CHAPTER 20
Eye
395
Eyelash
Eyelash
follicles
follicles
Gland of Moll
Gland of Moll
Eyelash
follicles
Eyelashes
Gland
of Zeis
Gland of Moll
Tarsal
plate
Palpebral
conjuctiva
Meibomian
(tarsal)
gland
Gland
of Zeis
A
Figure 20-4A.
Upper eyelid (lower part), glands of the
eyelid.
H&E,
3
68
Eyelids
(
palpebrae
) consist of upper and lower eyelids. The
structural components of the
upper eyelid
are similar to
those of the
lower eyelid
, although the upper eyelid is more
mobile.
Eyelashes
and their follicles are visible at the margin
of the eyelid. The
tarsal glands
, also called
meibomian
glands
, are large sebaceous glands embedded in the tarsal
plate. The glands associated with eyelashes are (1)
glands
of Moll
and (2)
glands of Zeis
. The glands of Moll are
modiF
ed sweat glands near the base of the eyelash. They
have unbranched tubules, which begin in a simple spiral
rather than coiling in a glomerular shape, as do ordinary
sweat glands (see ±ig. 20-3B). The glands of Zeis are small,
modiF
ed sebaceous glands that are sometimes called
ciliary
glands
. They are close to the eyelash follicles and empty
their secretions into the follicles.
Meibomian
(tarsal)
gland
Hair
follicles
Skin
Palpebral
conjuctiva
Orbicularis
oculi muscle
Orbicularis
oculi muscle
Duct of
tarsal
plate
B
Figure 20-4B.
Upper eyelid (middle part).
H&E,
3
68
The
outer layer of the eyelid
is covered by
thin skin
(see ±ig.
3-13 and Chapter 13 “Integumentary system”), a keratinized
stratiF
ed squamous epithelium, over a loose elastic con-
nective tissue layer. The skin contains
hair follicles,
which
are much smaller than
eyelash follicles
(found only in the
lid margin; see ±ig. 20-3A).
Orbicularis oculi muscle ± bers
are located beneath the skin. The inner surface of the lid is
a layer of
palpebral conjunctiva
, covered by stratiF
ed low
columnar epithelium, which is in contact with the eyeball.
The
tarsal
(
meibomian
)
glands,
embedded in the tarsal plate,
lie between the orbicularis muscles and palpebral conjunc-
tiva. Each gland has a single duct that opens at the lid mar-
gin. Their lipid secretion creates a surface on the tear F
lm
that prevents lacrimal fl
uids (
tears
) from evaporating from
the surface of the eyeball. This secretion also lubricates the
cornea and edges of the eyelids.
Orbicularis
Orbicularis
oculi muscle
oculi muscle
(skeletal muscle)
(skeletal muscle)
Meibomian
(tarsal)
gland
Superior
tarsal
muscle
Orbicularis
oculi muscle
Orbicularis
oculi muscle
(skeletal muscle)
Tendon of the
levator
palpebrae
muscle
C
Figure 20-4C.
Upper eyelid (upper part), muscular
control
of upper eyelid movement.
H&E,
3
68; inset
3
272
Three types of
muscles
control
upper eyelid movement
.
(1) The
orbicularis oculi muscle
is a sheet of striated muscle
that is oriented in a circle around the eye. It is innervated by
the facial nerve (CN VII) and is responsible for closing the
eyelids. (2) The
levator palpebrae superioris muscle
is a band
of striated muscle that originates in the orbit, passes forward,
and inserts into the upper eyelid. This muscle is innervated
by the oculomotor nerve (CN III) and functions to open the
eyelid and hold it up. The levator palpebrae muscle is not vis-
ible here, but its tendon is clearly seen. (3) The
superior tarsal
muscle
, also called the
Müller muscle
, is a smooth muscle
that inserts on the superior tarsal plate. It is innervated by
sympathetic nerve F
bers from the superior cervical ganglion
and works with the levator palpebrae superior muscle to
raise the upper eyelid. Damage to the levator palpebrae supe-
rior muscle, the superior tarsal muscle, or their innervation
can cause
ptosis
(drooping of the eyelid).
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