The VIVA study is focused on Alzheimer's disease patients with a low vision due to a bilateral cataract. The aim is to study cataract surgery results on patients' autonomy, behaviour, and mood. In fact those dement elderly patients suffer from a progressive loss of superior functions, with loss of autonomy, behaviour and mood degradation, associated with physical disabilities. The work hypothesis is that a loss of sensorial functions, particularly visual, is an aggravating factor of NEURO-cognitive troubles and absence of communication with outside circle. The protocol consists in investigating superior functions, autonomy, and behaviour troubles of the participating patients, with the help of a series of neuropsychological tests used one month before and three months after cataract operation on the eye with the worst vision. Independently of the study, patients must have given an informed consent to cataract surgery. Their participation lasts 4 months+/- 1 month. The aim of the study is to evaluate whether the cataract surgery improves patients' behaviour, autonomy and mood and possibly to show evidence onf drawbacks in of such a practice.The main objective targets to cataract surgery benefice on patients suffering from both Alzheimer's disease and impeding cataract, aiming to improve behaviour troubles. The specific objective is to measure this benefice in correlation with visual acuity improvement.