The Anatomy of the Eye
With every blink of the eyes the lids wash the cornea and conjunctiva with tears.
They are formed by the lacrimal gland and the
accessory lacrimal glands.
A healthy tear is composed of 3 layers: the lipoid, aqueous, and mucoid.
If there is any defect in these layers
the integrity of the cornea may become compromised. Tears are secreted in response to reflex or emotional stimuli.
The conjunctiva, a mucous membrane, provides a barrier to the external environment and nourishes the eye.
The goblet cells of the
conjunctiva secrete lubricating mucous.
The sclera, AKA the white of the eye, is a dense, fibrous structure that comprises the posterior 5/6’s of the eye.
It helps to maintain the
shape of the eyeball and protects the intraocular contents from trauma.
It may have a slightly blue tinge in young children, a dull white
color in adults, and a slight yellow color in the elderly.
Externally it is overlaid with conjunctiva, which is a thin, transparent, mucous
membrane that contains fine blood vessels.
The conjunctiva meets the cornea at the limbus on the outermost edge of the iris.
The cornea, a transparent, avascular dome-like structure, forms the most anterior portion of the eyeball and is the main refracting surface
of the eye.
Behind the cornea lies the anterior chamber, filled with a continually replenished supply of clear aqueous humor, which nourishes the
cornea. The aqueous humor is produced by the ciliary body, and its production is related to the IOP (10-21 mm Hg)
The iris, or colored part of the eye, is a highly vascularized, pigmented collection of fibers surrounding the pupil.
The pupil is a space that dilates and constricts in response to light.
Normal pupils are round and constrict symmetrically when a bright
light shines on them.
Dilation and constriction are controlled by the sphincter and dilator pupilae muscles.
The dilator muscles are
controlled by the SNS and the sphincter muscles are controlled by the PNS.
Directly behind the pupil and iris lies the lens, a colorless and almost completely transparent.
It is avascular and has no nerve or pain
The lens enables focusing for near vision and refocusing for distance vision.
The ability to focus and refocus is called
The aqueous humor is anterior to the lens and the vitreous humor is posterior to the lens.
All cells formed throughout life are retained by the lens, which makes the cell structure of the lens susceptible to the degenerative effects
The posterior chamber is a small space between the vitreous and iris.
Aqueous fluid is manufactured here by the ciliary body.
from the posterior chamber into the anterior chamber, from which it drains through the trabecular meshwork and the canal of Schlemm.