User interfaces are important for streamlining the interactions between humans and computers. However, there are few effective approaches for collecting users' preferences implicitly and objectively for the purpose of user interface (UI) design optimization. This paper presents an effective approach to interactive genetic algorithm (IGA) optimization-based UI design via eye tracking, including eye-movement data based users' preference inferring, gene coding for real UI components and design features, and the visualization and interaction mechanisms. Then we design and build a prototype system that applies IGA to generate and optimize music player UI solutions automatically. An evaluation of our prototype system suggests that it can generate and identify personalized UI designs reliably with minimal user intervention and high efficiency and user satisfaction.