People over 40 mostly find their eyes lose their capacity to adjust and focus on different things. This is a common biological change. As body ages, our eyes age as well, resulting in presbyopia, a term derived from Latin with the meaning of ‘ageing eyes’. This is different from myopia and hyperopia which are caused by deficiency of eyes and can not be cured by corrective glasses, refractive surgery or contact lenses. People with presbyopia usually use trifocals.
Trifocals are glasses where the lenses have 3 regions to correct for distance, intermediate (arm’s length), and near vision. They most used by people with advanced presbyopia who have been prescribed 2 diopters or more of reading addition. Compared with bifocals, trifocals provide more clear vision to the wearer although, in some degree, they sound to be tougher to see through.
Those who have ever worn bifocal glasses may know that at the very first time when they wear them, they often feel hard to get used to bifocals. They frequently feel dizzy. The insertion of the intermediate addition of trifocals which steps between the distant and reading distance make things easier for a person to progress one step to another. The intermediate addition is normally half of the reading addition and half of the long addition. So for someone with a distance prescription of -4 diopters and a reading addition of +3 diopters, the reading portion of their trifocals would have a net power of -1, and the intermediate segment would be -2.5 diopters. Thus, those wearing trifocals obtain clearer vision and experience less strain on the eye than those wearing bifocals.
Therefore, we can see, based on the same principle, trifocals, only differing from bifocals in vision of divisions, are equipped with three additions rather than two. Trifocal is a type of glasses belong to multifocal glasses.
Just like bifocals, trifocals are also equipped with the semi-circular area with each the reading addition and distance addition. Meanwhile the mid-range of trifocals are equipped with a narrow band, for people seeing things that are not very far but further than the reading distance. If you frequently spend your time before a computer, trifocals will provide you with great comfort.
Trifocals offer the wearer the benefits of three corrective prescriptions without the need for three separate pairs of glasses. For those who want the benefit of trifocals without telltale lines, there are progressive lenses, which may also be called progressive addition lenses or PALs, progressive power lenses, graduated lenses and varifocal lenses. These terms may be used to describe ‘no-line’ bifocals as well.