The eye

The eye can be divided into a front and rear section. The front section of the eye consists of the cornea, the anterior chamber, the iris, the lens and the posterior chamber. The inside of the eye behind the iris and the lens is filled by the vitreous. This is similar in form and consistency to uncooked egg white. The eye is limited at the back by three layers of tissue: the retina, the choroid and the sclera. The retina contains the macula or yellow spot, the area of maximum visual acuity. Alongside the macula the optic nerve enters the eye where it forms the optic disc or papilla.

In order for the eye to retain its spherical shape, a certain level of internal pressure must be maintained. This task is fulfilled by the aqueous humour which fills the anterior and posterior chamber of eye, i.e. the space between the cornea, the iris and the lens. The aqueous humour is produced by the tissue of the ciliary body directly behind the iris. From the ciliary body the aqueous humour flows through the pupil into the anterior chamber where it is led off out of the eye via the iridocorneal angle.
The eyes lie well protected in the orbital cavities, embedded in fatty and connective tissue. Six external eye muscles ensure rapid and precise movement of the eyeball.
As our eyes are constantly exposed to environmental influences such as sunshine, cold, dust or pathogens, they need special protection. This includes eyebrows, eyelids, conjunctiva and tear glands.
The eyebrows form a kind of protective screen against exposure to sunlight from above. The lower and upper eyelids close reflexively in a fraction of a second if there is any threat to the eye. The lids also protect the eyes while we are asleep.
The blinking reflex of the lids ensures that the cornea and the conjunctiva are kept moist at all times. The tear fluid is salty, it prevents the eyes from becoming too dry, protects against infection and supplies nutrients to the cornea.

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