Do you require bifocals? Some time after age 40, you will begin to see the symptoms of presbyopia, including that feeling that your arms “aren’t long enough” to hold a newspaper or magazine at a position where you can read it clearly.
If you already use prescription glasses, this typically implies you will need to start wearing multifocal lenses to continue to see plainly at all ranges.
While a lot of presbyopes nowadays pick line-free progressive lenses, traditional bifocals and trifocals have some benefits over progressives. In specific, bifocal and trifocal lenses normally offer wider lens areas for reading and computer work than progressive lenses.
Also, there are numerous special-purpose bifocal and trifocal lens designs offered, consisting of unique glasses for computers and for other jobs that require exceptional intermediate and near vision.
What Are the Functions of Multifocal Glasses?
Multifocal eyeglass lenses include two or more lens powers to help you see objects at all distances after you lose the capability to naturally alter the focus of your eyes due to age (presbyopia).
Bifocals consist of two lens powers; trifocals have three. Progressive multifocal lenses gradually alter in power from the top half of the lens to the bottom, and thus contain many lens powers.
Though multifocal lenses generally are recommended for adults over age 40 to make up for presbyopia, sometimes bifocals are prescribed for children and young people who have eye teaming or focusing issues that cause eye strain when reading.
In these cases, the bottom part of the bifocal lens minimizes the quantity of focusing effort required to see near items plainly.
Also, some research recommends using bifocals or other multifocal lenses may help manage myopia in some children by minimizing the focusing needs of reading and near work.
No matter the reason you need a prescription for near-vision correction, bifocals all operate in the exact same way. A small part in the lower part of the lens contains the power required to fix your near vision. The rest of the lens generally is for your distance vision.
The lens section (or “seg”) committed to near-vision correction can be among a number of shapes:
- A half-moon – also called a flat-top, straight-top or D segment
- A round sector
- A narrow rectangle-shaped area, called a ribbon sector
- The complete bottom half of a bifocal lens, called the Franklin, Executive or E style
Generally, you look up and through the distance part of the lens when concentrating on points farther away, and you look down and through the bifocal sector of the lens when focusing on reading material or objects within 18 inches of your eyes.
Trifocals have three points of focus – generally for distance, intermediate and near vision. The intermediate section in trifocal lenses is directly above the near seg and is used to see objects at arm’s length.
Computers are an outstanding example of something that is in a person’s intermediate zone. Motorists who have to see in the distance to drive, to see the assesses on the dashboard, and to read a map also would benefit from a trifocal.
The most popular trifocal designs are the flat-top and the Executive.
How Bifocal and Trifocal Lenses Are Fitted
Bifocals generally are placed so the line rests at the same height as the wearer’s lower eyelid.
As a bifocal user drops his eyes downward to read, the eyes naturally seek out the near-vision part of the lens.
Trifocal glasses are fitted a bit higher, with the top line of the intermediate seg placed even with the lower margin of the pupil.
A trifocal wearer checks out the intermediate zone when seeing something in between 18 and 24 inches away. The eyes gravitate straight ahead, or up and over the multifocal sectors, when gazing at something in the distance.
Bifocals and trifocals have noticeable lines, but the line in a round-seg bifocal tends to be less noticeable than the lines in flat-top and Executive designs.
There is something called an “invisible bifocal,” which basically is a round-seg bifocal with the noticeable line buffed out. This blending procedure, nevertheless, causes some optical distortions.
If you wish to use a multifocal lens without noticeable lines, progressive lenses generally are your best option.
Occupational Bifocals and Trifocals
Why do people need bifocals? “Occupational” multifocal lenses are designed for carrying out a specific job or hobby and are not meant for general-purpose wear.
One popular occupational multifocal lens is the “Double-D.” This lens has an upside-down flat-top sector for near or intermediate vision in the leading third of the lens and a 2nd flat-top segment for near vision in the bottom third.
The center of the Double-D multifocal lens is for distance vision. Depending upon the lens power in the top section, the Double-D can be thought about a trifocal or a bifocal lens.
The Double-D multifocal lens is excellent for car mechanics, who have to see their tools and other near objects, but also have to deal with cars on a lift above them.
The upper sector of the Double-D assists them see the undercarriage of the vehicle without needing to tilt their head far backwards, or wear their glasses upside-down, as they would need to do if they wore a conventional bifocal.
Another popular occupational multifocal lens is the E-D trifocal. This special-purpose trifocal lens has an Executive-style intermediate segment in the bottom half of the lens, and a smaller sized flat-top seg for near vision embedded within the intermediate seg.
The E-D trifocal is an excellent option for somebody who requires a very wide field of view for items at arm’s length and also should see plainly both close-up and in the distance. A television production individual, for example, who should watch on a number of TV screens spread out in front and to the sides while being able to read notes from a clipboard and acknowledge someone across the space, is a good candidate for this lens.
In some cases a typical multifocal lens can end up being an occupational lens by changing the method it is positioned in the spectacles frame.
For instance, golf enthusiasts over age 45 regularly grumble that the near portion of their multifocal lenses (including progressive lenses) gets in the way when they resolve their golf ball or try to line up a putt.
The solution? An occupational multifocal lens typically called a “golf player’s bifocal.”
In this lens, a little (generally round) near segment is placed in the lower outside corner of simply one lens. If you are right-handed, it’s put only in the right lens; if you are left-handed, it’s positioned in the left lens.
In this position, the near seg is entirely from your way when you’re on the course, but it still offers you enough near vision to read your scorecard or a menu for lunch in the clubhouse.
For more examples of occupational multifocal lenses for your specific requirements, seek advice from your eye care practitioner.