This paper introduces a method to estimate gaze direction using images of the eye captured by a single high-sensitivity camera. The purpose is to develop wearable devices that enable intuitive eye-based interactions and applications. Indeed, camera-based solutions, as opposed to commercially available infrared-based ones, allow wearable devices to not only obtain natural user responses from eye movements, but also scene images reflected on the cornea, without the need for additional sensors. The proposed method relies on a model approach to evaluate the gaze direction and does not require a frontal camera to capture scene information, making it more socially acceptable if embedded in a glassesshaped device. Moreover, recent development in high-sensitivity camera sensors allows us to consider the proposed method even in low-light condition. Finally, experimental results using a prototype wearable device demonstrate the potential of the proposed method solely based on cornea images captured from a single camera.