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Abstract:
Purpose: Impaired pupillary light response (PLR) and decreased cerebrovascular reactivity (CVR) have been linked with neurodegenerative diseases, including Alzheimer’s disease. Here, we compare the PLR in response to different light stimuli with CVR measurements retrieved with transcranial doppler ultrasound (TCD), in order to determine if there is a relationship between CVR and PLR in healthy subjects.
Methods: 11 healthy subjects (sex: 5F; mean age=33±9 years) were studied. PLR data were acquired with PyPlr, an open-source system of hardware and software developed in-house (Martin et al., 2021). All subjects underwent a 2-minute dark adaptation before completing two PLR protocols. The first protocol was a 1 s (50 µW) white flash, with a 90 s interstimulus interval (ISI), to assess the PLR. The second was a 1 s blue flash (470 nm peak) followed by a 90 s ISI, then a 1 s red flash (659 nm peak, intensity matched to blue stimulus) followed by a 90 s ISI, to assess the post-illumination pupil response (PIPR) at maximal and minimal melanopsin sensitivity. Three trials were administered for each protocol. CVR measurements were retrieved from blood flow changes in the middle cerebral artery, obtained with transcranial Doppler ultrasound during a gas challenge (2 minutes of medical air, followed by 3 minutes of 5% CO2). All measurements were taken between 9:00 and 16:00.
Results: Although there were no statistically significant relationships between the PLR or PIPR and CVR, constriction velocity (p=0.09) and maximum constriction velocity (p=0.07) in response to white light showed positive trends with CVR. Additionally, the difference in percent change from baseline 6 s after light offset (6 s PIPR) between the red and blue light showed a weak negative trend with CVR (p=0.17).
Conclusions: This is the first work investigating the relationship between the PLR, PIPR, and CVR in healthy subjects. No statistically significant relationships were identified in the group between the PLR or PIPR and CVR, although some showed trends approaching significance. More research should be conducted in a larger, more diverse subject group to investigate the impact of other variables such as demographics or genetics, and the relationship between the PLR, PIPR, and CVR.
