Nanophotonics-based implant may enable at-home IOP monitoring

Take home:

A nanophotonics-based device implanted in the eye may one day enable patients with glaucoma to monitor their IOP from home.

By Vanessa Caceres; Reviewed by Hyuck Choo, PhD, and David Sretavan, MD, PhD

A sensor the size of four strands of hair may be used one day to monitor IOP in patients with glaucoma.

Three years ago, David Sretavan, MD, PhD, professor and vice chairman, Department of Ophthalmology and Physiology, University of California, San Francisco, heard about the possibility of making miniature nanophotonic sensors for IOP measurement from Hyuck Choo, PhD, now assistant professor of engineering, California Institute of Technology, Pasadena.

“I was interested in this because of the pressing clinical need in glaucoma for a much better IOP sensor,” Dr. Sretavan said.

Current IOP monitors could benefit from more accuracy, the researchers said.

“Right now, the devices are indirect and make assumptions about the thickness and curvature of the eye,” Dr. Choo said.

Additionally, IOP measurement usually takes place in the office only a few times a year.

Device details

The device co-developed by Dr. Sretavan, Jeong O. Lee, PhD, and Dr. Choo would be about 100 to 200 µm in diameter-just the size of a few strands of hair-and would interact with near-infrared light to obtain a measurement.

“You would point a handheld detector toward the eye for just a fraction of a second to get a reading,” Dr. Choo said.

The near-infrared light is not visible to the human eye, nor is it a laser, so Dr. Choo characterizes it as a nonintrusive, safe way of obtaining the IOP.

The sensor has a sealed cylindrical chamber and gold nanodot arrays on flexible membranes that form the top and bottom chamber surfaces, according to the researchers.

“When interrogated with light, the reflected signal from the device shows maximal reflectance dips at specific wavelengths and is the spectral signature of a unique gap size between nanodot arrays,” they said.

When IOP rises, the nanodot membranes deform, which would cause the gap between the arrays to decrease.

“This gap narrowing causes the reflectance spectrum to shift and is detected remotely via a spectrometer,” they added.

The sensor is called nanophotonics-based because photonics structures strongly enhance the opto-pneumatic signature in the reflected light, Dr. Choo said. It’s called nano because of its small size.

“This is much smaller than larger scale optics but equally effective,” he said.

There are other IOP sensors in development, but they are larger sized and require an antenna to be placed in the eye itself.

Right now, reading measurements from the device takes place via a tabletop-sized remote set up, but researchers eventually would like to change that to something that is handheld or that could even be embedded onto a television screen, computer screen, or a bathroom mirror. Eventually, users may be able to obtain readings from the device with their cell phones, Dr. Sretavan said.

One advantage of this device would be the ability to measure IOP on a more regular basis and at different times throughout the day since IOP often fluctuates, Dr. Sretavan said.

“Typically, glaucoma patients only get their eye pressure measured three or four times a year when they visit the doctor,” he said.

He contrasted this with patients who have high blood pressure and are able to check their blood pressure at home with easy-to-use devices, noting that this could lead to more optimal management of IOP tailored to the pressure profiles of individual patients.

What’s next for the device

Researchers are preparing to do preclinical studies and hope for results by the end of the year. They have implanted prototypes into rabbit eyes.

One area they will examine in the preclinical work is biocompatibility. However, the material used with the device is common in other medical devices, so they believe the results will be positive.

The other area they will analyze is where it would be best to affix the very small device in the eye. One idea would be to piggyback it to an IOL.

“The advantage is that once an IOL is implanted, it’s very stable,” Dr. Sretavan said.

A second possibility would be to hook it on to the iris tissue, a concept used successfully with iris fixation devices that are actually larger than their sensor.

Either way, the placement would be in a part of eye that would not be cosmetically intrusive.

“We’ve focused until now on making the initial sensor and improving its performance. Now, the project needs to go in many directions to facilitate development,” Dr. Sretevan said.

Hyuck Choo, PhD

E: hchoo@caltech.edu

David Sretavan, MD, PhD

E: SretavanD@vision.ucsf.edu

Drs. Choo and Sretavan have no financial interests related to their comments.

This article is adapted from a presentation by Dr. Choo and Dr. Sretavan at the 2014 meeting of the Association for Research in Vision and Ophthalmology.