The diploma thesis provides the reader theoretical knowledge of the current state of digital realities (virtual, augmented and mixed reality) and explains their differences. It deals with the most common anxiety disorders, which are phobias. It focuses on the category of specific phobias, specifically arachnophobia, which is as intense fear of spiders. Further it studies existing methods of the treatment of specific phobias with focus on the virtual reality exposure therapy as an innovative method of the treatment. The aim of the practical part of the thesis was to design and create an interactive virtual reality application for the HTC Vive platform, which would serve as treatment of chosen phobia, in our case the arachnophobia. The individual chapters guide the reader through all phases of the software development cycle, from collecting requirements to testing and subsequent feedback from the psychotherapist and the potential patients. An essential part is devoted to the detailed procedure in the implementation of the solution, which includes samples of pictures, tables and source codes. Part of this work is a complete project of virtual reality application and also evaluation of research, which was realized by the form of electronic questionnaire.