Trifocals are reading glasses which have three divisions of correction on the lenses for clear vision, unlike the two corrections of bifocal lenses. Although the thought of looking through lenses having three lines etched on them might sound discomforting, it is actually easier to get used to than trying a bifocal lens. The logic is simple. While climbing stairs, instead of going from step 1 to step 3, it is easier to use step 2 as an intermediary to get to step 3 from step 1.
Trifocals are prescribed to those individuals who have acute conditions of presbyopia. These people need correction at near vision, intermediate length and at a distance. The intermediate correction is usually half of the reading addition. This means that a presbyopic patient diagnosed with -4 diopters provided with +3 reading addition has a net power of -1. Therefore, his or her intermediate correction is -2.5 diopters.
Trifocals are different from bifocals in the fact that the latter has only two regions of differentiation (near vision and distance vision) and the former has three distinct corrective regions. Hence trifocals provide the maximum clarity to the vision.
The near vision correction together with the intermediate is placed in a half circular space at the bottom of each lens. There is a thin line of demarcation between these two as well within the half circle.
The lowest segment of the half circle is for near vision. When the reader has to focus on objects closest to his or her eyes, he or she will have to look through this section of the lens.
Above it ,lies the intermediate zone. This part of the glasses is used to look through when objects are placed at an arm's distance. Although the intermediate range is the shortest, it can be adjusted to be made larger if needed by the user.
The top section of the lens is used to see anything beyond an arm's length. This section can be customized to suit other deficiencies in the patient's vision such as myopia or hyperopia.
Most individuals who have reached the age of forty and above will suffer from presbyopia sooner or later. Therefore, reading glasses are a must for patients. Presbyopia is a condition that occurs due to aging eyes. It is different from hyperopia, or farsightedness. Although the former cannot be prevented, it can be treated through laser surgery like Lasik surgery, or by wearing reading glasses or contact lenses.
Trifocals help the individual to look at all ranges of distance by using one pair of glasses. Therefore, there is no need to carry three glasses to use for different distances of vision. However, many people do not appreciate the lines present across the lenses of such reading glasses. For such individuals there is the option of progressive lenses. Also known as progressive add(ition) lenses (PALs), progressive power lenses, varifocal or graduated lenses, these lenses are free of any line or demarcation. Therefore, these types of glasses offer maximum comfort along with perfect clarity of vision for the wearer.
