A microscale optical implant for continuous in vivo monitoring of intraocular pressure

Abstract

Intraocular pressure (IOP) is a key clinical parameter in glaucoma management. However, despite the potential utility of daily measurements of IOP in the context of disease management, the necessary tools are currently lacking, and IOP is typically measured only a few times a year. Here we report on a microscale implantable sensor that could provide convenient, accurate, ondemand IOP monitoring in the home environment. When excited by broadband near-infrared (NIR) light from a tungsten bulb, the sensor's optical cavity reflects a pressure-dependent resonance signature that can be converted to IOP. NIR light is minimally absorbed by tissue and is not perceived visually. The sensor's nanodot-enhanced cavity allows for a 3-5 cm readout distance with an average accuracy of 0.29 mm Hg over the range of 0-40 mm Hg. Sensors were mounted onto intraocular lenses or silicone haptics and secured inside the anterior chamber in New Zealand white rabbits. Implanted sensors provided continuous in vivo tracking of short-term transient IOP elevations and provided continuous measurements of IOP for up to 4.5 months.

Multifunctional biophotonic nanostructures inspired by the longtail glasswing butterfly for medical devices

“…1j). This scattering property could ameliorate the difficulty of detecting optical signals at wide angles, a commonly observed challenge among many light-based devices 14 such as implantable IOP sensors 15 (See Supplementary Section SI1 and Fig. S3–S4 for more details on the biological significance of the multifunctional transparency and its dual nano-structural basis present on C. faunus wings.…”

“…To demonstrate a medical application of multifunctional nanostructures, we used the nanostructured Si 3 N 4 -membrane as an opto-mechanical sensing element in a microscale implantable IOP sensor, which is a hermetically-sealed, pressure-sensitive, Fabry-Perot (FP) resonator 15 . A flat-surfaced or nanostructured flexible Si 3 N 4 -membrane forms the top surface of the FP-resonator while a mirror-like rigid Si forms the bottom surface.…”

“…In in vivo testing, FP-based IOP sensors suffer from narrow readout angles that severely limits sensor practical usability (Supplementary Fig. S20) and biofouling that shortens sensor lifespan 15 .…”

“…The angle independence enhanced by the nanostructure integration improved the stability and accuracy of the optical measurements against potential error sources such as respiratory movements, subtle eye motions, and detector misalignment. Furthermore, indirect IOP measurement techniques such as tonometry are influenced by various factors such as corneal thickness, curvature and biomechanics and are in general more error-prone compared to direct IOP measurement techniques such as implantable sensors 15,47 .…”

“…Herein, we seek inspiration from the multifunctional biophotonic nanostructures found on the transparent wings of the longtail glasswing ( Chorinea faunus ) butterfly to advance the versatility of micro-optical implants whose practical use is often limited by the angle dependency of sensing and readout processes 14,15 as well as short- and long-term biofouling 15–17 . We characterised in detail the surface and optical properties of the short-range-ordered nanostructures found on the C. faunus butterfly wings that could overcome the shortcomings of micro-optical implants.…”