ANATOMY, EYE

Anatomic model of the human left eye (anterior view).
The eye is enclosed in the orbit, of which the roof is composed by the zygomatic bone and the maxilla.
The upper and lower eyelids (in gray) demarcate the palpebral aperture, by which the eyeball is visible. The inner and outer canthi of the eye are maintained by the medial and lateral palpebral ligaments, respectively.
Above the outer corner of the eye lie the two lobes of the lacrimal gland (in khaki; the superior orbital and inferior palpebral lobes), separated by the levator palpebrae superioris muscle. The lacrimal secretion flows through the ducts (in white) of the lacrimal gland, crosses diagonally the eyeball surface, and then passes in the inferior and superior lacrimal ducts (in beige) to join the lacrimal sac (in yellow), bulge of the nasolacrimal duct draining the tears.
In its anterior area, the eyeball includes the sclera (a white opaque tunic) opening on the cornea, a transparent membrane allowing to focus the image. Under the cornea, the colored iris includes several muscles controling the opening of the pupil (in black) and thus modulating the amount of light reaching the retina. In bright light, the contraction of the inner circular muscle constricts the pupil, while in dim light the contraction of the outer radial muscle dilates it.