Fish Retinas Inspire Adjustable Contact Lens Design

The elephant nose fish’s uniquely shaped retina has inspired the experimental design for a contact lens that can adjust its focus, a development that could enable autofocus lenses for people with presbyopia, the stiffening of the eye's lens that makes it difficult to focus on close objects.

Glasses, conventional contact lenses and surgery provide some improvement for presbyopia patients, but these options all involve the loss of contrast and sensitivity, as well as difficulty with night vision.

Many of the components for the contact lens — the sensors, electronics, solar cells — will be embedded along the edge of a flexible material. Courtesy of Hongrui Jiang.

The adjustable lens, conceived by Hongrui Jiang of the University of Wisconsin, Madison, would require a new design, algorithm-driven sensors and miniature electronic circuits that adjust the shape of the lens, plus a power source — all of which must be embedded within a soft, flexible material that fits over the eye.

Jiang and his team’s most recent work, published in Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1517953113), has focused on the design for the requisite image sensors, which must be extremely small and sensitive, capable of acquiring images under low-light conditions.

The team took their inspiration from the elephant nose fish's retina, which has a series of deep cup-like structures with reflective sidewalls. That design helps gather light and intensify the particular wavelengths needed for the fish to see, and the researchers created a device that contains thousands of very small light collectors.

The light collectors are finger-like glass protrusions, the inside of which are deep cups coated with reflective aluminum. The incoming light hits the fingers and then is focused by the reflective sidewalls. Jiang and his team tested this device's ability to enhance images captured by a mechanical eye model designed in a lab.

In separate studies, the researchers designed and tested a couple of different approaches for the contact lens material. For one approach, they formed a liquid lens from a droplet of silicone oil and water, which won't mix. The droplet sits in a chamber atop a flexible platform, while a pair of electrodes produces an electric field that modifies the surface tension of each liquid differently, resulting in forces that squeeze the droplet into different focal lengths. The lens is able to focus on objects as small as 20 μm.

The team also developed a lens inspired by the compound eyes of insects and other arthropods. Insect eyes comprise thousands of individual microlenses that each point in different directions to capture a specific part of a scene. Jiang and his colleagues developed a flexible array of artificial microlenses, with each lens made out of a “forest” of silicon nanowires.

Together, the microlenses provide even greater resolution than the liquid lens. The array's flexibility makes it suitable not only for contact lenses, but for other potential uses. The researchers suggest it could be wrapped around a laparoscopic surgical scope to achieve a high-resolution, 360° view inside a patient's body. The flexible array could also be mounted on a lamppost to view the surrounding intersection from all sides.