Brightness adaptation is a fundamental ability in human visual system, and adjusts various levels of darkness and light. While this ability is continuously used, and it can mostly handle sudden lighting changes in the environment, the adaptation could still take several minutes. Moreover, during the adaptation, the color perception changes as well. This slow reactivity and perception change of the eyes could lead to mistakes for tasks performed in dazzling or temporally high-contrast environments such as when driving into the sun or during a welding process. We present AdaptiVisor, a vision augmentation system that assists the brightness adaptation of the eye. Our system selectively modulates the intensity of the light coming into the eyes via occlusion-capable Optical See-Through Head-Mounted Displays (OST-HMD). An integrated camera captures highlights and brightness in the environment via high-dynamic range capture, and our display system selectively dims or enhances part of feld of views so that the user would not perceive rapid brightness changes. We build a proof-of-concept system to evaluate the feasibility of the adaptation assistance by combining a transmissive LCD panel and an OST-HMD, and test it with a user-perspective, view-point camera. The evaluation shows that the system decreases the overexposed area in a scene to 1/15th, and enhances the color by reducing majorly underexposed area to half. We also include a preliminary user trial and it indicates that the system also works for real eyes for the HMD part and to some extent for the LCD.