1. 2. C. Scheiner Oculus, hoc est; Fundamentum Opticum. Daniel Agricola, Ocnoponli (Innsbruck] (1619 ).
2. 3. S. L. Polyak, The Retina . University of Chicago Press, IL, USA. pp. 136 -139 (1941 ).
3. G. B. Airy's model eye
4. 5. G. B. Airy, Letter to Dr Dionysius Lardner, April 25 . 1828 . (Original in Wellcome Historical Medical Library, reproduced in reference 4).