A recent study published in npj Flexible Electronics proposed an innovative design for a smart contact lens designed to provide daily, real-time intraocular pressure (IOP) monitoring and tested its efficacy in animal models.
Give me some background on smart contact lenses.
Smart contact lenses with sensors that measure IOP by capturing internal ocular changes have recently gained attention as a promising approach to address the need for continuous IOP monitoring to effectively treat early-stage glaucoma.
- Note: The principle behind this technology is to sense deformation in the contact lens caused by elevated IOP, which changes the curvature radius of the cornea.
And what does the current landscape look like?
Current sensor technologies include microfluidic, optical, and wireless systems. The first two rely on changes in fluid flow in microfluidic channels integrated into the contact lens and the principle of light reflection, mainly observed by the naked eye or camera, respectively.
However: The study authors explained that these approaches have low sensitivity and significant errors; additionally, they face limitations in dark environments.
- Conversely: Wireless systems have the potential for practical monitoring via continuous information transmission to a receiving antenna or device.
How does this new smart contact lens work?
The contact lens design is based on a transparent resistive pressure sensor consisting of a 70 MHz double-loop gold antenna and a ring-shaped multilayer pressure sensor.
- This is composed of a Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) (PEDOT: PSS) film—noted for its good light transmittance that minimizes interference with the user’s vision.
In addition: The researchers designed a multilayer sandwich structure as the resistive sensor, including a highly sensitive PEDOT:PSS layer and a PEDOT: PSS/Polyvinyl alcohol (PVA) layer to improve stretchability.
And the intended result?
As such: When the IOP increases and causes the sensor to stretch, this highly sensitive PEDOT:PSS layer cracks, causing a change in resistance.
Plus: The researchers introduced the idea of parity-time (P-T) symmetry into the antenna at the detector side to improve the Q-factor of the magnetic resonance coupling system to:
- Improve the energy transfer efficiency of the coupled oscillators
- Enable high-sensitivity wireless measurements
Back up … what is P-T symmetry?
P-T symmetry has emerged as a key concept in quantum mechanics, with significant implications in optics and photonics, particularly in areas such as waveguides, microresonators, and lasers.
What you need to know: The controllable manipulation of gain and loss in PT-symmetric systems has opened up new possibilities for advanced signal processing, communication technologies, and optical devices.
Alrighty, now let’s move on to the study.
This study encompassed multiple steps, including the fabrication of the smart contact lens and
testing of sensor resistance and IOP monitoring in three tests:
- A polydimethylsiloxane (PDMS) eye model
- In vitro testing on porcine eyes
- In vivo testing on rabbit eyes modified via microbead injection
Moreover: The research team assessed ocular cell viability with the PEDOT:PSS sensor by placing it in a culture dish containing human corneal endothelial (HCE) cells to determine cell survival.
Findings?
Investigators achieved a sensitivity of 47.31 Ω/mmHg with the smart contact lens design—approximately 15 times higher than a conventional approach, corresponding to a resistance change 183 times larger.
- Note: Q= f0/▵f, with f0 being the resonant frequency (in hertz) and ▵f is the bandwidth or full-width at half maximum of the peak (in hertz).
Anything else?
Both in vitro and in vivo wireless IOP measurements, using a commercial tonometer and a fabricated sensor lens, showed a strong correlation with R2 values of 95% and 97%, respectively.
Moreover: The contact lens sensor demonstrated biocompatibility, confirming its safety for use in biological systems.
Expert opinion?
The study authors noted that this study highlights how the PEDOT:PSS/PVA resistive sensor possessed three key attributes:
- High sensitivity: Ensuring that IOP changes are effectively transmitted through the P-T wireless transmission system.
- Recoverability: Enabling the sensor to regain its original state following deformation, facilitating continuous and reliable IOP measurements.
- High transmittance: Ensuring that normal vision remains largely unaffected during the measurement process.
“By integrating these three characteristics, the sensor allows for continuous monitoring of IOP fluctuations with minimal disruption to the patient’s daily life, thereby providing a comprehensive record of IOP variations,” they added.
Take home.
These findings demonstrate the potential for long-term, non-invasive IOP monitoring with a novel smart contact lens design to allow for early diagnosis and treatment of glaucoma.