A device for containing emboli within a left atrial appendage of a patient includes a frame that is expandable from a reduced cross section to an enlarged cross section and a slider assembly. The area of the substrate is greater than the area of the optical sheet. The lubricant oil supplying apparatus further includes a suppression structure of suppressing flow of the lubricant oil in the first passage from a connection part to the second passage toward the outflow port. The shape and dimensions of each of the at least one optical structure are determined in part by at least one randomly generated component of modulation wherein the modulation of each of the at least one optical structure is limited by a neighboring optical structure comprised by the surface.