Bruce Eastwood

Alhazen, Leonardo, and late-medieval speculation on the inversion of images in the eye

Summary No one before Platter and Kepler proposed retinal reception of an inverted visual image. The dominant tradition in visual theory, especially that of Alhazen and his Western followers, subordinated the intra-ocular geometry of visual rays to the requirement for an upright image and to preconceptions about the precise nature of the visual spirit and its part in vision. Henry of Langenstein and an anonymous glossator in the late Middle Ages proposed alternatives to Alhazen, including the suggestion of double inversion of the image. Leonardo da Vinci was aware of both Alhazens theory and Henrys contradiction, but perhaps not of the anonymous hypothesis of double inversion. Leonardos visual ‘theory’ has more the character of a critique than of a theoretical alternative, and he did not transcend the medieval concept of visual spirit.

Theories of Vision from Al-Kindi to Kepler

Preface 1: The Background: Ancient Theories of Vision 2: Al Kindis Critique of Euclids Theory of Vision 3: Galenists and Aristotelians in Islam 4: Alhazen and the New Intromission Theory of Vision 5: The Origins of Optics in the West 6: The Optical Synthesis of the Thirteenth Century 7: Visual Theory in the Later Middle Ages 8: Artists and Anatomists of the Renaissance 9: Johannes Kepler and the Theory of the Retinal Image Appendix: The Translation of Optical Works from Greek and Arabic into Latin Notes Selected Bibliography Index