The eye is a ball, and should be thought of that way. Beginning draughtsmen are often tempted to resort to the symbol for the eye - a flat, symmetrical almond-shape known to children - instead of rendering its spherical architecture. Of course, this makes dimensionality impossible.
The notable parts of the eye are the cornea and the sclera (SKLER-uh), which appears as the white of the eye. The whole ball of the eye is a little more than twice as wide as the the cornea. The cornea itself has some dimension, sitting like a dome upon the sphere of the rest of the eye.
The cornea contains the colored iris and the pupil, which is transparent but looks in on the dark chamber of the eye, and thus appears black. The pupil dilates and contracts depending on the amount of light falling on it.
The upper eyelid has two parts: the orbital portion and the lid plate. Between them is a fold into which the lid plate tucks itself when opened. Glands over the lateral part of the eye put the high point of this fold towards the medial side, whereas the lower border of the lid plate is a more regular arch. (But it should be remembered that the base of this arch rests deeper into the skull than its peak.) The closing of the eye is the work of the upper lid; the lower lid moves but little.
The lower lid plate follows the sphere of the eye as closely as the upper lid plate. Between the lower lid and the rest of flesh over the orbit is an important fold that distinguishes the two. In the lower medial corner of the orbit is the infrapalpebral (in-fruh-pal-PEEB-rul) furrow. The skin leading to this furrow is often of a different color than the surrounding skin, especially in subjects given to late nights.
The opening between the lids is called the lid slit. The corners are called the inner and outer canthus. In the outer canthus, the lower lid can be seen to tuck under the upper lid. In the inner canthus, the upper and lower lids are separated by a gulf called the lacrimal (LAC-rim-ul) lake, in which lies a pink gland called the caruncula (cuh-RUNK-you-luh). The lateral border of the caruncula is a crescesnt-shaped line against the eye. Tears originate from the inner canthus.
Because the sclera, cornea, and lids are layered sections of spheres, they receive light in a predictable manner. Presuming a light from above, the usual situation, the upper lid casts a shadow onto the eyeball. The highlight, which is often quite crisp because of the moisture on the eye, faces the light on the high side of the sphere. the lower part of the eyeball, turned away from the light, is in shadow. The lower lid, which follows the downward curve of the eyeball, is often in shadow except for its top plane.