Test‐retest validity of light reflex pupillometry in a memory clinic cohort

Abstract

AbstractBackgroundThe pupillary light reflex and the contributing cerebral functions can be objectively assessed using a pupillometer. Light reflex pupillometry (LRP) has been found to be altered in Alzheimer’s disease (AD) and has potential as a diagnostic aid in this disease as a novel biomarker. Little is known about the variability of LRP in patients seen in memory clinics (including patients with AD). We aimed to quantify the test‐retest validity of LRP in these patients to elucidate possible pitfalls in using pupillometry and to ascertain the feasibility of implementing this clinical tool in a memory clinic setting.MethodIn total, 50 patients under diagnostic evaluation in a tertiary memory clinic will be included in the present study. Patients suspected of a neurodegenerative disease are included on the day of a scheduled lumbar puncture (LP). We measure the LRP at baseline (day of LP), 3‐14 days after LP, and 21‐35 days post‐LP using a research grade pupillometer (PLR‐3000, NeurOptics®). Spaghettiograms of measurements will be presented and the intraclass correlation coefficient from a two‐way mixed effects model will be calculated for the eight pupillometric variables provided by the PLR‐3000: Baseline pupil diameter, peak constriction diameter, change in pupillary size, average and maximum constriction velocity, average dilation velocity and T75 (time to reach 75% of baseline pupil diameter after peak constriction). We will study possible influencing factors that could affect the test‐retest variability by studying subgroups of patients based on diagnosis, disease severity, cerebrospinal fluid Aβ‐42, concurrent eye disease and medication.ResultAs of January 2023, 24 patients (9 female) have completed follow‐up. The mean age of patients is 72 years (range 63‐79). Half of the patients were diagnosed with Alzheimer’s disease (MCI or mild dementia). Our preliminary results show moderate‐good test‐retest reliability of most pupillometric variables.ConclusionLight reflex pupillometry may be a promising new bedside biomarker for AD. The present study generally demonstrated a moderate‐good test‐retest reliability of LRP in a memory clinic population. The study contributes to the foundation for an exploration of the tool for diagnostic purposes in various diseases, including Alzheimer’s disease.