Trifocal and bifocal sunglasses are both kinds of multi-focal sunglasses, which is a combination of both sunglasses and multi-focal eyeglasses. However, trifocal sunglasses are an extension of bifocal ones, since bifocal sunglasses have two focus points while trifocals have three, which are the three regions for far, intermediate and near vision, respectively. The region in the bottom of the lens is basically for the near vision like reading, and the region in the top is usually for the far vision like scenery viewing. The added part in the middle is for the vision in the middle like computer watching, usually arm’s length.
Bifocal sunglasses make a great contribution to the old people for enabling them to have a clear vision of the nature in the sunshine both far and near. The problem is as they grow even older they are unable to see the intermediate objects clearly, either. So comes to the invention of trifocal sunglasses, which are more suitable for those people with advanced presbyopia problems. The additional segment for the intermediate vision is usually located above the reading zone, providing a gentle transition of vision change.
Trifocal sunglasses are available with a variety of types according to the different shapes and widths of the reading segment and intermediate segment. The most commonly type is the flat top 7×28 bifocals, also known as the D-segment. This type is 28 millimeters width in the reading segment and 7 millimeters high in the intermediate segment. Also, you can get the flat top 8×35 bifocals and executive trifocals, which both have relatively larger areas of the reading and intermediate parts, and they are quite useful for those people who sit in front of the computer for a long time. If you are not sure which kind of trifocal sunglasses you should wear, you can go to your doctor for a professional advice.
The common point between the bifocal and trifocal sunglasses is that they both have distinct division line among different zones, so the transition of vision areas will always cause some headaches or eye discomforts. Though the trifocal sunglasses are much better than the bifocal ones due to the intermediate segment, the phenomenon is unavoidable. Some wearers cannot endure the quick radical vision change at the beginning, so they are more likely to choose to wear the progressive sunglasses because the vision change is a gradual process in that kind of lenses and it is much easier for people to accommodate in the beginning. Therefore, trifocal sunglasses are becoming rarer as a result of the better effect of the progressive sunglasses, but it does not mean the trifocal sunglasses are not welcome at all. In fact, it has its own advantage and is popular with some kind of people.
Finally, as to the price of the trifocal sunglasses, they are a little more expensive than bifocal sunglasses, but cheaper than progressive sunglasses. You can choose either of them depending on your demands. After wearing them for a few days, I am sure you will find them worth the price and you can enjoy the clear vision of nature again.
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