Oculomotor Testing in the Differential Diagnosis of Dementia

Dementia with Lewy bodies (DLB) is the second most common cause of neurodegenerative dementia. In its early stages, the differential diagnosis of DLB and Alzheimer's disease (AD) can be challenging. The differential diagnosis is particularly important given that patients with DLB respond well to cholinesterase inhibitors but show sensitivity to neuroleptic medications which are contraindicated in DLB. DLB tends to progress more quickly than Alzheimer's disease. Diagnostic accuracy may be improved. Oculomotor recording, easy to perform could be helpful in order to identify and reliably assess fluctuating attention performance in DLB patients. Main objective: \- to improve differential diagnosis between DLB and AD in the early stages of the disease with oculomotor measurements Secondary objectives: * to examine the association between the oculomotor records and neuropsychological examination assessing attention abilities and their fluctuations * to evaluate the benefit of complementary neuropsychological tests in the distinction between DLB and AD cases * to examine the relationship between hippocampal volume and neuropsychological examination in DLB cases * to examine the diagnostic performance of MRI (Support Vector Machine) between DLB and AD * to examine the interest of CSF alpha synuclein concentration to discriminate DLB from AD * to assess at one year variations in oculomotor test scores and neuropsychological test scores Method and design Longitudinal multicenter study including 100 patients with a DLB or AD diagnosis. Clinical examination at one year.