Research on Accessible Digital Musical Instruments (ADMIs) has received growing attention over the past decades, carving out an increasingly large space in the literature. Despite the recent publication of state-of-the-art review works, there are still few systematic studies on ADMIs design analysis. In this paper we propose a formal tool to explore the main design aspects of ADMIs based on Dimension Space Analysis, a well established methodology in the NIME literature which allows to generate an effective visual representation of the design space. We therefore propose a set of relevant dimensions, which are based both on categories proposed in recent works in the research context, and on original contributions. We then proceed to demonstrate its applicability by selecting a set of relevant case studies, and analyzing a sample set of ADMIs found in the literature.