Contact lens with stretchable distributed-feedback laser for intraocular pressure monitoring

Abstract

Continuous monitoring of intraocular pressure (IOP) is essential for the diagnosis and management of glaucoma, yet existing clinical methods rely on intermittent in-clinic measurements that miss critical diurnal fluctuations. Smart contact lenses are an attractive platform for continuous IOP tracking, and optical strain sensors are particularly promising thanks to their high sensitivity and natural readout. Most such optical sensors infer strain from the period of a regular structure - a grating or photonic crystal - whose deformation is read out optically. However, the precision of all sensors based on the period of regular structures is fundamentally bounded by the uncertainty principle, which severely limits performance at the millimeter length scales available inside a contact lens. Here, we address this limitation by integrating a distributed-feedback (DFB) laser, based on a surface-modulated ultrathin F8BT dye layer, into a soft polydimethylsiloxane (PDMS) contact lens. Operating at a symmetry-protected bound state in the continuum at the Γ point, the device produces a narrow lasing line whose wavelength shifts directly with grating strain - a quantity not constrained by the spatial uncertainty principle. The DFB structure is fabricated by UV holographic lithography and transferred onto the lens by a simple float-off process, yielding a stretchable, transparent, polymer-compatible sensor that is intrinsically scalable. Tested on a custom artificial eye model whose pressure-induced deformation is comparable in scale to that reported for the human eye, the sensor achieves a sensitivity of 0.027 nm/mmHg and a calibration residual of 1.2 mmHg under phantom conditions, a level relevant to tonometric monitoring, with substantial headroom currently limited mainly by auxiliary readout equipment.