Anatomy of the eye

We say: the visual force and matter of the optic pneuma penetrates the eye along the path of both hollow nerves, which you have already become familiar with in anatomy. As the nerves and membranes that are connected to them descend to the eye socket, their ends expand, fill and spread so much that they can cover the moisture that is in the eyeball. Of these, the middle one is icy. This transparent moisture is similar to hailstones and pieces of ice, has a round shape, but its roundness decreases in front due to flatness, so that the reflection in it is fuller in size, so that small visible objects find a large area in which they are reflected. Therefore, the back of it tapers slightly so that the bodies that embrace it can better cover it. These bodies are narrow at first, and then spread out in width to better embrace the icy moisture.

This moisture is placed in the middle of the eye, because in terms of preservation this is the best of places. Behind it there is another moisture, which descends to it from the brain to nourish it, since between the first moisture and pure blood the second moisture forms an intermediate stage. The second moisture is like molten glass. The color of this molten glass is transparent, but tends towards a slightly reddish color. This moisture is transparent, because it must nourish the transparent. It is reddish because it comes from the blood substance. It is not completely like that which nourishes, and is located behind the icy moisture, because it represents what is sent to it by the brain through the retina; therefore, it is necessary that the vitreous moisture be located in the same place as the icy one. This moisture covers the back half of the icy moisture to the largest circle.

Before the icy moisture there is a third moisture, similar to egg white - it is called albuminous. It is like a secretion that comes out of the icy moisture, but the secretion of the transparent is transparent. It is located in front of the icy moisture due to one primary cause and due to one additional cause. The primary reason is that the dedicated part is located on the opposite side to the supply part. An additional reason is that the penetration of light into the icy moisture occurs in steps and that a kind of cover is created for it. Further, the terminal extensions of the optic nerve cover the vitreous and icy humor to the border between the glacial humor and the albuginic. The limit to which the glassy moisture reaches is located on the crown in the same way as the net covers the prey. Therefore, this terminal extension of the optic nerve is called the retina. A web grows from its anterior end, from which a thin hymen is born. Along with this hymen, threads from the vascular part penetrate, which we will talk about later. This hymen forms a barrier between the icy moisture and the albumen, so that there is something separating between the thin and the thick, and so that the hymen itself from the front receives nutrition that comes from the retina and choroid. And it is thin, like a spider’s web, only because if it were dense, being located directly in front of the icy moisture, then the latter, due to a change in its state, might begin to obstruct the light on its path through the icy moisture to the albuminous one.

As for the end of the thin membrane, it is filled and woven into the blood vessels like a newborn’s shirt: truly, it conducts nutrients. However, there is no need for all its parts to serve nutritional purposes; this is done only by its back part, which is called the choroid.

As for the part that protrudes forward beyond this boundary, it becomes a thicker skin of a heavenly color, between white and black, in order to collect visual power and moderate the light with its action, just as we close our eyes when we are tired. protection from darkness or from a combination of darkness and light, and also in order to form a barrier between moisture and the cornea, which has great hardness, in order to be a balancing mediator between them, and also in order to nourish the cornea with what it itself receives from the choroid. In front, it does not completely cover the eyes, so as not to impede the penetration of images of visible objects, but leaves a gap or hole in its front part, as happens in a grape if the stem is torn off from it. Through this hole the image penetrates, but if it closes, vision stops.

On the inner surface of this grape skin there is a fleecy body in the place where it meets the icy moisture, so as to more closely resemble a loose and soft body there and thus avoid harm from touching it. The grapevine is harder in its anterior part, where it meets the hard cornea, and also where it has an opening, so that its circumference is stronger. This hole is full of moisture for the sake of the benefit already mentioned, and also full of pneuma: as indicated by the appearance of wrinkles on the eye in front of the optic hole when death approaches.

As for the second shell, it is very thick in order to hold well. Its back part is called the hard and thick shell; the front part surrounds the entire pupil and is transparent so as not to interfere with vision. Therefore, this part has the color of a piece of horn, refined by filing and scraping, and is therefore called the cornea. It is thickest in the front part and in fact is made up of four thin layers, which can be compared to peels placed one on top of the other, so that no harm occurs if one of them is torn off, especially in the part that is located opposite visual opening, since this place most of all needs cover and protection.

As for the third shell, it merges with the motor muscles of the eye and is all overgrown with white fatty meat, so that the eye and eyelid are soft and prevent them from drying out. This entire membrane is collectively called the connective membrane. As for the muscles of the eyeball, we have already mentioned them in anatomy.

As for the eyelashes, they are created in order to reflect what falls into the eye, and what falls onto it from the head, and to moderate the light with their blackness. Their roots sit in a kind of shell, similar to cartilage, so that they hold tightly and do not fall due to the weakness of the landing site and so that the muscle that opens the eye has a support point, like on a bone, so that it moves well eyelid. The parts of the eyelid are as follows: the skin, then the connective layer, then its fat, then its muscles, then the last layer. This is the upper eyelid. As for the lower one, it has no muscle. The place that is dangerous to cut is the one located above the inner corner of the eye, at the beginning of the muscle.