Pupillary Hippus as a Biomarker: Spectral Signatures and Complexity Approaches in Autonomic and Clinical Contexts

Area of Science:

• Neuroscience
• Physiology
• Ophthalmology

Background:

• Pupillary hippus, spontaneous pupil diameter oscillations, is a non-invasive indicator of autonomic and central nervous system activity.
• A unified framework linking hippus spectral features, physiological basis, and analytical complexity is currently lacking.
• Existing research highlights the potential of hippus but faces methodological heterogeneity.

Purpose of the Study:

• To synthesize spectral and nonlinear pupillometry studies on hippus.
• To propose a paradigm-aware taxonomy of hippus frequency bands.
• To integrate physiological underpinnings and analytical complexity for a coherent framework.

Main Methods:

• Narrative review of spectral and nonlinear pupillometry studies.
• Integration of evidence from autonomic tests and cognitive-arousal paradigms.
• Analysis of physiological metrics, spectral features, and complexity indices.

Main Results:

• Low-frequency hippus components correlate with respiratory and vasomotor rhythms.
• Higher-frequency fluctuations and complexity are sensitive to cognitive load, visual fatigue, and pathology.
• Glaucoma emerges as a promising translational model for hippus-based biomarkers.

Conclusions:

• A proposed taxonomy categorizes hippus frequency bands, linking them to physiological states.
• Hippus analysis shows clinical potential, particularly for glaucoma detection and monitoring.
• Methodological standardization and further validation are crucial for clinical adoption.