CAN EYETRACKING METRICS RELATE TO PERFORMANCE ON VISUAL COGNITIVE TESTS OF INDIVIDUALS WITH YOUNG-ONSET ALZHEIMER’S DISEASE?

Abstract

Eyetracking has been used to determine oculomotor impairments in individuals with Alzheimer's disease (AD) and other neurodegenerative conditions (Crawford et al., 2005; Boxer et al., 2012; Yang et al., 2013; Shakespeare et al., 2015). Phenotypic differences in eyetracking metrics have also been reported between typical AD and the clinicoradiological syndrome posterior cortical atrophy (PCA; Shakespeare et al., 2015). In this study, we explored the relationship between eyetracking metrics and standard visual cognitive tests in a phenotypically diverse cohort of patients with young onset dementia AD (YOAD), all with symptom onset before the age of 65 years. Fifty-seven participants were included: 36 individuals with YOAD (10 of whom also met criteria for PCA) and 21 age-matched healthy controls. Participants completed three eyetracking experiments: fixation, pro-saccade and smooth pursuit tasks (see Figure 1). Frequentist summary metrics were used as outcome measures and their relationship with aspects of cognitive function explored by looking at correlations with basic visual (shape discrimination), visuoperceptual (fragmented letters, object decision), visuospatial (dot counting, letter cancellation) and measures of single word recognition included in the cognitive tests. Consistent with previous findings, the small PCA subgroup showed more abnormalities in oculomotor characteristics compared to the remainder of the cohort for 4/7 eyetracking metrics (see Table 1). Across the whole YOAD cohort, the pro-saccade and smooth pursuit tasks showed moderate correlations with visuoperceptual and visuospatial test scores. Conversely, the measure for the fixation task showed no significant relationship to any visual cognitive task. Basic visual shape discrimination performance was only related to pro-saccade performance, whilst the spatial dot counting test alone associated with pro-saccade accuracy. The relatively simple and specific nature of eyetracking opens routes to sensitive, quantitative, repeatable evaluations not only of basic oculomotor function but also visuoperceptual and visuospatial processes and other domains of higher cognitive function in individuals with neurodegenerative disease. The current findings provide further insights into the complex relationship between aspects of visual processing and oculomotor function. Performance of a control and a patient with YOAD (PCA) in the different eyetracking tasks: light blue circles show fixations, orange arrows indicate saccades and red dots/crosses represent target position. Orange circles in the pro- saccade task outline the interest area (an area within two degrees of visual angle from the target position).