Fish and insects guide design for future contact lenses
March 15, 2016 - 12:25 PM
Making the most of the low light in the muddy rivers where it swims,
the elephant nose fish survives by being able to spot predators amongst
the muck with a uniquely shaped retina, the part of the eye that
captures light. In a new study, researchers looked to the fish’s retinal
structure to inform the design of a contact lens that can adjust its
Imagine a contact lens that autofocuses within milliseconds. That
could be life-changing for people with presbyopia, a stiffening of the
eye’s lens that makes it difficult to focus on close objects. Presbyopia
affects more than 1 billion people worldwide, half of whom do not have
adequate correction, said the project’s leader, Hongrui Jiang, Ph.D., of
the University of Wisconsin, Madison. And while glasses, conventional
contact lenses and surgery provide some improvement, these options all
involve the loss of contrast and sensitivity, as well as difficulty with
night vision. Jiang’s idea is to design contacts that continuously
adjust in concert with one’s own cornea and lens to recapture a person’s
The project, for which Jiang received a 2011 NIH Director’s New Innovator Award
(an initiative of the NIH Common Fund) funded by the National Eye
Institute, requires overcoming several engineering challenges. They
include designing the lens, algorithm-driven sensors, and miniature
electronic circuits that adjust the shape of the lens, plus creating a
power source – all embedded within a soft, flexible material that fits
over the eye.
In their latest study, published in Proceedings of the National
Academy of Sciences, Jiang and his team focused on a design for the
image sensors. “The sensors must be extremely small and capable of
acquiring images under low-light conditions, so they need to be
exquisitely sensitive to light,” Jiang said.
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. Borrowing from nature, the
researchers created a device that contains thousands of very small light
collectors. These 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 have 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 micrometers, roughly the
width of the thinnest human hair.
They developed another type of 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. “Each microlense is made out
of a forest of silicon nanowires,” Jiang explained. 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. Wrap it around a laparoscopic surgical scope
and you’ve got a high-resolution, 360-degree view inside a patient’s
body. Mount it on a lamppost and you can see the surrounding
intersection from all sides.
In order to change focus, the contact lens will also need to be equipped with an extremely small, thin power source.
Jiang’s working solution: a solar cell that simultaneously harvests
electrons from sunlight, converting them into electricity, and that also
stores energy within a network of nanostructures. It works much the way
a conventional solar panel does, but the addition of storage capability
within a single device is novel, Jiang said. The device still needs
tweaking, but the team is optimistic that it will be powerful enough to
drive the lens yet small enough to fit the space available.
A prototype for clinical testing may still be five to 10 years off,
Jiang said. Once it’s available, however, it may not cost much more than
conventional contact lenses. “There’s a huge market for this and with
mass production, the cost is not likely to be a barrier,” he said.
The research was supported in part by NIH grant DP2OD008678 to Jiang’s lab.