How was Allvar Gullstrand awarded the Noble Prize in Physiology or Medicine?

Name: Allvar Gullstrand .
Country: Sweden.
Date of Birth: 5 June 1862.
Died: 28 July 1930.
Education: University of Uppsala.
Subjects Of Study: Eye light refraction.
Known as: Mathematical model of the human eye, research on astigmatism.
Noble Prize Year: Nobel Prize for Peace in 1911, for his research on the eye as a light-refracting apparatus.