Pupillary light response changes in patients with Mild Cognitive Impairment

Abstract

Purpose : Mild cognitive impairment (MCI) is associated with an increased risk of developing dementia, which is considered prodromal to Alzheimer's disease (AD). Previous studies reported retina nerve fiber layer (RNFL) thickness and circadian system alterations in patients with MCI. Since a decreased number of intrinsically photosensitive retinal ganglion cells – ipRGCs, which mediate circadian rhythm, is correlated to the reduction of RNFL thickness in glaucoma patients, we hypothesized that ipRGCs may be affected in MCI. So, our objective was evaluate the cone, rod and ipRGC contributions to the pupillary light response (PLR) in patients with MCI compared to a control group.

Methods : Patients with MCI were diagnosed at The Laboratory of Psychiatric Neuroimaging (LIM21) and underwent a complete ophthalmological examination in the Psychophysics and Clinical Electrophysiology of Vision Laboratory at University of São Paulo. Medical conditions such as disabling chronic diseases, psychiatric disorders, ophthalmological diseases were exclusion criteria. The PLR was evaluated using a Ganzfeld (Q450, Roland), controlled by the RETI–port system (Roland Consult, Brandenburg, Germany). The stimuli consisted of 1s blue (470 nm) and red (640 nm) light flashes alternately. To assess the contribution of the different photoreceptor types we used 640 nm flashes at 2 log cd/m² for cones, 470 nm at -3 log cd/m2 for rods and 2 log cd/m² for ipRGCs

Results : We present the preliminary results obtained from six patients with MCI (75.33 yrs ± 6.74) and five controls (62.80 yrs ± 10.59; p=0.52). We found an abnormality of cone and rod contribution in the MCI group. With the red stimulation, the time to reach the peak amplitude (PA) was shorter in MCI than in the control group (p=0.03). The same was observed with -3 log cd/m for blue stimulation (p=0.03). In relation with the ipRGCs (blue stimulation), we noticed a similar time decrease to reach the PA (p=0.02). In addiction, the normalized median constriction amplitude of the pupillary sustained response (SR) of the PLR between 6 and 8 s after light offset was smaller in MCI than for the control group (p=0.03).

Conclusions : Our results suggest that cones, rods and ipRGCs contributions to PLR are affected in patients with MCI. Further studies might increase the number of subjects evaluated to observe if the results would be replicated in a larger population.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.