Trifocals are aimed at those people who have serious eye sight problem, especially presbyopia. These are recommended for serious sufferers of presbyopia. There is an intermediate correction that one has to get used before going on to using trifocal lenses. Most people suffering from presbyopia need correction of three things: near vision, intermediate length and distance correction. So, by correction one means that if a patient has -4 diopter, as the main problem and is given +3 reading addition, he ends up with having -1, as the power then intermediate rectification is of -2.5 diopters.