Ordinary and occupational multifocal lenses

Friday, November 13th, 2009 at 2:16 pm Post in Eyeglasses

Technological improvement of eyeglass lenses has brought much more options to customers. The period in which people with presbyopia were forced to wear the Franklin style bifocal lenses with visible lines across the lens has gone forever. Currently, new types of multifocal lenses are available, not to say various specialty eyeglasses such as computer glasses exclusively for intermediate vision.

Presbyopic people need visual correction to see close-up objects. Bifocal lenses are the most common type of multifocal lenses, which have more than one focal point for different vision. A bifocal lens has a bottom section for close vision and an upper section for distance vision. Nowadays, the bottom portion for close up vision can be various shapes: half-moon, round, narrow rectangular and full bottom half (the Franklin style). The wearer should look down and through the close segment of the lens to perform close work and look up and through the distance portion for far away vision. Trifocal lenses have three focal points, one of which for intermediate vision is a plus to bifocal lenses. Computer glasses are particularly for the wearer to see objects in the intermediate zone.

The fitting of bifocal lenses and trifocal lenses require some skills. The line of a bifocal lens should be placed at the same height as the wearer’s lower eyelid, and the top line of the intermediate area of a trifocal lens should be placed even with the pupil. These visible lines on multifocal lenses are useful in fitting, even though they affect the lens’ appearance.

Various multifocal occupational lenses are created to meet the needs for special jobs or hobbies. A Double-D bifocal lens has a half-moon-shaped flat-top bifocal at the bottom of the lens and an opposite one at the top of the lens. This type of occupational lenses benefits car mechanics.

An E-D trifocal lens has an upper half segment for distance vision. In the bottom half segment, there is a D half-moon section for near vision and the remaining part is for intermediate vision. A television production person is a good candidate for this lens type.

Special occupational multifocal lenses can be achieved simply by placing regular multifocal lenses in an unusual way. A pharmacist needs to read close-up labels all day long, which requires much time of close vision. In this case, ordinary bifocal lenses should be placed to reside at the eye level, so that the pharmacist can look through the near vision correction when standing or sitting in a normal position. For a golf player, flat-top bifocals should be placed particularly low to offer sufficient distance vision.