Just as eyewear fashions have changed a lot recently, lenses have also improved. As technology has advanced, more options have become available to multifocal wearers.
Not so long ago, anyone who needed a correction to see close up had to wear the Franklin or Executive bifocal, with the line that goes all the way across the entire width of the lens. Then came the smaller, half-moon bifocal segment. And those who needed a correction in the intermediate zone (about arm's length away), had very few choices.
Nowadays, multifocal wearers have lots of options. They include special glasses for computers and other tasks that take place at the intermediate range, as well as lenses for reading distance and special combinations for unique work situations.
One Lens, Many Functions
Multifocals let you focus through different prescriptions at different distances through the same lens - hence the name. Bifocals (meaning a lens with two points of focus - usually one for distance and one for near) are the most commonly prescribed multifocal lenses.
Many people need some visual correction in order to read or see things close up. Often, bifocals are necessary because people's arms "become shorter" (actually a condition called "presbyopia") as they enter middle age and things closer to them become more difficult to see. But other conditions can cause people of any age to need more help seeing properly in the near range. Overconvergence, when the eyes work too hard to see close up, is one.
Regardless of the reason you need a prescription for near-vision correction, bifocals all work in the same way. A small portion of the eyeglass lens is reserved for the near-vision correction. The rest of the lens is usually a distance correction, but sometimes has no correction at all in it.
The segment that is devoted to near-vision correction can be in one of several shapes:
- A half-moon, also called a flat-top, straight-top or D segment;
- A round segment;
- A narrow rectangular area, known as a ribbon segment;
- Or a full bottom half of a lens, called the Franklin, Executive or E style.
Similar to bifocals are trifocals, or lenses with three points of focus - usually for distance, intermediate and near. Trifocals have an added segment above the bifocal for viewing things in the intermediate zone, which is farther than the near zone - about arm's length away. Computers are an excellent example of something that is in a person's intermediate zone. Motorists who need to see in the distance to drive, to see the gauges on the dashboard, and to read a map also would benefit from a trifocal. Flat-top and Executive lens styles are the most common trifocals.
How Multifocals Are Fitted
Bifocals are typically placed so the line rests at the same height as the wearer's lower eyelid. As a bifocal wearer drops his eyes downward to read, the eyes naturally seek out the near-vision portion of the lens.
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.
Most bifocals and trifocals have lines, but there is a round bifocal segment called the E-Z-2-Vue, which is less obtrusive. It is blended into the distance portion of the lens so that it is not readily visible to the casual viewer.
A progressive lens is a special kind of no-line multifocal that incorporates all corrections, from distance to close up, into one lens without any separation of the various visual zones by line.
Specialty multifocal lenses are designed to solve particular vision problems. If you have a special need because of your work, hobby, or favorite pastime, tell your eye care practitioner.
Multifocal Occupational Lenses
Other multifocals are suited for performing a particular job or hobby and are not meant for everyday wear:
One occupational bifocal is a Double-D, which has a half-moon-shaped flat-top bifocal at the bottom of the lens and an upside-down flat-top at the top of the lens. The rest of the lens area is for distance correction. Car mechanics, who need to see well at the near point both looking down to read as well as looking up above their head to work on the undercarriage of a car on a lift, would benefit from a Double-D. Double-round segs are also occupational lenses that can be used for the same purposes as the Double-D.
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 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.
Sometimes a common multifocal can become an occupational lens by changing the way it is placed in the eyeglass frame. For example, instead of placing a long, narrow rectangular ribbon seg just at the bottom eyelid, where bifocals are normally situated, the ribbon seg can be moved to reside at your eye level. You would then look through the near vision correction rather than through the distance correction when standing or sitting in a normal position. While this wouldn't be ideal for everyday tasks such as driving, it would work for a pharmacist who must read the small print on labels right in front of her all day long.
For golf players, flat-top bifocals are often placed extremely low and in the inside corner of one lens of a pair of "golf glasses." Just enough near vision correction is placed in the eyeglasses to allow the golfer to read and write on the scorecard without compromising the vision necessary to hit the sweet spot on the ball.
