The Nature of Sight
I have remarked various opinions among philosophers concerning the causes of sight and the nature of vision. The Stoics affirm the causes of sight to be an emission of radii from the eyes against those things which are capable of being seen, with an expansion at the same time of the air. But Epicurus thinks that there proceed from all bodies certain images of the bodies themselves, and that these impress themselves upon the eyes, and that thence arises the sense of sight. Plato is of opinion that a species of fire and light issues from the eyes, and that this, being united and continued either with the light of the sun or the light of some other fire, by its own, added to the external force, enables us to see whatever it meets and illuminates.
But on these things it is not worth while to trifle further; and I recur to an opinion of the Neoptolemus of Ennius, whom I have before mentioned: he thinks that we should taste of philosophy, but not plunge in it over head and ears.