Chromatic Pupillometry in Isolated Rapid Eye Movement Sleep Behavior Disorder

Area of Science:

• Neuroscience
• Ophthalmology
• Sleep Medicine

Background:

• Melanopsin retinal ganglion cell (mRGC)-mediated pupillary light reflex (PLR) abnormalities are observed in neurodegenerative diseases like Parkinson's.
• Isolated rapid eye movement (REM) sleep behavior disorder (iRBD) is a significant prodromal risk factor for α-synucleinopathies.

Purpose of the Study:

• To quantitatively compare PLR and mRGC-mediated contributions in iRBD patients versus healthy controls.
• To investigate the correlation of PLR metrics with clinical variables and biomarkers in iRBD.

Main Methods:

• 16 iRBD patients and 16 healthy controls underwent neuro-ophthalmological evaluation and chromatic pupillometry.
• PLR metrics were correlated with REM atonia index (RAI), DaTscan, and skin biopsy for phosphorylated-α-synuclein (p-α-syn).

Main Results:

• iRBD patients exhibited higher baseline pupil diameter and reduced rod-transient PLR amplitude compared to controls.
• PLR rod-contribution correlated with RAI, and reduced PLR amplitude was linked to p-α-syn deposition in skin biopsies.

Conclusions:

• Pupillary light reflex abnormalities in iRBD may serve as potential biomarkers.
• These findings could aid in the risk stratification for phenoconversion in iRBD patients.