Trifocal glasses are available in several options. Here in this article you will learn about the differences between them and who should buy this special lenses.
Trifocal glasses only come into consideration when normal bifocal lenses limit the the intermediate distance too much. In some cases when the support of the reading power gets higher the wearer of the bifocals has to increase the distance looking through the upper portion of tthe lens or decrease the distance looking att the lower part of the lens in order to see it clear.
This is the main reason for trifocal lenses. It gives the wearer with a high reading power the ability to see clearly in a intermediate distance which the wearer could not do with bifocals. Compared to progressive lenses the area for the intermediate distance is a lot bigger with trifocal glasses. But these days you seldom see people with trifolcas due to the two visible lines in frontt of the eyes of the wearer.
Here in the picture below you can see how the different zones of trifocal glasses are positioned in frontt of an eye. Usually the upper visible line is placed directly in front the lower end of the pupil.
Advantages of Trifocal Glasses
- Excellent visual acuity in the distance and near and in an intermediate distance of approx. 45 cm to 80 cm for people with a high addition value (more than 2.25D)
- Large field of view in the reading distance
- No blurred areas in the periphery
- Constant size of the near fields at higher reading power
- different prescriptions for prisms and astigmatism in distance and near areas are possible
Disadvantages of Bifocal Glasses
- Visible lines
- Image jumps
From a technical point of view people sometimes have trouble acoomodating to the image jumps. This means the perceived image moves hops a little when the wearer switches from distance vision to one of the reading areas. This has something to do with the position of the optical center in the near segment. Depending on shape of the segment the mentioned image jump can be reduced.
From the cosmetic point of view, trifocals are much more conspicuous than bifocals or varifocals because of the visible demarcations. Although the clear demarcations act as an orientation, they can also be perceived as disturbing visual edges.
What Types of Trifocal Are Available?
The selection of trifocal lenses is very large. Often the optician only needs to know the right manufacturer and the customer gets the desired lens design. For example, the wearer of the trifocals may wish to maximize the intermediate distance area or the reading area. All of this is possible. Take a look at the diagram below.
Every manufacturer has their own options when it comes to trifocals. You can often choose between different sizes and designs but when it comes to other options like lens materials the options are a lot more limited compared to progressive or bifocal lenses. Here in the list below you can see some manufacturers in combination with their lensdesigns.
- ZEISS Trifocal Classic S728
- Shamir Trifocal 35 or 28
- Kaps Vision F7x32x24
Some of the trifocal lenses on the market have an edge on the surface of the lens while other lenses have a smooth surface. With glass trifocal lenses, you can choose both options. If you prefer plastic, you will find a ledge on the surface. Here below you can see the available differences in a list.
- Fused trifocal lenses made out of glass
- Solid trifocals made out of glass
- Plastic trifocal glasses
The big advantage of a lens without a ledge, is that the near part is less visible and also the lens is easier to clean.
Do Trifocal Lenses Have Lines?
Trifocal lenses have two visible lines in each lens. Each of the visible lines is centered below the pupil of the wearer. The smaller the lens segments are for the intermediate distance and reading the less perceivable the visible lines become.
Some of the trifocal lens designs do not only have visible lines but also a ledge right where the lens segments for the intermediate distance are placed.
How Do Trifocal Glasses Work?
Trifocal glasses work due to different radii found in the upper, middle and lower parts of the lens. Each lens segment thus receives the optimal lens prescription for seeing in the distance, the intermediate range or even for reading.
In practice, this works very easily for the wearer of the glasses. When you look forward, the glasses are adjusted so that you look through the distance part of the glasses. As soon as the gaze is lowered a little, the eyes look through the field for the intermediate distance. Here you can see sharply between one meter and 40cm.
If the gaze is tilted even more, you look through the area with the lens thickness for reading. Here you can only see sharply at a distance of about 40cm.
How Much Does Trifocal Glasses Cost?
Trifocal lenses are priced pretty quickly between $400-800 for both lenses. However, special customizations such as the special size or shape of a lens segment can increase the price to over $1000.
Can I Order Trifocal Glasses Online?
Trifocals can be ordered online. However, the offer and advice online is very limited compared to a local optician. There are no measurements performed online. However, the measurements are necessary to achieve an optimal result with your trifocals in the end.
It is better to simply visit your local optician. He or she can ask you the right questions and can give you a recommendation based on his or her experience with different trifocals.
Trifocal Lenses for Computer
Trifocals are not well suited for use on the computer. The reason for this is that when wearing trifocals in combination with a natural head and body posture, you look through the upper part of the lens when sitting in front of a desktop PC. But you would have to look through the middle part to see the screen sharply.
You could achieve this by tilting your head back. Then you can see through the lens at a lower point. But this unnatural neck position will quickly lead to tension and other problems in your neck and shoulders. Therefore, opticians do not recommend it. PC glasses work better here. You can get more information here.
However, if you want to use a laptop in combination with trifocals then this often works well. The reason is that when you use the laptop, you usually look down anyway and the screen is smaller. This means you can stay in your natural head and neck position and are not even particularly limited by the visual range of the trifocals.
Out of experience I can say trifocals are a great alternative to progressive lens if the wearer can handle the subtle lines in the trifocals. The width of the reading areas is a five to 10 times bigger compared to a progressive lens design. After the wearer got a little experience over one to two weeks they learn to love their trifocals and do not want to miss them anymore.