Injectsense Real-Time Eye Pressure Monitoring

October 9, 2019 Clive Maxfield

Photo of Injectsense's prototype of wireless silicon sensor module next to a grain of rice and a quarter

A prototype of Injectsense's wireless silicon sensor module next to a grain of rice and a quarter (Image source: Injectsense)

A little over a year ago, I noticed that things sometimes got a little blurry while I was looking at my computer screen. My cousin Graham in England has macular degeneration, which has left him almost totally without sight. I have to admit that the thought this might happen to me was lurking in the back of my mind, so I set up an appointment with my ophthalmologist.

As opposed to having my eyes dilated, I opted to have photographs taken of my retina. The ophthalmologist informed me that I was looking good on the macular degeneration front, but that he was worried about the possibility of my exhibiting the early stages of glaucoma.

Thanks to the wonders of the internet, I now know more than I ever wanted to about glaucoma, including the fact that it's a condition that causes damage to the optic nerves in your eyes. Also, if untreated, it gets worse over time, and it's often linked to a buildup of pressure inside your eyes.

The pressure inside your eyes is referred to as intraocular eye pressure (IOP). The term tonometry refers to a test used to measure your IOP using an instrument called a tonometer. Such an instrument determines your IOP by measuring the resistance of your corneas to indentation (the ophthalmologist then adds "fiddle factors" based on things like the thickness of your corneas).

The ophthalmologist measured my IOP using a non-contact tonometry technique known as the air puff test, in which a small burst of air is puffed into your eye. The tonometer measures the air bouncing back from your eye to determine the IOP.

Although today's tonometers are state-of-the-art, the data they provide is really only relevant at that particular moment in time. Unless the patient wishes to move into the ophthalmologist's office, and the ophthalmologist is amenable to taking readings throughout the day and night, there is no way to continuously track the IOP and relate it to things like environmental conditions, the patient's activity, and the way in which the glaucoma responds to various treatments, including drug regimens… or is there?

Introducing Injectsense

Earlier today, a new sensor-enabled digital health company called Injectsense left stealth mode to announce the completion of a successful in-vivo animal study of the first implantable wireless sensor and monitoring system designed to collect long-term IOP data.

Smaller than a grain of rice, the 2.5 mm x 0.6 mm hermetically sealed silicon device includes a MEMS pressure sensor and an ASIC. The prototype part is powered via external electromagnetic induction, but the next-generation device will include a solid-state battery, and subsequent generations may also boast energy harvesting capabilities.

Although is may sound a little scary, the sensor can be quickly and painlessly implanted in the eye. The self-anchoring mechanism (not shown in the above image) attaches to the outside of the eyeball and prevents the sensor from being fully subsumed into the eye, thereby facilitating easy retrieval at a later date if necessary (the long term goal is for the sensor to remain resident for years as required).

The device interfaces well with media (blood, tissue, other fluids) without interfering with the electronics that support the sensing, computing, and transmission of data. 

Remember that all that's being announced at this time is a successful week-long in-vivo animal study, but things look promising for human trials in the not-so-distant future. Since the sensor is so small, and in order to conserve power, data can only be wirelessly transmitted over a short distance. One potential usage scenario for the future will be to have an associated app loaded on a wearable device like an Apple Watch. The sensor can continuously gather and store data until the user brings his or her wrist close to their eye, at which time the sensor would upload its data to the watch, which would then pass the data to the cloud (possibly via another device like a smartphone or tablet).

The goal is to have an organ-to-cloud data connection that will provide unprecedented visibility into the IOP profile of the patient over time. The insights into previously unobserved changes that may affect glaucoma progression will enable clinicians to assess the effectiveness of alternative glaucoma therapies in real-time.  

And this is only the beginning, beyond ophthalmology, this type of sensor-enabled digital health platform is highly versatile, potentially enabling diagnostic and therapeutic applications in many different domains, from intracranial, urological, and various cardiovascular pressure parameters to neurosurgery and fluidic applications. We truly do live in exciting times.

 

About the Author

Clive Maxfield


Clive "Max" Maxfield received his BSc in Control Engineering in 1980 from Sheffield Hallam University, England and began his career as a designer of central processing units (CPUs) for mainframe computers. Over the years, Max has designed everything from silicon chips to circuit boards and from brainwave amplifiers to steampunk Prognostication Engines (don't ask). He has also been at the forefront of Electronic Design Automation (EDA) for more than 30 years.

Well-known throughout the embedded, electronics, semiconductor, and EDA industries, Max has presented papers at numerous technical conferences around the world, including North and South America, Europe, India, China, Korea, and Taiwan. He has given keynote presentations at the PCB West conference in the USA and the FPGA Forum in Norway. He's also been invited to give guest lectures at several universities in the US and at Oslo University in Norway. In 2001, Max "shared the stage" at a conference in Hawaii with former Speaker of the House, "Newt" Gingrich.

Max is the author of a number of books, including Designus Maximus Unleashed (banned in Alabama), Bebop to the Boolean Boogie (An Unconventional Guide to Electronics), EDA: Where Electronics Begins, FPGAs: Instant Access, and How Computers Do Math.

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