In the journals: Studies find ways to reduce falls in older multifocal lens wearers
Poor vision increases the risk of falling, and wearing glasses helps reduce that risk — usually, but not always. If you wear multifocal lenses — that is, bifocals, trifocals, or progressive lenses — you've probably had occasional trouble negotiating steps, curbs, or uneven ground. Scientists investigating this problem think they know why: when we walk, we normally see the ground from a distance of five to six feet, but the focal length of the lower segment of multifocal lenses is only slightly more than one foot. Consequently, our view of the ground is blurry. Depth perception as well as contrast sensitivity (the ability to distinguish objects from their background) is impaired at precisely the distance you need to detect and avoid ground-level obstacles. Also, progressive lenses can produce visual distortions at their periphery, and bifocals can cause a jump in image at the divide between the close-up and distance segments of the lenses. Several studies have shown that wearing multifocals increases the risk of trips and falls in older people.
But for many people, wearing single-focus lenses all the time just isn't an option. Presbyopia, the most common form of visual impairment in older adults, reduces close-up vision and may create a need for corrective lenses for both near and far vision. That means either separate pairs of glasses for close-up and distance vision or multifocals, which allow you to focus at two or more distances through the same lenses.