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Occupational Bifocals and Trifocals: The Mid-Life Onset of Thickening Lenses
What are occupational bifocals and trifocals? An occupational lens is a special form of vision correction for the unique demands of a profession or hobby. Bifocal and trifocal lenses correct presbyopia, the mid-life onset of thickening of the lens that makes focusing on near objects difficult. Occupational bifocals and trifocals are special-purpose eyewear, not designed for everyday use, but nearly anyone over the age of 40 who needs bifocal or multifocal lenses can benefit from having a second pair in an occupational design. The Double-D bifocal is an occupation lens designed for professions that require a combination of reading and overhead near work. It has a D-shaped flat-top segment at the bottom of the lens and an upside-down D-shaped flat-top segment at the top of the lens. The middle of the lens provides distance correction. Who benefits from Double-D bifocal lenses? They are especially useful in auto maintenance and repair. The Double-D design allows mechanics to see clearly up close, whether they are looking down to read print or a number or they are looking up to work on a car on a lift. Mail clerks and hotel front desk clerks who need read documents and file them overhead also benefit from this design. The E-D trifocal design is for people who need clear vision everywhere, but especially when they are looking at objects at arm's length. This trifocal has distance correction in the top half of the lens. There is vision correction for intermediate distances, for objects about 18 in (45 cm) in front of the body, in the bottom half of the lens. Like the executive bifocal, there is a line across the lens separating the top and bottom halves of the lens. In the E-D trifocal, however, there is also a D-shaped segment at the bottom of the lens for clear vision of objects closer than 18 in from the eyes. Who benefits from E-D trifocal lenses? They are a good choice for anyone who needs corrected peripheral vision at arm's length, but who also needs to see at a distance and up close. Anyone who has to keep up with several TV monitors while being able to read notes from a clipboard and see action across the studio or room may benefit from this lens. The most common sports lenses are made for golfers. If you play golf and you wear multifocal lenses, you know they can be a problem. The close vision segments of bifocal, trifocal, and even progressive lenses distort your view of the ball. This can require you to tilt your head down into an uncomfortable position. Bifocals, in particular, make it difficult to line up a putt. The solution is a multifocal lens often called a" golfer's bifocal." A small, round segment is put very low in the corner of just one lens in a pair of bifocals. This way it is completely out of the way when you need to see the ball, but you still have vision to read your scorecard. Not all occupational lenses require special grinding. Sometimes a bifocal or trifocal lens can become an occupation lens simply by changing the way it is set into the frames. For example, bifocals usually place the near vision correction part of the lens at the level of the lower eyelid. Changing the way the lens sits in the frame, however, you can move this segment to eye level. The wearer then sees near vision correction rather than distance vision correction when looking straight ahead. This is not a good configuration of the lens for driving, but it may work very well for pharmacists and others who have to read small print on labels directly in front of the eyes all day long.
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