Polarizer-assisted pupillometry through closed eyelids, overcoming pupil position dependence

Area of Science:

• Biomedical Optics
• Ophthalmology
• Medical Imaging

Background:

• Accurate pupillometry is crucial for clinical and research applications.
• Current methods require open eyes, limiting use in sedated or sleeping patients.
• Short-wave infrared (SWIR) imaging offers noninvasive closed-eye pupillometry but faces challenges like eyelid glare and low signal-to-noise ratio (SNR).

Purpose of the Study:

• To enhance closed-eye pupillometry using polarization filters within SWIR imaging.
• To develop advanced algorithms for pupil localization and gaze estimation under natural closed-eye conditions.

Main Methods:

• Experiments utilized SWIR imaging with various polarizer configurations (parallel, crossed, no polarizers) on healthy volunteers.
• Pupillary light reflexes (PLR) were recorded under open and closed-eye conditions with different gaze directions.
• Image analysis involved brightness difference imaging and statistical modeling to assess signal quality and SNR.

Main Results:

• Crossed polarizers significantly improved closed-eye image quality by reducing eyelid glare compared to parallel or no polarizers.
• The crossed configuration achieved the highest PLR brightness change and SNR, enabling robust pupil localization across various gaze directions.
• Developed algorithms facilitated reliable PLR detection despite natural eyelid closure and gaze variations.

Conclusions:

• Integrating crossed polarizers into SWIR pupillometry substantially improves signal fidelity and pupil localization through closed eyelids.
• This method overcomes limitations of prior techniques, enabling accurate, touchless pupillometry in critical clinical scenarios.
• The advancements support applications in anesthesiology, sleep medicine, and neurocritical care.