Vertigo is a common disease, however the cause is very complex and wide-ranged. So, high knowledge and skills are indispensable to diagnose vertigo accurately. Based on these backgrounds, this study aims at developing simple method for diagnosing vertigo, which analyzes nystagmus by image processing. The algorithm for analyzing nystagmus can be divided into three stages: 1. Detect pupil, 2. Extract iris pattern, 3. Calculate rotation angle of torsional nystagmus by phase only correlation. By this proposal method, we succeeded to track three-dimensional eye movement.