A computer-implemented method for determining a position of a center of rotation of an eye of a person in an arbitrary world coordinate system using a mobile device including a camera (11, 12),at least one sensor, and at least one of a display or a loudspeaker, the method comprising: capturing a first image while the person looks at a first direction, and capturing a second image while the person looks at a second direction, and determining the position of the center of rotation based on the first image and the second image, wherein capturing the first image comprises capturing the first image with the camera (11, 12) of the mobile device while the mobile device is in a first position relative to a head of the person in the arbitrary world coordinate system, wherein the first direction is a direction to the camera (11,12) of the mobile device or a target displayed on the display of the mobile device in the first position, characterized in that the method further comprises: displaying instructions on the display of the mobile device or outputting instructions from the loudspeaker of the mobile device to move, by the person or another person, the mobile device from the first position to a second position relative to the head of the person, wherein the first position and the second position in the arbitrary world coordinate system is determined using at least one sensor of the mobile device, wherein capturing the second image comprises capturing the second image with the camera (11, 12) of the mobile device while the mobile device is in the second position in the arbitrary world coordinate system different from the first position, wherein the second direction is a direction to the camera (11,12) of the mobile device or a target displayed on the display of the mobile device in the second position, wherein the first and second images are captured while the person keeps the head in the same position with the eye looking at the first and second directions, respectively, and wherein determining the position of the center of rotation is further based on the first position of the mobile device and the second position of the mobile device. capturing a first image while the person looks at a first direction, and capturing a second image while the person looks at a second direction, and determining the position of the center of rotation based on the first image and the second image, wherein capturing the first image comprises capturing the first image with the camera (11, 12) of the mobile device while the mobile device is in a first position relative to a head of the person in the arbitrary world coordinate system, wherein the first direction is a direction to the camera (11,12) of the mobile device or a target displayed on the display of the mobile device in the first position, characterized in that the method further comprises: displaying instructions on the display of the mobile device or outputting instructions from the loudspeaker of the mobile device to move, by the person or another person, the mobile device from the first position to a second position relative to the head of the person, wherein the first position and the second position in the arbitrary world coordinate system is determined using at least one sensor of the mobile device, wherein capturing the second image comprises capturing the second image with the camera (11, 12) of the mobile device while the mobile device is in the second position in the arbitrary world coordinate system different from the first position, wherein the second direction is a direction to the camera (11,12) of the mobile device or a target displayed on the display of the mobile device in the second position, wherein the first and second images are captured while the person keeps the head in the same position with the eye looking at the first and second directions, respectively, and wherein determining the position of the center of rotation is further based on the first position of the mobile device and the second position of the mobile device. displaying instructions on the display of the mobile device or outputting instructions from the loudspeaker of the mobile device to move, by the person or another person, the mobile device from the first position to a second position relative to the head of the person, wherein the first position and the second position in the arbitrary world coordinate system is determined using at least one sensor of the mobile device, wherein capturing the second image comprises capturing the second image with the camera (11, 12) of the mobile device while the mobile device is in the second position in the arbitrary world coordinate system different from the first position, wherein the second direction is a direction to the camera (11,12) of the mobile device or a target displayed on the display of the mobile device in the second position, wherein the first and second images are captured while the person keeps the head in the same position with the eye looking at the first and second directions, respectively, and wherein determining the position of the center of rotation is further based on the first position of the mobile device and the second position of the mobile device.