Figure 1.

Illustration depicting on-axis and off-axis scans. The on-axis scan (top row) is acquired by selecting a pupil location so that the B-scans in the horizontal (marked in green) and the vertical (marked in red) directions appear flat. The off-axis scan is acquired by selecting a pupil location eccentric to the previous location. Here, a location to the right of the on-axis scan pupil position induces a tilt in the B-scan (marked in green) corresponding to the horizontal direction. Similarly, a pupil location above or below the on-axis scan pupil location would induce a tilt in the B-scan corresponding to the vertical axis.