Saccadic eye movements differentiate functional cognitive disorder from mild cognitive impairment

Functional Cognitive Disorder ("FCD") is a type of Functional Neurological Disorder characterised by subjective cognitive complaints not fully attributable to brain injury, disease, or other neuropathological or psychiatric conditions. FCD is a cognitive impairment but does not necessarily "convert" to cognitive decline. However, FCD is common in Memory Clinics worldwide, and currently there is a lack of tests to objectively assess FCD. Establishing whether memory complaints are functional or not is vital for clinicians and objective tests are required. Previous research indicates that early-stage Alzheimer's disease can be differentiated from healthy individuals by antisaccade eye-movement. Therefore, eye movements may be able to objectively ascertain whether self-reported memory complaints are functional in nature. In this study, FCD participants were Memory Clinic patients who self-reported memory complaints but showed internal inconsistency regarding memory issues on memory tests. Participants with FCD were compared to Mild Cognitive Impairment (MCI) patients and healthy controls (HC) on antisaccadic and prosaccade eye movement tasks. The parameters obtained were reaction-time (RT) mean and SD and antisaccade error rate. MCI differed significantly from HC in antisaccade RT-mean, RT-SD, error-rate, and from FCD antisaccade RT-mean, RT-SD, and error-rate. FCD did not differ significantly from HC for antisaccade parameters. However, FCD differed significantly from HC for prosaccade RT-mean and RT-SD. MCI did not differ significantly from HC or FCD in prosaccade parameters. These results indicate that eye movement tasks could ultimately aid clinicians in the diagnosis of FCD. With additional research into sensitivity and specificity, eye movement tasks could become an important feature of memory clinics.