Human/insect lens adds depth to wide-angle views

A new lens that combines the focusing ability of the human eye with an insect’s wide-angle view could improve surgical imaging or help make a confocal microscope with no moving parts.

“Our eye can change focus. An insect eye is made of many small optical components that can’t change focus but give a wide view. We can combine the two,” said Dr. Yi Zhao, associate professor of biomedical engineering and ophthalmology at The Ohio State University. “What we get is a wide-angle lens with depth of field.”

Zhao’s prototype lens is made of a flexible transparent polymer filled with a gelatinous fluid similar to that inside the human eye. The lens is actually a composite of several separate dome-shaped fluid pockets, with small domes sitting atop one larger dome. Each dome is adjustable, so that as fluid is pumped into and out of the lens, different parts expand and contract, changing the direction and focus of the lens.

This shape-changing strategy is somewhat similar to the way muscles in the human eye change the shape of the lens tissue to achieve focus. It differs dramatically from the way typical cameras and microscopes focus, which is by moving separate glass lenses back and forth along the line of sight. The difference potentially could offer the same focusing capability as multiple moving lenses in a single stationary lens, which would make for smaller and lighter cameras and microscopes.

Dr. Yi Zhao of Ohio State University holds a prototype polymer lens (center) that combines features of both the human eye and the insect eye.

In particular, Zhao is interested in using the lens in confocal microscopes, which use a system of moving glass lenses and a laser to scan 3-D images of tiny objects.

“We believe that it is possible to make a confocal microscope with no moving parts,” he said.

Zhao and doctoral student Kang Wei demonstrated in tests that the lens could switch its focus among microscopic objects arranged at different distances. In one test, they printed the letters in O-H-I-O on top of tiny platforms of different heights and pointed the lens at them from above. The lens could focus on each letter in turn, while the other letters became more or less blurry, depending on how far away they were.

While the prototype worked well, its design wasn’t entirely practical, in that it required an external fluid reservoir, and the fluid had to be pumped in and out by hand. To make it more appropriate for use in electronics, the engineers created an otherwise identical shape-changing lens from an electrically active polymer, which expands and contracts based on electrical signals. That lens has undergone initial testing, and a paper on it has been submitted to an academic journal.

With further development, the technology could be useful in laparoscopes for medical testing and surgery.

A lens under development at Ohio State University combines features of the insect eye and the human eye to achieve wide-angle views with depth. Photos by Jo McCulty, courtesy of Ohio State University.

With laparoscopy, doctors insert tiny wide-angle cameras into the patient’s body to see as much tissue as they can without cutting the patient open. But such lenses don’t offer a sense of depth: They show all objects – both near and far – in focus at all times. This poses a problem for doctors; if they mistake a close object for a distant one, they could accidentally graze healthy tissue with the scope or surgical instruments.

“With our lens, doctors could get the wide-angle view they need and still be able to judge the distance between the lens and tissue. They could place instruments with more confidence and remove a tumor more easily, for example,” Zhao said.

The lens ultimately could find a home in smartphones. Because phone cameras don’t have moving parts, they use a fixed-focus lens, which eliminates depth. Phone cameras can’t truly zoom in on objects, either. They just crop an image and enlarge it, which greatly reduces quality. With a shape-changing lens, a phone potentially could take pictures with the same depth and zoom as a more expensive digital camera.

At 5 mm across, however, the lens is a little bigger than a typical smartphone lens, so Zhao and Wei plan to shrink the design.

The work was described in the Technical Digest of the 25th IEEE International Conference on Micro Electro Mechanical Systems. The university is seeking industry partners to license the technology.