Kitap 7
7
I have already made mention elsewhere of cataract, because when of recent origin it is also often dispersed by medicaments: when it is more chronic it requires treatment by surgery, and this is one of the most delicate operations. Before I speak of this, the nature of the eyeball itself has to be briefly explained. A knowledge of this is often useful, but especially here. The eyeball, then, has two external tunics, of which the outer is called by the Greeks ceratoides. In that part of the eye which is white it is fairly thick; over the region of the pupil it is thin. To this tunic the under one is joined; in the middle where the pupil is, it is pierced by a small hole: around this it is thin, further out it too is thicker and is called by the Greeks chorioides. These two tunics whilst enclosing the contents of the eyeball, coalesce again behind it, and after becoming thinned out and fused into one, go through the space between the bones, and adhere to the membrane of the brain. Under these two tunics, at the spot where the pupil is, there is an empty space; then underneath again is the thinnest tunic, which Herophilus named arachnoides. At its middle the arachnoides is cupped, and contained in that hollow is what, from its resemblance to glass, the Greeks call hyaloides; it is humour, neither fluid nor thick, but as it were curdled, and upon its colour is dependent the colour of the pupil, whether black or steel-blue, since the outer tunic is quite white: but this humour is enclosed by that thin membrane which comes over it from the interior. In front of these is a drop of humour like white of egg, from which comes the faculty of seeing; it is named by the Greeks crystalloides.
