Buying Glasses Help - Bifocal Lens Options

D25mm Segment
A standard bifocal lens with a flat-topped reading area set into the lens, in the form of a 'D' shape on it's side. This is an ideal type of bifocal for general use. It is one of the most popular types of bifocal, providing good clear distance and a moderately wide reading area.  For those requiring a very wide reading area, such as accountants and desk workers, there are the D28mm bifocal lenses.

R25mm Segment
This is one of the older types of bifocal lens, having a curved, 25mm diameter reading segment positioned at the bottom of the lens. One advantage it has over the newer 'D' segment bifocals, is that the bifocal segment is barely visible, providing a good cosmetic appearance. However, the overall performance of the lens is not as good as the 'D' Segment types. Special bifocals such as the photochromic (e.g. transitions) bifocals are only manufactured in the more modern 'D' type of lens.

D28mm Segment  
A bifocal lens with a larger 28mm D-shaped reading segment. Please see D25 Segment above, for fuller description.

D28mm Segment + Thinner Lens
A special, thinner version of our standard D28 bifocal lens. The material used in the lens manufacture is denser than standard, allowing flatter curvature to be employed to provide the same relative power. Furthermore, the lens can be made in aspheric format, a process which further 'thins' the lens, providing the best cosmetic appearance and freedom from unwanted distortions towards the edge of the lens. This makes for a very comfortable lens for prolonged use.

D28mm Segment Photochromic (grey) 
A special D28 bifocal lens which develops a grey tint in sunlight. The lens returns to its normal clear state when indoors. The process is not instant, as a lot of the advertising material would suggest, but depends on the level of UV light, and the ambient temperature. These lenses usually have some slight residual tint, even in the 'clear' state. It is, however, an excellent material for eye protection in the sunlight.

D28mm Segment Photochromic (brown)
A special D28 bifocal lens which develops a brown tint in sunlight. The lens returns to its normal clear state when indoors. The process is not instant, as a lot of the advertising material would suggest, but depends on the level of UV light, and the ambient temperature. These lenses usually have some slight residual tint, even in the 'clear' state. It is, however, an excellent material for eye protection in the sunlight.