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Don't throw away those bifocals just yet, but scientists have developed prototype spectacles that change prescriptions with the flick of a switch.
The new glasses could benefit people suffering from presbyopia, a condition in which faraway objects are in focus but those nearby appear blurry.
Presbyopia is a natural, age-associated progressive loss, and scientists estimate that about 90 percent of people over 45 suffer from it.
Many scientists believe presbyopia is caused by reduced elasticity of the eye's lens over time. Eventually the cornea—and other eye muscles that change lens shape to focus—can't overcome the lens' rigidity.
Doctors commonly prescribe bifocals, which have a small window on the bottom half to correct close-range vision. But bifocals can cause eye strain, a wearer has to constantly shift line of sight, and the field of vision is limited.