The orbicularis oculi is a muscle in the face that closes the eyelids. It arises
from the nasal part of the frontal bone, from the frontal process of the maxilla
in front of the lacrimal groove, and from the anterior surface and borders of
a short fibrous band, the medial palpebral ligament.
From this origin, the fibers are directed lateralward, forming a broad
and thin layer, which occupies the eyelids or palpebræ, surrounds the
circumference of the orbit, and spreads over the temple, and downward on the
cheek. The palpebral portion of the muscle is
thin and pale; it arises from the bifurcation of the medial palpebral
ligament, forms a series of concentric curves, and is inserted into the lateral
palpebral raphe at the outer canthus of eye.
The orbital portion is thicker and of a reddish color; its fibers form a
complete ellipse without interruption at the lateral palpebral commissure; the
upper fibers of this portion blend with the Frontalis and Corrugator.
The lacrimal part is a small, thin muscle, about 6 mm in breadth and 12 mm
in length, situated behind the medial palpebral ligament and lacrimal sac. It
arises from the posterior crest and adjacent part of the orbital surface of
the lacrimal bone, and passing behind the lacrimal sac, divides into two
slips, upper and lower, which are inserted into the superior and inferior
tarsi medial to the puncta lacrimalia; occasionally it is very indistinct.
Actions The muscle acts to close the eye, and is
the only muscle capable of doing so. Loss of function for any reason results
in an inability to close the eye, necessitating eye drops at the minimum
to removal of the eye in extreme cases. The palpebral portion acts
involuntarily, closing the lids gently, as in sleep or in blinking; the orbital
portion is subject to conscious control. When the entire muscle is brought into
action, the skin of the forehead, temple, and cheek is drawn toward the
medial angle of the orbit, and the eyelids are firmly closed, as in
photophobia. The skin thus drawn upon is thrown into folds, especially radiating
from the lateral angle of the eyelids; these folds become permanent in
senescence, and form the so-called “crow's feet.” The Levator palpebræ
superioris is the direct antagonist of this muscle; it raises the upper eyelid
and exposes the front of the bulb of the eye. In addition, the orbital and
palpebral portions can work independent of each other, as in the furrowing of
the brows by contraction of the orbital to reduce glare while keeping the eyes
open by virtue of the relaxation of the palpebral.
Each time the eyelids are closed through the action of the Orbicularis, the
medial palpebral ligament is tightened, the wall of the lacrimal sac is thus
drawn lateralward and forward, so that a vacuum is made in it and the tears are
sucked along the lacrimal canals into it. The lacrimal part of the Orbicularis
oculi draws the eyelids and the ends of the lacrimal canals medialward and
compresses them against the surface of the globe of the eye, thus placing them
in the most favorable situation for receiving the tears; it also compresses
the lacrimal sac. This part comprises two pieces: Horner's muscle and the
muscle of Riolan, the latter helps hold the eyelids together to keep the
lacrimal passage waterproof. Associated pathology, such as a lesion
of the facial nerve seen in Bell's palsy results in the inability to blink or
close the ipsilateral eyelid. Subsequent lack of irrigation increases the risk of
corneal inflammation and ulcers. Other muscles involved
= Levator palpebrae superior= As well as inactive control from the
orbicularis oculi, the levator superior aponeurosis actively contributes to size
of aperture. It starts at the apex of the orbit as a thin tendon, and broadens
until it reaches the eyelids, between the tarsal plate and the skin. Since it
is connected with other muscles that move the eye proper the eye tends to
move up with the upper eyelid. = Sympathetic=
Both the levator and the orbicularis are striated and voluntary. However, there
are unstriated fibers which are involuntary and of the sympathetic
branch of the autonomic nervous system, which when both contracted, the upper
and lower eyelids are raised and lowered respectively. These widen the palpebral
aperture. Note
It is involved in the cornea reflex. This can be used to examine the facial
nerve even in unconscious patients. = Adjacent facial muscles=
A number of auxiliary muscles assist in cooperating with the eyelid muscles. For
example, the corrugator supercilii pulls the eyebrows to the bridge of the nose,
making a roof over the middle of the forehead and forehead wrinkles, used
mainly to protect the eyes from excess sunlight. The procerus muscles, in the
bridge of the nose, arise from the lower nasal bone to the lower forehead, on
each side of the midline. The procerus muscles pull the skin into horizontal
wrinkles. The frontalis muscle, which runs from the upper forehead, halfway
between the coronal suture and the top edge of the orbit, attaches to the
eyebrow skin. Since it pulls the eyebrows upward, it is the antagonist of
the orbicularis oculi. It is used in looking up, and increasing vision if
there is insufficient light or when objects are far away.
Additional images References
This article incorporates text in the public domain from the 20th edition of
Gray's Anatomy ^ a b c d e f "Eye, Human."Encyclopædia
Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2010
External links PTCentral