Around the time you turn forty, along with the “over the hill” novelty gifts, you may start to notice signs of presbyopia. This is an age-related condition that makes you feel as though no distance is great enough to allow you to read comfortably. If you are already wearing glasses, you are probably looking at some sort of multifocal lens to make up the difference.
While progressive lenses are super popular, the benefits of traditional bifocals and trifocals cannot be ignored.
- There is a wider area on the lens for computer or reading
- With traditional bi- or trifocal lenses, there is more customization available for your needs
- You can have them designed specifically for computer work or other intermediate vision tasks
The functions of a lens
Multifocal lenses have two or more lens powers to offset presbyopia problems. Bifocal and trifocal have two and three, respectively. Progressives have an invisible change in the prescription from the top to the bottom of the lens. This requires the use of many lens powers in one lens.
In bifocal lenses, the bottom portion of the lens reduces how much effort it takes the eyes to focus. Multifocal lenses could also help children cope with myopia.
Regardless of your individual needs, bifocals work in the same way. A majority of the lens is dedicated to correct your distance vision, while a small part of the lower lens aides your near vision. All you have to do is look down when you are reading and up for the distance.
Trifocals focus on three things — distance, near vision, and intermediate. The intermediate section is above the near segment. It helps with things at arm’s length. A good example of this would be a computer.
How are they fitted?
For a pair of bifocal lenses, the line of the near segment is fitted to wear the lower eyelid and near segment line are parallel. Eyes will adjust to seek the near vision part of the lens instinctively.
Trifocals are fitted differently. The intermediate segment is even with the lower margin of the pupil. Again, instinctive muscle memory will cause the eyes to seek out the appropriate portion of the lens.
These are not intended for constant wearing. Instead, they are for hobbies or jobs that require them. A mechanic has different needs than a golfer, so their multifocal lenses are designed differently. This allows the wearer to have the field of vision requisite for their needs.
Anti-reflective and transition type multifocal lenses
Anti-reflective coatings make your eyes more comfortable by getting rid of distracting reflections. They also help when driving at night because more light is able to get into the eye. This coating actually makes the lines in bi- and trifocal lenses less noticeable. That makes sense because the light is not bouncing off of the junction lines.
Running back and forth between indoors and outdoors can be torture for those with light sensitivity. If you find that it bothers you, there are photochromic lenses (best known as transitions) that darken in sunlight. This also reduces glare! This technological advance can be used in a multifocal lens.
Dr. Joseph Cohen O.D.
Woodland Hills Optometrist
Get excellent service on a comprehensive eye care
19737 Ventura Blvd., Suite 201, Woodland Hills, CA 91364