Bifocals and trifocals allow people with limited vision to see objects at varying distances, but only by refocusing on the object from a different vantage. A scientist named Zeev Zalevsky responded to this problem by developing a lens that allows the user to focus on any distance out from 33 centimeters:
It involves engraving the surface of a standard lens with a grid of 25 near-circular structures each 2 millimeters across and containing two concentric rings. The engraved rings are just a few hundred micrometers wide and a micrometer deep. “The exact number and size of the sets will change from one lens to another,” depending on its size and shape, says Zalevsky.
The rings shift the phase of the light waves passing through the lens, leading to patterns of both constructive and destructive interference. Using a computer model to calculate how changes in the diameter and position of the rings alter the pattern, Zalevsky came up with a design that creates a channel of constructive interference perpendicular to the lens through each of the 25 structures. Within these channels, light from both near and distant objects is in perfect focus.
“It results in an axial channel of focused light, not a single focal spot,” Zalevsky says. “If the retina is positioned anywhere along this channel, it will always see objects in focus.”
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