Cerebral visual impairment (CVI) is the leading cause of visual impairment in developed countries. No treatment for CVI exists and children need long-term individualized therapy. In this paper we describe a serious game with dynamic difficulty adjustment (DDA) developed for children with CVI. The DDA is realized with Reinforcement Learning. Currently a double-blind Randomized Controlled Trial (RCT) is running, where children with CVI play this serious game.