Smart Contact Lens for Precise Eye Tracking

By Dr Silpaja Chandrasekar, PhDMay 8 2024Reviewed by Susha Cheriyedath, M.Sc.

In a paper published in the journal Nature Communications, a groundbreaking advancement in human-machine interaction (HMI) was introduced: a miniature, imperceptible smart contact lens for eye tracking and wireless interaction. Using a frequency encoding strategy, this chip-free, battery-free lens detected eye movements with exceptional accuracy, surpassing the central fovea's precision. Applications ranged from eye-drawing to camera control, with comprehensive biocompatibility tests confirming its safety. This innovation heralded a new era in eye-tracking technology and HMI.

Related Work

In previous research, wearable, flexible devices revolutionized HMI, offering functions like haptic sensing, speech recognition, gesture recognition, and motion capture. However, existing eye-tracking methods faced limitations, prompting the development of miniaturized smart contact lenses (SCL).

SCLs provided augmented reality capabilities and medical monitoring functionalities but faced challenges compared to traditional scleral coil-based eye tracking technology due to their wired nature and bulky measurement systems. A need arose for imperceptible eye-tracking devices to advance applications across various fields.

a Schematic illustration of eye-machine interaction like screen handling when appreciating Vincent van Gogh’s famous artwork The Starry Night and robot control by eye tracking and eye command emission using SCL. Adapted under terms of the CC-BY license. Copyright 2024, Canino3d, Sketchfab, Inc⁶⁷. b Photograph of SCL. c Schematic illustration of materials and structures of SCL. d Long-term hydrophilia test of SCL. Data are presented as mean with standard deviation of n  =  5 independent samples. e Photographs of SCL under normal, compression, and stretching status. f Long-term cytotoxicity test of SCL using human corneal cell lines. Data are presented as mean with standard deviation of n  =  6 independent cells. g Fluorescence images of HCE-T incubated in different extracts. h Quantified accumulation of proteins on the bare commercial contact lens (orange column) and the SCL (fuchsia column) after biperiodic protein accumulation and disinfection using unpaired two-tailed Student’s t test. p  =  0.0195 before vs. after first disinfecting the bare commercial contact lens, n  =  3; p  =  0.00191 before vs. after first disinfecting the SCL, n  =  3; p  =  0.0167 after first disinfecting the bare commercial contact lens vs. the SCL, n  =  3; p  =  0.0288 before vs. after second disinfecting the bare commercial contact lens, n  =  3; p  =  0.000276 before vs. after second disinfecting the SCL, n  =  3; p  =  0.0000159 after second disinfecting the bare commercial contact lens vs. the SCL, n  =  3. Data are presented as mean with standard deviation of n  =  3 independent samples. Significant difference was set at ***p < 0.001, **p < 0.01, and *p < 0.05.

SCL Development Process

The eye-tracking SCL preparation process involved three main procedures: preparing flexible tags, encapsulation using medical elastomer, and hydrophilic treatment. Flexible tags were fabricated by spin-coating polyimide layers, patterning, and electroplating to achieve the desired thickness. Laser cutting defined the tag patterns, and researchers encapsulated them in medical-grade silicone elastomer. Analysts then applied subsequent hydrophilic treatment to enhance surface properties.

Cytotoxicity tests were conducted using human corneal epithelial cell lines to assess the safety of the SCL. Cells were plated and incubated with extracts from silicone-embedded tags and bare commercial contact lenses. Cell viability was measured using a cell counting kit and fluorescent imaging techniques, with comparisons made against control groups.

Eye calligraphy and painting experiments were performed using a laboratory virtual instrument engineering workbench (LabVIEW) program and a 2D eye movement model. Calibration was conducted using a swirling pattern, and eye movements were tracked to determine accuracy. Eye-machine interaction experiments included controlling a Gluttonous Snake game, webpage navigation, and a pan-tilt-zoom (PTZ) camera using eye commands. The feasibility and accuracy of these interactions were evaluated.

The team conducted biocompatibility tests using in vivo rabbit models. The rabbits wore SCLs on their eyes for various durations, and researchers performed ophthalmic examinations to assess biocompatibility—histopathological analysis of collected tissues provided further insights into the safety profile of the SCLs during extended wear.

These methodologies comprehensively addressed the fabrication, safety assessment, functionality testing, and biocompatibility evaluation of the eye-tracking SCL, laying the groundwork for its potential applications in diverse fields.

Revolutionizing HMI

The eye-tracking SCL offers a revolutionary interface between humans and machines, enabling real-time interaction through eye movements. With the ability to detect gaze direction, the SCL facilitates tasks such as screen navigation and robot control. Equipped with miniaturized radio frequency (RF) tags embedded in its periphery, the SCL detects eye motion signals, allowing for seamless integration with software and hardware systems.

The SCL is constructed using medical-grade silicone elastomer, ensuring biocompatibility and comfort during wear. Hydrophilic surface treatment enhances long-term wearability, while a commercial contact lens layer adds an extra safety measure. Physicochemical characterizations confirm optical transparency, flexibility, and cytotoxicity levels within safe limits, ensuring user comfort and safety.

Powered by an innovative time-sequential eye-tracking algorithm, the SCL offers unparalleled precision in eye-controlled tasks such as calligraphy and painting. A swirling calibration method optimizes accuracy, allowing for high-definition eye movements and minimizing errors. The SCL's versatility accommodates variations in corneal curvature, ensuring accurate individual performance. Additionally, the SCL's tolerance to environmental factors like light interference and slippage further enhances its usability and reliability.

In vivo tests on rabbit models validate the functionality and safety of the SCL, demonstrating its ability to control external devices wirelessly and its biocompatibility over extended wear periods. The absence of adverse effects in ocular evaluations underscores the SCL's suitability for real-world applications. Overall, the eye-tracking SCL represents a significant advancement in human-machine interaction, offering seamless control and enhanced user experience across various domains.

Summary

In conclusion, the eye-tracking SCL revolutionized human-machine interaction by enabling real-time control through eye movements. Equipped with miniaturized RF tags, it seamlessly integrated with software and hardware systems, offering precision and versatility.

Constructed with biocompatible materials and validated through in vivo tests, the SCL ensured comfort and safety during extended wear. Its innovative time-sequential eye-tracking algorithm and swirling calibration method provided unparalleled accuracy in tasks like calligraphy and painting. Overall, the SCL represented a significant advancement in user experience across various domains.