Page 929 - Atlas of Histology with Functional Correlations

protect the eyes from foreign objects and excessive light. Situated above each

eye is a secretory lacrimal gland that continually produces lacrimal
secretions or tears. Blinking spreads the lacrimal secretion across the outer
surface of the eyeball and the inner surface of the eyelid. The lacrimal
secretion contains numerous proteins (tear albumins, lactoferrin), mucus,
salts, and the antibacterial enzyme lysozyme. Lacrimal secretions clean,

protect, moisten, and lubricate the surface of the eye (conjunctiva and
cornea).

The tarsal glands produce an oily secretion that forms a surface layer on
the tear film that prevents the evaporation of the tear layer and lubricates the

ocular surface. The sweat glands (of Moll) produce and empty their
secretions into the follicles of the eyelashes.

AQUEOUS HUMOR

Aqueous humor is produced by the ciliary epithelium of the ciliary process
in the eye. This watery fluid flows from the posterior chambers through the

pupil into the anterior chamber of the eye between the cornea and lens.
Aqueous humor maintains the intraocular pressure, bathes the nonvascular
cornea and lens, and also supplies them with nutrients and oxygen. The fluid
is continuously reabsorbed in the angle between the cornea and iris into the

canal of Schlemm and the veins of sclera.

VITREOUS BODY

The vitreous chamber of the eye is located behind the lens and contains a
gelatinous substance called the vitreous body, a transparent colorless gel that
consists mainly of water. In addition, the vitreous body contains small

amounts of hyaluronic acid, very thin collagen fibers, glycosaminoglycans,
and some proteins. The vitreous body transmits incoming light, is
nonrefractive, maintains the intraocular pressure and shape of the eyeball,
and supports the retina against shock and vibration.

RETINA

The photosensitive retina contains photoreceptive rods and cones, bipolar

cells, and ganglion cells distributed in different layers. The rods and cones
are receptor neurons essential for vision. They synapse with the bipolar cells,
which then connect the receptor neurons with the ganglion cells. The afferent

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