posted from: http://www.paceyemd.com/blog/when-should-you-get-a-multi-focal-lens/

For most of us, the decision to get a multi-focal lens is more of a “when” rather than an “if” scenario. While nearsightedness and farsightedness typically develop in youth, the need for a multi-focal lens is brought on by the natural aging process and affects nearly all of us at some point in our lives.
Presbyopia
An eye condition called presbyopia is what creates the need for a multi-focal correction. Much like myopia (nearsightedness) and hyperopia (farsightedness), presbyopia involves the inability of the eye’s lens to focus correctly. This condition is uncommon in younger individuals but ends up affecting most of us around age 40 to 45. When presbyopia occurs, the eye has trouble focusing on up-close objects, creating a need for vision correction at reading distance.
Bifocals, Trifocals & Progressives
Some people are fortunate enough to have good eyesight without correction—when presbyopia occurs, they can often get by with over-the-counter “readers” that provide up-close correction. Those who need correction for other eye conditions in addition to presbyopia usually need a prescription for bifocals, trifocals or progressive lenses:

Bifocal: Provides two areas of correction, for near and distance.
Trifocal: Three areas of correction—near, distance and an intermediate middle zone for specific activities.
Progressive: A gradual progression lens that offers the widest range of correction. This lens is shaped to allow correction at nearly any distance, based on which part of the lens is looked through.

So which option is best? As with any prescription, it depends on your personal needs. Those who require correction at the intermediate distance (the distance we typically sit from our computer screens) may benefit from the increased vision flexibility of trifocal and progressive lenses. Speak with your optometrist or ophthalmologist to see  which vision correction option will be best suited to your lifestyle.