Retinal mid-peripheral capillary free zones are enlarged in cognitively unimpaired older adults at high risk for Alzheimer's disease

BACKGROUND

Compared to standard neuro-diagnostic techniques, retinal biomarkers provide a probable low-cost and non-invasive alternative for early Alzheimer's disease (AD) risk screening. We have previously quantified the periarteriole and perivenule capillary free zones (mid-peripheral CFZs) in cognitively unimpaired (CU) young and older adults as novel metrics of retinal tissue oxygenation. There is a breakdown of the inner retinal blood barrier, pericyte loss, and capillary non-perfusion or dropout in AD leading to potential enlargement of the mid-peripheral CFZs. We hypothesized the mid-peripheral CFZs will be enlarged in CU older adults at high risk for AD compared to low-risk individuals.

METHODS

20 × 20° optical coherence tomography angiography images consisting of 512 b-scans, 512 A-scans per b-scan, 12-µm spacing between b-scans, and 5 frames averaged per each b-scan location of the central fovea and of paired major arterioles and venules with their surrounding capillaries inferior to the fovea of 57 eyes of 37 CU low-risk (mean age: 66 years) and 50 eyes of 38 CU high-risk older adults (mean age: 64 years; p = 0.24) were involved in this study. High-risk participants were defined as having at least one APOE e4 allele and a positive first-degree family history of AD while low-risk participants had neither of the two criteria. All participants had Montreal Cognitive Assessment scores ≥ 26. The mid-peripheral CFZs were computed in MATLAB and compared between the two groups.

RESULTS

The periarteriole CFZ of the high-risk group (75.8 ± 9.19 µm) was significantly larger than that of the low-risk group (71.3 ± 7.07 µm), p = 0.005, Cohen's d = 0.55. The perivenule CFZ of the high-risk group (60.4 ± 8.55 µm) was also significantly larger than that of the low-risk group (57.3 ± 6.40 µm), p = 0.034, Cohen's d = 0.42. There were no significant differences in foveal avascular zone (FAZ) size, FAZ effective diameter, and vessel density between the two groups, all p > 0.05.

CONCLUSIONS

Our results show larger mid-peripheral CFZs in CU older adults at high risk for AD, with the potential for the periarteriole CFZ to serve as a novel retinal vascular biomarker for early AD risk detection.

Remote and in-clinic digital cognitive screening tools outperform the MoCA to distinguish cerebral amyloid status among cognitively healthy older adults

INTRODUCTION

We evaluated the accuracy of remote and in-person digital tests to distinguish between older adults with and without AD pathological change and used the Montreal Cognitive Assessment (MoCA) as a comparison test.

METHODS

Participants were 69 cognitively normal older adults with known beta-amyloid (Aβ) PET status. Participants completed smartphone-based assessments 3×/day for 8 days, followed by TabCAT tasks, DCTclock™, and MoCA at an in-person study visit. We calculated the area under the curve (AUC) to compare task accuracies to distinguish Aβ status.

RESULTS

Average performance on the episodic memory (Prices) smartphone task showed the highest accuracy (AUC = 0.77) to distinguish Aβ status. On in-person measures, accuracy to distinguish Aβ status was greatest for the TabCAT Favorites task (AUC = 0.76), relative to the DCTclockTM (AUC = 0.73) and MoCA (AUC = 0.74).

DISCUSSION

Although further validation is needed, our results suggest that several digital assessments may be suitable for more widespread cognitive screening application.

A highly feasible, reliable, and fully remote protocol for mobile app-based cognitive assessment in cognitively healthy older adults

Introduction

The early detection of cognitive impairment is one of the most important challenges in Alzheimer's disease (AD) research. The use of brief, short-term repeated test sessions via mobile app has demonstrated similar or better reliability and validity compared to standard in-clinic assessments in adult samples. The present study examined adherence, acceptability, and reliability for a remote, app-based cognitive screening protocol in healthy older adults.

Methods

Cognitively unimpaired older adults (N = 52, ages 60-80) completed three brief cognitive testing sessions per day within morning, afternoon, and evening time windows, for 8 consecutive days using a mobile app-based cognitive testing platform. Cognitive tasks assessed visual working memory, processing speed, and episodic memory.

Results

Participants completed an average of 93% (M = 22.3 sessions, standard deviation = 10.2) of the 24 assigned sessions within 8 to 9 days. Average daily adherence ranged from 95% of sessions completed on day 2 to 88% of sessions completed on day 8. There was a statistically significant effect of session time on adherence between the morning and afternoon sessions only F (1, 51) = 9.15, P  = .004, η _p  ²   = 0.152, with fewer afternoon sessions completed on average. The within-person reliabilities of average scores, aggregated across all 24 sessions, were exceptionally high, ranging from 0.89 to 0.97. Performance on the episodic memory task was positively and significantly associated with total score and word list recall score on the Telephone Interview for Cognitive Status. In an exit survey, 65% of participants reported that they "definitely" would complete the sessions again.

Discussion

These findings suggests that remote, mobile app-based cognitive testing in short bursts is both highly feasible and reliable in a motivated sample of cognitively normal older adults. Limitations include the limited diversity and generalizability of the sample; this was a largely White, highly educated, and motivated sample self-selected for AD research.