Trifocals are a special type of reading glasses. In these, you get three divisions on the lens for correction of vision, unlike bifocals, where you have just two such divisions. You might think that it will be difficult to read through a pair of glasses with three lines etched on it, but this is actually pretty easy to get used to. At any rate, you will find trifocals more convenient than bifocals once you have adjusted to them. Think about climbing. It's easier to reach step three via step two and not directly from step one. So with three marked vision zones, your eyes will have the time of their lives.

Doctors advise people with extreme presbyopia to use trifocals instead of bifocals. If you are one of them, you will need corrections for all ranges of vision, whether it is nearby, or intermediary, or a far off distance you are considering. There are complicated calculations to tell you what your net optical power is going to be. Optical power is measured in a special unit called diopter.

Bifocals can offer correction only at two ranges of distance, that is to say, near vision or distance vision. Trifocals will offer correction at all ranges of distance. As a result, you get the best and most clarified vision with trifocals.

Trifocals are not just for any person who has some problems with their sight. It is only for those who have a serious kind of presbyopia. With trifocal lenses, it is the intermediate distance correction that takes a little bit of getting used to. For instance, if you have a power of -4 diopters and a correction of 3 units, you end up with a power of -1. The intermediate correction for such a case will be-2.5.

o Even a lay person can understand why you get distinctly better vision with trifocals rather than bifocals. These give you three levels of correction while bifocals give you only two.

o Whatever modification is done to your lens is done to the lower section of the lens. The shape of the etched line will be that of a semi circular arc. The areas on the lens for near and intermediate vision are clearly demarcated by a thin line.

o The problem of short sightedness is dealt with by a special region near the bottom of the lens. So you don't need to fret about that.

o The part for intermediate rectification lies above the short sighted correction area. This won't cover a great range of distance, but will enable you to see clearly those things which are not near and not very far off either.

With a single pair of trifocals, you can tackle all problems related to presbyopia. You might encounter a problem with the lines of demarcation in these specs. If you are one of them, go for progressive lenses. They are as effectual as trifocals. In fact, they are more comfortable as the vision zones are not demarcated with a line. You get the best comfort and clarity of vision.