A plano-convex optical sheet having a positive power including:
- a substantially planar inner surface;
- opposed lateral edges, and
- a thickness s that is decreasing proceeding from a transversal central
line passing through the geometric center of the optical sheet towards said opposed
lateral edges along a portion of predetermined width w of the optical sheet, so
as to define a convex outer surface having a curvature such that the optical sheet
is capable of providing once bent a cylindrically shaped optically correct visor.
