Ibn al-Haytham (965-1039) is generally thought to be the only Islamic contributor to optics with his Kitab al-manazir (Book on Optics). In the more erudite works on the subject, such as by Lindberg, one finds other Muslim scientists involved in the subject.[1] Rashed, too,  has made extensive studies with respect to some authors such as al-Farisi.[2] Djebbar makes a brief list of other authors and their works:

-Al-Kindi (801-873): Risala fi ikhtilaf al-manazir (Treatise on Divergences in Optics).

Risala fi islah kitab Uqlidis (Book on the Corrections of the Optics of Euclid.

-Ibn Isa (10^th c): Kitab fi l-hala wa qaws quzah (Book on the Halo and the Rainbow).

-Ibn Mansur (10^th c): Kitab al-Manazir (Book on Optics)

-Al-Farisi (13^th c): Tanqih al-manazir (Revision of the Book of Optics).

-Ibn Ma’ruf (16^th ): Kitab nur hadaqat al-absar (Book on the Light of Accuity…)[3]

The following outline is unable to go into these works and will focus instead on pre-Islamic optics and on Ibn al-Haytham.

Pre-Islamic (Greek) Theories of Vision

Optics remained for about thirteen centuries the battlefield of the Greeks and their followers, the symbol of cogitation and speculation triumphant over experimentation. The Greeks were roughly divided into two diametrically opposed camps around the issue of vision; those who stood by the ‘intromission' theory, something entering the eyes representative of the object, and those who stood by ‘emission,' vision occurring when rays emanate from the eyes and are intercepted by visual objects.[4]

Within each half of the argument, there were more divisions. Omar  explains that among intromission theorists, opinion varied considerably, for example around the manner in which the image is transmitted to the eye, the nature of the medium, and so on.[5] The difficulty in coming to a cohesive, precise conclusion on optics resided with the multiplicity of the arguments, and the fact that proponents of different arguments were inconsistent on many accounts.[6]

Without getting bogged down in the complexities of the Greek arguments, here is a brief outline of the issue of vision as it stood before the Muslims.[7]

Basically, as Omar  explains, there were two diametrically opposed Greek theories of vision. The first, the intromission theory (Aristotle, Galen and followers), explained vision in terms of the entry into the eye of ‘something' representative of the object. Opposed to this was the emission theory (Euclid and Ptolemy and followers,) which held that vision occurs when rays emanate from the eye and are intercepted by visual objects.[8]

Almost without exception, the Greek intromission theorists were physicists, and so adopted a physical approach to the problem of vision. Before Aristotle, Greek Atomists sought to apply philosophical views, explaining vision in terms of ‘a coherent form, a thin film of atoms encompassing the object, which leaves the object and enters the eye.’[9] Aristotle's theory itself is largely based on general observations, interpreted according to his own philosophical system. The relation between the eye and the object is not made clearer by Aristotle's denial of emission from the object. On the halo and the rainbow, he even adopts a theory, which is contrary to his own.[10] The fact is that, while the intromission theory, and its various versions, seems physically more sound than the emission theory, it lacks the ability to explain the manifold phenomena presented by vision.[11]

The emission theory (Euclid and his followers,) maintains that a ray issues from the eye and proceeds to the object of vision where its termination constitutes the act of vision. The idea of radiation from the eye relies (due to its author (Euclid) on geometrical explanations for vision. It fails to take account of physical, physiological and psychological elements that affect vision. Ptolemy sought to harmonise the geometric with physical approach. He even carried out some experiments in support of his views. The problem, as raised by both Omar  and Hill, was that his experimentation was to support his already preconceived theory, even manipulating experiments for that purpose,[12]  which is the exact opposite of what experimentation is supposed to achieve.

Both intromission and emission theories, thus, suffer from exactly what Greek science suffers from: its reliance on cogitation and the lack of experimental foundation.

In explaining the passage from Greek to Islamic optics, Lindberg, very ingeniously, subdivides Greek optical theories into five main strands:

1) Aristotle's description of light as the actualisation of the potential transparency of a medium by imposition of a form on the medium and his intromission theory of vision.

2) Neoplatonic views on the emanation of power.

3) The opinion of Galen and others on the anatomy of the eye and the physiology of sight.

4) The intromission theory of the atomists.

5) The geometrical tradition originated by Euclid and Ptolemy.

It should be noted, Lindberg adds, that all of these strands, except perhaps the second, are principally concerned with one very fundamental question: How do we see? consequently, they involve questions of a physiological and psychological sort as well as of physics and mathematics.[13]