The first three books of the Book of Optics written by Alhazen in Cair
o in the eleventh century were translated into English by A I Sabra in
1989. Book I deals with optics, the structure of the eye, image forma
tion in the eye, and with the visual pathways. This book inspired all
other books on optics from the thirteenth to the seventeenth century a
nd formed the basis upon which Kepler solved the problem of image form
ation. However, Alhazen's work contained in Books II and III has been
almost totally ignored. These two books contain an account of hundreds
of observations and experiments carried out by Alhazen on a broad ran
ge of topics which are now studied under the heading of visual percept
ion. He clearly enunciated many of the fundamental principles which ar
e credited to scientists living in the last two hundred years, includi
ng a theory of unconscious inference; the law of equal innervation of
the eye muscles; the principles of binocular direction; constancy of s
ize, shape, and colour; induced visual motion; the vertical horopter;
the fusional range of binocular disparity; and many others.