An optical scanning device is for scanning an information layer (2) with a radiation beam (4). It includes: a radiation source (6) for providing said radiation beam, a lens system (7) for transforming said radiation beam to a scanning spot (17) on said information layer, and a wavefront modifier arranged between said radiation source and said scanning spot. The modifier including two elements (301, 302) having each an aspheric surface (301b, 302a) and being mutually linearly movable for introducing a wavefront modification in said second radiation beam. According to the invention, the aspheric surfaces are shaped so that: a first mutual linear displacement of the elements (301, 302) introduces a first wavefront modification (Wa) along a first axis (XO) in said second radiation beam, and a second mutual linear displacement of the elements introduces a second wavefront modification (Wb) along said second axis (YO) in said second radiation beam.