THE EYE IS THE CENTER OF EVERYTHING THAT ONE SEES.

As all visible things take their origin from the eye, so it is the center of what one sees. And as the eye is different in its form for each person, so it is that each thing that we see seems large to some and small to others. It seems that the reason comes from the form of the eye, for the point from which we see is not on the surface of the eye but is inside it. And the visible thing comes to represent itself on the surface of the eye, which is like a glass. And being there, the point of sight (which is a drop of water otherwise called the optic nerve the nerve carrying visual information to the brain) looks at the thing seen on the surface of the eye. And according to how close said point of sight is to the surface of the eye, so we have short or long sight, as for example: let the point of sight, or drop of water, or optic nerve (whatever it may be, for it is but a point from which we see) be marked A. And let the surface of the eye, which is like a glass, be marked B C. And let the visible thing be D E. Let the visual rays be drawn from the point A to the visible thing, passing through the surface of the eye B C; then the visible thing will be seen of the size B C on the surface of the eye G H. And the visible thing I L, and draw the visual rays as above: it is certain that the visible thing is represented to the eye A as larger than to the one F. And from this it happens that there are several people, and notably in Portugal, who have the point of sight so deep in the head that everything they see seems so large because the visual rays dilate so far from one another that they are certain to wear shortening spectacles meaning concave lenses for myopia to help gather the visual rays to, by this means, distinguish the visible thing better. Now, these same people have a great advantage in what they see from near, in that they see delicate things more perfectly and also are very fit for doing delicate work, for by comparison the size of a grain of vetch will seem to them as large as a pea does to others.

Two geometrical diagrams illustrate the optics of the eye. The left diagram shows a point A (the point of sight) behind a curved surface BC (the surface of the eye), with diverging visual rays extending to a larger object DE. The right diagram shows a point F further back from a surface GH, with rays extending to an object IL, demonstrating how the depth of the point of sight affects the perceived size of the object.