Spiral dioptre with meridians of different optical power

An optical device for providing a lengthened focal region and having an optical axis, the optical device comprising at least one surface with at least two meridians, at least one portion of said surface forms, seen face-on, at least one spiral segment the central point of which is on the optical axis, each spiral segment defining meridians of different optical powers, in order that the focus obtained extends over a tubular region having an elongation parallel to the optical axis and is retained the same throughout the elongation, the one or more spiral segments being bounded by border lines, with each border line being a spiral border line, see face-on, that extends from the center point, having a surface contour that follows a surface pattern of a toric surface that has been spiralized by twisting about the center point, and having a first meridian curved with a first non-zero curvature and a second meridian curved with a second curvature strictly greater than the first curvature, the second meridian being perpendicular to the first meridian.