Smiling with your eyes, known as the Duchenne smile, involves involuntary muscle movements. It is believed that one must be genuinely happy in order to smile with the eyes.
The Duchenne smile was named after French physician Guillaume Duchenne. In studying the physiology of facial expressions in the 19th century, Duchenne identified two distinct types of smiles: one that involves the eyes and mouth and one that solely involves the lips. Smiling with the eyes involves moving the orbicularis oculi muscle, raising the cheeks and producing wrinkles in the skin around the eyes. These movements are accompanied by voluntarily moving the zygomatic major, or the muscle that controls your lips. A genuine smile involves both muscles, while a fake smile only involves moving the zygomatic major.
In recent years, psychological studies have further complicated the distinction made by Duchenne and have revealed exceptions to his theory. Some actors have learned to move the orbicularis oculi muscle in order to produce what appears to be a genuine smile. In her paper, "The Deliberate Duchenne Smile: Individual Differences in Expressive Control," Sarah D. Gunnery examines how, in some instances, people within role-playing scenarios are able to produce the Duchenne smile. Her paper challenges the longstanding idea that the Duchenne smile can only be produced spontaneously.