Tri-Focal Lenses: Flat-top 28mm
Trifocal lenses are designed to correct presbyopia. Trifocal lens has three optical zone with a sharp transition refractions. The optical zone for distance vision occupies a large portion of the lens and is located in its upper part, the zone for near vision at the bottom of the lens and is displaced to the nasal side, and the optical zone provides vision in the middle distance, is above the segment for near vision.
Trifocals lenses have three centers focusing - for remote distance, intermediate and near vision. The intermediate segment trifocal lens is just above the segment for near vision and is used to ensure that you might consider objects at arm's length.
Computer - an excellent example of an object located in the zone of intermediate vision. Motorists who at the same time you need to look at the road, the sensors on the dashboard and to read the map, also appreciate the advantages of trifocal lenses.
Trifocal lens set slightly above the top line of the intermediate segment.
The owner of trifocal lenses looks through the intermediate zone, considering that an approximately 18-24 inches. The look is directed forward or up and over the multifocal segment when you look at an object in the distance.