e do not intend to go into very great detail in this section. Those of you “pearl divers” who want more will have to dig deeper.

Figure 1. The orbit and associated structures. (click each to enlarge)

The orbit is the bony ‘socket’ which encloses and protects the eye (globe) and other structures associated with the eye.

The extraocular muscles are responsible for all movements of the eye.

Figure 2a. Frontal view of the eye and attached muscles (left). Figure 2b. Isometric side view of the eye and attached muscles (right).

Behind the upper eyelid lies the lacrimal gland which provides the tears to keep the eye moist and our contact lenses from sticking to our eyes. The lids act like windshield wipers but also serve to keep the eye from completely drying out by spreading the tears around. The tears themselves are a complex mixture of water, electrolytes, lipid, antibodies, and waxy material — some components of which are supplied by the goblet cells located at the periphery of the cornea — the limbus.

The sclera is the leathery shell of the eye. It is covered in the front by the conjunctiva — the so-called “white of the eye”. It is the blood vessels within the conjunctiva which produces the tell-tale “blood shot” appearance on certain occasions.

Figure 3. External segment. Note that the pupil is not centered within the iris.