How Bifocal Contacts Work

Basics

People who need bifocals no longer have to wear little half-glasses in addition to their contacts. According to the Contact Lens Manufacturers Association, multifocal contact lenses are available in bifocal, trifocal and progressive levels. Bifocal contact lenses are designed to serve those with presbyopia, a condition common to people over 40 that causes the eyes to lose the ability to focus on near objects. Although they may seem odd at first, and cause double vision in bright lights and at night, the eyes eventually adjust naturally to bifocal contacts. Bifocal lenses are available as soft disposable contacts, soft gas-permeable lenses or as rigid permeable lenses, providing options for every contact wearer's preference.

Alternative Lenses

Alternative bifocal lenses are made with two prescriptions in each lens. They allow the eyes to shift between near and far objects as needed. Alternative bifocal lenses are slightly smaller then the average lens and rest in the center of the cornea, slightly above the lower eyelid. The eyes will turn downward and inward slightly to view objects that are nearby and up and outward to view objects at a distance. The bifocal portion of the lens in the lower half of the eye provides automatic sharper vision.

Simultaneous Lenses

Simultaneous vision bifocal lenses are made of concentric rings of varying prescription levels on each lens. The lenses allow the user to view near and distant objects at the same time with little or no transition. Light from near and far objects is being transmitted through both lenses at the same time however, so the brain receives both in-focus and out-of-focus objects simultaneously, requiring the brain to separate the sights. With a little time, averaging about two weeks, this function becomes automatic, though some people cannot make the adjustment.

Monovision

The least expensive and easiest to transition to are monovision bifocal contact lenses. Monovision lenses are available in common spherical shapes, making them easier to fit. Each eye contains a different prescription with monovision contacts. One lens corrects distance vision and the other lens is suited to correcting near vision. The eyes automatically adjust as needed and most contact wearers are not even aware of which eye is being used to compensate for the correction, report consultants at Presbyopia Contacts. Middle, 3-D vision is not corrected with monovision lenses and can be difficult for some people to adapt to.