The simplified, manual calibration of commercial Optical See-Through Head-Mounted Displays (OST-HMDs) is neither accurate nor convenient for medical applications. An interaction-free calibration method that can be easily implemented in commercial headsets is thus desired. State-of-the-art automatic calibrations simplify the eye-screen system as a pinhole camera and tedious offline calibrations are required. Furthermore, they have never been tested on original commercial products. We present a gaze-based automatic calibration method that can be easily implemented in commercial headsets without knowing hardware details. The location of the virtual target is revised in world coordinate according to the real-time tracked eye gaze. The algorithm has been tested with the Microsoft HoloLens. Current quantitative and qualitative user studies show that the automatically calibrated display is statistically comparable with the manually calibrated display under both monocular and binocular rendering mode. Since it is cumbersome to ask users to perform manual calibrations every time the HMD is re-positioned, our method provides a comparably accurate but more convenient and practical solution to the HMD calibration.