A calibration method for a camera-based measuring device comprises positioning a calibration object simulating an anterior region of the eye on a holder arranged movably in a first direction relative to a camera of the measuring device within a view field of the camera. The first direction is toward and away from the camera substantially along a camera axis. A motorized drive unit, in drive connection with the holder, is firstly controlled to drive the holder, with the calibration object positioned thereon in the camera view field, relative to the camera along the first direction at least once past a position of maximum definition of an image of the calibration object taken by the camera. A ratio between an actual size and an imaging size of the calibration object is determined on the basis of a camera image of the calibration object taken at the position of maximum definition.
