Patients suffering from Alzheimer's Dementia (AD) have increasing difficulties to orient in space and often fail to recognize basic realities and even their closest relatives. These symptoms lead to severe deterioration of everyday life and finally to total dependence. In this report we present the case of Carolus Horn, a famous german artist, who contracted with AD. The qualitative and quantitative analysis of changes in his artwork during disease progression gives an impressive insight into the patient's visual world and how it becomes increasingly affected by delusional misperceptions, spatial errors and changes of colour-perception in the course of disease. Carolus Horn's artwork lets us see the world through the patient's eyes and by that it helps us to better understand the consequences of visuospatial and cognitive changes in AD.