A warming device (30) for warming the lens portion (2) of an optical instrument (1), such as a laparoscope, to a temperature above ambient to prevent lens fogging comprising: a double walled cylindrical tube (3) having an internal wall (3b), and an external wall (3a), an upper surface and an open distal portion (7) with a central cavity (4) therebetween a protrusion (9) extending from said upper surface, sized and shaped to receive the lens portion a circular cap (5) sized to attach to said distal portion of said double walled cylindrical tube and, a heating element (15) enclosed within said central cavity and thermally coupled to said insulation layer.
