A method of operating a microsurgical instrument, such as a vitrectomy probe, is disclosed. The platform includes a hull, legs movable relative to the hull, at least one brace frame movably connected to at least two of the legs. A slit plate limits the light flux on the exit side of the condenser lens. The protrusion portion is provided at an inner wall part which confronts the roller surface of the developing roller and where the residual toner begins to drop from the developing roller.