1. Huxley A. The art of seeing. New York: Harper and Brothers; 1942.
2. Bates WH. Perfect sight without glasses. New York: Central Fixation Publishing Co.; 1920.
3. Riva MA, Arpa C, Gioco M. Dante and asthenopia: a modern visual problem described during the Middle Ages. Eye. 2014;28:498.
4. Chesterton GK. The Innocence of Father Brown. London, New York, Toronto and Melbourne: Cassell & Co Ltd; 1911.
5. Groddeck G. Nasamecu. Der gesunde und kranke Mensch gemeinverständlich dargestellt. Leipzig: Hirzel; 1913.