Development of the Snellen Memory Test (SMT): An episodic memory test to screen for AD risk in a clinical optometry/ophthalmology setting

Abstract

AbstractBackgroundAlthough we have been working to discover and validate retinal imaging biomarkers for preclinical AD risk, the cognitive assessment of episodic memory function remains the most commonly relied on screening approach. Here, we sought to develop a brief screening test for episodic memory, to augment retinal biomarkers in the early detection of AD. By relying on the standard Snellen Eye Chart as the stimulus field, we aim to create an instrument that can be seamlessly incorporated into standard clinical optometry/ophthalmology practices. This pilot study sought to identify episodic memory questions of equivalent difficulty, based on the Snellen Eye Chart, that can eventually be scored using a mobile application.Method12 cognitively normal (CN) older adults (24‐56 years) completed the SMT, consisting of 2 x 11 question forms, with both free‐ and cued‐recall components: one form immediately after encoding and one form after a 20‐minute delay. Item analysis was performed for each test question at immediate and delayed recall, and the mean difficulty index (DI) of all questions was computed along with a 95% confidence interval (CI).ResultThe mean DI for all questions at immediate recall was 0.66 (95% CI: 0.53‐0.79) with two questions falling below the 95% CI lower bound (0.53). The mean DI at delayed recall was 0.70, (95% CI: 0.57, 0.82) with one question falling below and one falling above the 95% CI upper bound. We eliminated 4 questions, leaving a pool of 18 questions of equivalent difficulty at immediate and delayed recall.ConclusionMany of the items for the SMT were moderately difficult for CN individuals. These questions may be further developed to screen for AD risk in CN older adults in a clinical setting. We are currently collecting data in a cohort (N=100) of CN older adults (55‐80) at both low‐ and high‐risk for preclinical AD, which will be used to further refine this novel memory test. Our next step is to validate the SMT against gold standard neuropsychological assessments of episodic memory, and to examine the added prognostic value of this test in conjunction with our panel of retinal imaging AD risk biomarkers.