZEISS Bifocal Classic CT28 are available in various materials: in the form of medium index glass, as photochromic and plastic lenses.