1. A method of obtaining geometrical information about an object, comprising: transversely scanning the object with an OCT instrument including a low coherence interferometer to obtain an en-face OCT image; introducing differential delays with known values into a path of light, wherein said light passes through said interferometer to produce an output beam comprising multiple parallel beam portions having different path lengths associated therewith, and thereby generating in said en-face OCT image a set of two dimensional image contours at different depths, each said two dimensional image contour corresponding to a said respective beam portion, and said two dimensional image contours having a known depth relationship determined by said differential delays; and computing the geometrical information about the object from at least two of said of said sets of two-dimensional contours in the said en-face OCT image.