Tri-Focal Lenses: Flat-top 28mm
Trifocals come in a variety of designs. Flat top trifocals are the most widely used form. The added segment provides clear vision at arm's length distance, the area that is usually blurred for bifocal wearers. Trifocals are available in all lens materials.
Trifocal lenses are similar to bifocals, except that the two focal areas are separated by a third middle area with intermediate focus correction, used for intermediate vision, e.g. computer distance. This lens type has two segment lines, dividing the three different correcting segments.
Trifocals are fitted a bit higher, with the top line of the intermediate area placed even with the pupil. A trifocal wearer focuses through the intermediate prescription area of the lens when looking at something between 18 and 24 inches away. The eyes gravitate straight ahead, or up and over the multifocal segments, when gazing at something in the distance.
An E-D trifocal has a distance correction along the top half of the lens, separated from the intermediate correction in the bottom half by a line that goes all the way across the width of the lens in the Executive bifocal style, and a D half-moon segment containing the near correction that resides within the lower half of the lens. The E-D trifocal is for someone who must see at the intermediate distance in a wide field of vision and who also must see clearly both close-up and in the distance. A television production person, for example, who must keep an eye on several TV monitors spread out in front and to the sides while being able to read notes from a clipboard and recognize someone across the room, is a good candidate for this lens.
Example of Trifocal Lenses:
“Height x Width”
7x28 -- 7mm x 28mm
7x35 --7mm x 35mm
8x28 -- 8mm x 28mm
8x35 -- 8mm x 35mm
9x35 -- 9mm x 35mm (discontinued size)
10x28 -- 10mm x 28mm (discontinued size)
10x35 -- 10mm x 35mm (discontinued size)
DD FT 28 -- Double D Flat Top 28mm
DD FT 35 -- Double D Flat Top 35mm
Executive -- Executive Trifocals