A variable focal length lens includes a central transparent elastic portion having a first wall and a second wall intersecting an optical axis and a peripheral portion surrounding the body. The LED element is detachably supported by the plate spring-like conductive terminals through the feeding terminals and receives a power supply from both sides of the feeding terminals. 09 nm, which enables to manufacture an n-MOS transistor of a high mobility. Systems and methods of nerve stimulation and selective nerve stimulation are also provided to artificially stimulate deglutition.