Method for manufacturing an optical unit (1) comprising a plurality of glass-sheets (2) having an aspherical shape, arranged superimposed and spaced apart to form a stack (10), comprising the steps of: - arranging either a pre-bent or a flat glass-sheet (2) on a reference surface (5) having the geometry desired to be reproduced; - cold-deforming said glass-sheet (2) so as to adhere it onto the reference surface (5); - integrating said glass-sheet (2) with a preceding element (4, 2) of said stack (10) in a predetermined relative position; and - repeating the preceding steps till stack completion. The integration step comprises fastening said glass-sheet (2) in a position spaced from the preceding element (4, 12) of the stack (10) by means of bars (3) arranged spaced apart from one another.