Contact lens
design for presbyopia
(March 14, 2016) 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 focus.
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 youthful vision.
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.