dilator muscles, which work in opposition to one another and are inner-
vated by parasympathetic and sympathetic fibers, respectively. The center
of the iris is a “hole,” the pupil.
The ciliary body contains the ciliary muscles (EandK).The ciliary mus-
cles stretch the choroid and relax the lens, which is essential for the process of
lens accommodation. The ciliary processes (F)extend from the ciliary body
and produce aqueous humor. They are also the origin of the zonule fibers (G),
which are similar in structure to elastic fibers and are important for anchorage
of the lens. The zonule fibers are involved in accommodation. When the cil-
iary muscles contract, causing forward displacement of the ciliary body, the
tension on the zonule fibers is reduced, which leads to an increase in lens
thickness and maintenance of focus. The aqueous humor produced by the cil-
iary processes (F)is transported into the posterior chamber (N)and flows
into the anterior chamber (O)through the pupil. Outflow from the anterior
chamber occurs through the trabecular meshwork at the iridocorneal angle
and flows through the canal of Schlemm.
The cornea (A)forms the transparent, avascular anterior portion of the
eye. The outer anterior surface of the cornea is covered by an epithelium.
Beneath the epithelium is Bowman’s membrane, the corneal stroma,
Descemet’s membrane, and the endothelium (at the posterior surface of the
cornea), which lines the anterior boundary of the anterior chamber.
The lens (J)is formed embryologically from a thickening of the surface
ectoderm called the lens placode, which eventually forms a lens vesicle.
Lens fiber production continues throughout life with no turnover. The lens
is surrounded by a capsule and an underlying epithelium (HandL).The
three compartments of the eye include the posterior and anterior cham-
bers, which are filled with aqueous humor, and the vitreous body (M),
which is filled with a gel consisting of hydrated hyaluronic acid and other
glycosaminoglycans.
The conjunctiva is the mucosa, or lining, of the eyelid and is labeled I
in the figure.
267.The answer is d.(Junqueira, pp 462–466.)The inner nuclear layer is
responsible for the integration of data from adjacent photoreceptors. The
retina consists of 10 layers:
- The retinal pigment epithelium (RPE) is derived from the outer wall of
the optic cup. The RPE functions in the phagocytosis of rod disks.
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