02/17/16 Orbit and Contents

Retina

Converts focused light into nerve impulses. Light has to pass into the inner retina to reach photoreceptors (Rods and Cones).

Vitreous humour

90% water with collagen fibrils and hyaluronic acid, has a gel-like consistency. Degenerates with increased age. A transparent, colorless, gelatinous mass that fills the space in the eye between the lens and the retina. It is present at birth and remains unchanged throughout one's life.

Posterior ethmoidal nerve

A branch of the nasociliary nerve. It passes through the posterior ethmoidal foramen, with the posterior ethmoidal artery. It carries sensory information from the sphenoid sinus and posterior ethmoidal air cells. It is absent in about 30% of people.

Inferior rectus

A muscle in the orbit of the eye. As with most of the muscles of the orbit, it is innervated by the oculomotor nerve (Cranial Nerve III). Eye movement It depresses, adducts, and helps extort (rotate laterally) the eye. The inferior rectus muscle is the only muscle that is capable of depressing the pupil when it is in a fully abducted position.

Medial rectus

As with most of the muscles of the orbit, it is innervated by the inferior division of the oculomotor nerve (Cranial Nerve III). This muscle shares an origin with several other extrinsic eye muscles, the anulus tendineus, or common tendon. It is the largest of the extraocular muscles and its only action is adduction of the eyeball. Its function is to bring the pupil closer to the midline of the body. It is tested clinically by asking the patient to look medially.

What is the only extraocular muscle that does not originate from the Tendinous ring of Zinn?

Inferior oblique muscle.

Globe of the eye and three layers?

Multilayer structure supported by connective tissue and small muscles. It consists of three layers: 1) Sclera (outer layer) 2) Choroid (middle layer) 3) Cornea 4) Retina (inner layer)

Levator palpebrae superioris

Muscle in the orbit that elevates the superior (upper) eyelid. Originates on the lesser wing of the sphenoid bone, just above the optic foramen. Innervated by the superior division of the oculomotor nerve (Cranial Nerve III). Originates from a single central nucleus which provides innervation bilaterally to both LPS muscles. This is why, when one turns one's eye upward, the eyelid tends to rise with it.

Cornea

Transparent front part of the eye that covers the iris, pupil, and anterior chamber. This part of the eye, along with the anterior chamber and lens, refracts light, with this structure accounting for approximately two-thirds of the eye's total optical power. Anterior clear portion of the sclera. Its stroma is sandwiched in between an outer epithelial layer and an inner endothelial layer. Contains few cells and no blood vessels. Protects inner eye Refracts light into the eye. Surface innervated by V1. Receives nourishment from tears and aqueous humor. Consistently pumps fluid into aqueous humor

Crystalline lens

Transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina.

Lateral foramina of the orbit?

Zygomatico-orbital foramen

Foramina of the medial orbit?

1) Anterior ethmoid foramen 2) Posteroir ethmoid foramen 3) Nasolacrimal canal

Bones in the Roof of the Orbit (2)

1) Frontal 2) Sphenoid (lesser wing)

Foramina of the floor of the orbit?

1) Inferior orbital fissure 2) Infraorbital canal

What are the extraocular muscles?

1) Levator palpebre 2) Superior rectus 3) Superior oblique 4) Medial rectus 5) Inferior rectus 6) Lateral rectus 7) Inferior oblique

Bones in the Floor of the Orbit (3)

1) Maxilla 2) Zygoma 3) Palatine

Bones in the Medial Wall of the Orbit (5)

1) Maxilla (frontal process) 2) Lacrimal 3) Ethmoid (Lamina papryaceae) 4) Sphenoid (lesser wing) 5) Palatine (orbital plate)

Foramina of the posterior of the orbit?

1) Optic canal 2) Superior orbital fissure

Extraocular muscles, origin, insertion, action, and innervation.

1) Superior rectus - Tendinous ring - Superior portion sclerocorneal junction (SCJ) - Rotate globe superiorly - III 2) Lateral rectus - Tendinous ring - Lateral portion SCJ - Rotate globe laterally - VI 3) Medial rectus - Tendinous ring - Medial portion SCJ - Rotate globe medially - III 4) Inferior rectus - Tendinous ring - Inferior portion SCJ - Rotate globe inferiorly - III 5) Superior oblique - Tendinous ring - Posterior to superior portion SCJ - Rotate globe down and out - IV 6) Inferior oblique - Maxilla of orbital floor - Posterior to superior portion of SCJ - Rotate globe up and out III 7) Levator palpebrae superioris - Tendinous ring - Skin of upper eyelid - Elevate upper eyelid - III

Bones in the Lateral Wall of the Orbit (3)

1) Zygoma 2) Frontal (zygomatic process) 3) Sphenoid (greater wing)

Branches of the nasociliary nerve

1) ethmoidal nerves -anterior ethmoidal nerve -posterior ethmoidal nerve 2) infratrochlear nerve 3) long ciliary nerve 3) communicating branch to the ciliary ganglion (long root of the ciliary ganglion) PLICA is a mnemonic often used to remember these branches.

Amacrine cells

Interneurons in the retina. They are named from the Greek roots a- ("non"), makr- ("long") and in- ("fiber"), because of their short neuritic processes. These cells are inhibitory neurons, and project their dendritic arbors to the inner plexiform layer (IPL), there interacting with retinal ganglion cells and/or bipolar cells. These cells with extensive dendritic trees are thought to contribute to inhibitory surrounds by feedback at both the bipolar cell and ganglion cell levels. In this role they are considered to supplement the action of the horizontal cells. Other forms of amacrine cell are likely to play modulatory roles, allowing adjustment of sensitivity for photopic and scotopic vision. This cell can be a mediator of signals from rod cells under scotopic conditions.

Abducens nerve (CN6)

A somatic efferent nerve that, in humans, controls the movement of a single muscle, the lateral rectus muscle of the eye. The abducens nerve carries axons of type GSE, general somatic efferent, which innervate skeletal muscle of the lateral rectus. It leaves the brainstem at the junction of the pons and the medulla, medial to the facial nerve. In order to reach the eye, it runs upward (superiorly) and then bends forward (anteriorly). The nerve enters the subarachnoid space when it emerges from the brainstem. It runs upward between the pons and the clivus, and then pierces the dura mater to run between the dura and the skull through Dorello's canal. At the tip of the petrous temporal bone it makes a sharp turn forward to enter the cavernous sinus. In the cavernous sinus it runs alongside the internal carotid artery. It then enters the orbit through the *superior orbital fissure* and innervates the lateral rectus muscle of the eye.

Supratrochlear nerve and innervation to which areas?

A branch of the frontal nerve, which itself comes from the ophthalmic division of the trigeminal (or fifth) cranial nerve. It is smaller than the nearby supraorbital nerve. It passes above the pulley of the Superior oblique muscle, and gives off a descending filament that joins the infratrochlear branch of the nasociliary nerve. This nerve then exits the orbit between the pulley of the superior oblique and the supraorbital foramen, curves up on to the forehead close to the bone, and ascends beneath the Corrugator supercilii and Frontalis muscles. It then divides into branches which pierce these muscles and supplies the following areas: 1) Skin of the lower part of the forehead, close to the midline. 2) Conjunctiva. 3) Skin of the upper eyelid.

Nasociliary nerve

A branch of the ophthalmic nerve (CN V1; one of three branches of the trigeminal nerve a.k.a CN V). It is intermediate in size between the two other main branches of the ophthalmic nerve, the frontal nerve and the lacrimal nerve, and is more deeply placed. This nerve enters the orbit between the two heads of the lateral rectus muscles and between the superior and inferior rami of the oculomotor nerve (CN III). It passes across the optic nerve (CN II) and runs obliquely beneath the superior rectus muscle and superior oblique muscle to the medial wall of the orbital cavity. It passes through the anterior ethmoidal opening as the anterior ethmoidal nerve and enters the cranial cavity just above the cribriform plate of the ethmoid bone. It supplies branches to the mucous membrane of the nasal cavity and finally emerges between the inferior border of the nasal bone and the side nasal cartilages as the external nasal branch. A branch of the ophthalmic nerve [CN V1] in the superior orbital fissure, passing through the orbit, giving rise to the communicating branch to the ciliary ganglion, the long ciliary nerves, the posterior and anterior ethmoidal nerves, and terminating as the infratrochlear and nasal branches, which supply the mucous membrane of the nose, the skin of the tip of the nose, and the conjunctiva.

Superior oblique

A fusiform muscle originating in the upper, medial side of the orbit (i.e. from beside the nose) which abducts, depresses and internally rotates the eye. It is the only extraocular muscle innervated by the trochlear nerve (the fourth cranial nerve). Origin is the Annulus of Zinn. It loops through a pulley-like structure (the trochlea of superior oblique) and inserts into the sclera on the posterotemporal surface of the eyeball. It is the pulley system that gives superior oblique its actions, causing depression of the eyeball despite being inserted on the superior surface. The primary (main) action of the muscle is intorsion (internal rotation), the secondary action is depression (primarily in the adducted position) and the tertiary action is abduction (lateral rotation).

Trochlear nerve (CN4)

A motor nerve (a somatic efferent nerve) that innervates only a single muscle: the superior oblique muscle of the eye, which operates through the pulley-like trochlea. The trochlear nerve is unique among the cranial nerves in several respects: 1) It is the smallest nerve in terms of the number of axons it contains. 2) It has the greatest intracranial length. 3) It is the only cranial nerve that exits from the dorsal (rear) aspect of the brainstem. 4) It innervates a muscle, Superior Oblique muscle, on the opposite side (contralateral) from its origin.

Lateral rectus

A muscle on the lateral side of the eyeball in the orbit. It is one of six extraocular muscles that control the movements of the eye. This muscle is responsible for lateral movement of the eyeball, specifically abduction. Abduction describes the movement of the eye away from the eyeball, allowing the eyeball to move horizontally in the lateral direction, bringing the pupil away from the midline of the body. Only muscle innervated by the abducens nerve, cranial nerve VI. The abducens nerve exits the brainstem from the pons-medullary junction, and travels through the superior orbital fissure to innervate the lateral rectus muscle.

Anterior ethmoid nerve

A nerve which provides sensory branches to the nasal cavity. The nerve is the continuation of the nasociliary nerve after it enters the anterior ethmoidal foramen into the anterior ethmoidal air cells. The nasociliary nerve arises from the Ophthalmic division of the Trigeminal nerve (CN V) within the orbit. The anterior ethmoidal nerve arises only after the nasociliary has given off its four branches - 1) Ramus communicans to ciliary ganglion, 2) Long ciliary nerves, 3) infratrochlear nerve, 4) Posterior ethmoidal nerve. After branching off of the nasociliary nerve, the _____ ______ nerve enters the anterior ethmoidal foramen and send sensory fibers to the middle and anterior ethmoidal air cells. The _____ _____ nerve then continues into the cranial cavity at the side of the cribiform plate of the ethmoid bone, sends sensory fibers to the meninges, and then enters the nasal cavity via the nasal slit. Within the nose, this nerve gives off sensory fibers to the anterior part of the nasal septum. The branches it gives rise to are called the internal and external nasal branches of the anterior ethmoidal nerve, and the external branch ultimately innervates skin on the lateral sides of the nose.

Zonule of Zinn (Zonule ligaments)

A ring of fibrous strands connecting the ciliary body with the crystalline lens of the eye. These fibers are sometimes collectively referred to as the suspensory ligaments of the lens.

Ciliary body

A ring-shaped thickening of tissue inside the eye that divides the posterior chamber from the vitreous body. It contains the ciliary muscles (which control lens thickness), vessels, and fibrous connective tissue. Folds on the inner ciliary epithelium are called ciliary processes, and these secrete aqueous humor into the posterior chamber. Creates aqueous humour and anchors the lens.

Orbital fat

A semifluid adipose cushion that lines the bony orbit supporting the eye. Selective loss of fatty tissue caused by hormonal imbalances may produce "bulging" of the eye. Traumatic loss of the fat causes a sunken appearance of the eye. Replacement of the fat by tumor or abnormal tissue may be discovered on ophthalmological examination. The examiner gently presses on the front of the eyes through the eyelids. Normally each eye may be displaced 0.5 cm into the socket.

Dilator pupilae

A smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. This muscle consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. These cells are stimulated by the sympathetic nervous system. When stimulated, the cells contract, widening the pupil and allowing for more light to pass through the eye.

What is the innervation for the extraocular muscles?

General Somatic Efferent because these muscles are derived from somites.

Inferior oblique

A thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique is an extraocular muscle, and is attached to the maxillary bone (origin) and the posterior, inferior, lateral surface of the eye (insertion). The inferior oblique is innervated by the inferior branch This muscle arises from the orbital surface of the maxilla, lateral to the lacrimal groove. Unlike most of the other extraocular muscles (recti and superior oblique), the inferior oblique muscle does not originate from the common tendinous ring (annulus of Zinn). Passing lateralward, backward, and upward, between the inferior rectus and the floor of the orbit, and just underneath the lateral rectus muscle, the this muscle inserts onto the scleral surface between the inferior rectus and lateral rectus. The inferior oblique is innervated by the inferior division of the oculomotor nerve (cranial nerve III). Primary action is extorsion (external rotation); secondary action is elevation; tertiary action is abduction (i.e. it extorts the eye and moves it upward and outwards). The field of maximal inferior oblique elevation is in the adducted position. This muscle is the only muscle that is capable of elevating the eye when it is in a fully adducted position.

Inferior opthalmic vein

A vein begins in a venous net-work at the forepart of the floor and medial wall of the orbit; it receives some vorticose veins and other veins from the Rectus inferior, Obliquus inferior, lacrimal sac and eyelids, runs backward in the lower part of the orbit lying above the inferior rectus and divides into two branches. One of these passes through the inferior orbital fissure and joins the pterygoid venous plexus, while the other enters the cranium through the superior orbital fissure and ends in the cavernous sinus, either by a separate opening, or more frequently in common with the superior ophthalmic vein.

Superior opthalmic vein

A vein that begins at the inner angle of the orbit in a vein named the nasofrontal which communicates anteriorly with the angular vein; it pursues the same course as the ophthalmic artery, and receives tributaries corresponding to the branches of that vessel. Near the medial angle of the eye, nose and lips (known as the danger triangle of the face) usually drain through the facial vein, via the ophthalmic vein through the cavernous sinus. As a result, an infection of the face may spread to the cavernous sinus and pterygoid venous plexus. This can lead to damage of the nerves running through the cavernous sinus.

Posteroir ethmoidal artery

An artery of the head which supplies the nasal septum. It is smaller than the anterior ethmoidal artery. Once branching from the ophthalmic artery, it passes between the upper border of the medial rectus muscle and superior oblique muscle to enter the posterior ethmoidal canal. It exits into the nasal cavity to supply posterior ethmoidal cells and nasal septum; here it anastomoses with the sphenopalatine artery. There is often a meningeal branch to the dura mater while it is still contained within the cranium. This artery supplies the posterior ethmoidal air sinuses, dura mater of the anterior cranial fossa, and the upper part of the nasal mucosa of the nasal septum.

Anterior ethmoidal artery

An artery of the head, which branches from the ophthalmic artery and accompanies the nasociliary nerve through the anterior ethmoidal canal to supply the anterior and middle ethmoidal cells, frontal sinus, and anterosuperior aspect of the lateral nasal wall. When entering the cranium, it gives off: 1) a meningeal branch to the dura mater. 2) nasal branches. These descend into the nasal cavity through the slit by the side of the crista galli, and, running along the groove on the inner surface of the nasal bone, supply branches to the lateral wall and septum of the nose, and a terminal branch which appears on the dorsum of the nose between the nasal bone and the lateral cartilage

Lacrimal artery

An artery that arises close to the optic foramen, and is one of the largest branches derived from the ophthalmic artery. Not infrequently it is given off before the artery enters the orbit. It accompanies the _______ nerve along the upper border of the lateral rectus and supplies the ______ gland.

Superior rectus muscle

Muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve (Cranial Nerve III). In the primary position (looking straight ahead), the superior rectus muscle's primary function is elevation, although it also contributes to intorsion and adduction.

Infratrochlear nerve

Nerve given off from the nasociliary nerve just before it enters the anterior ethmoidal foramen. It runs forward along the upper border of the medial rectus, and is joined, near the pulley of the superior oblique, by a filament from the supratrochlear nerve. It then passes to the medial commissure of the eye, and supplies the skin of the upper eyelids and bridge of the nose, the conjunctiva, lacrimal sac and caruncle. From the Trigeminal Nerve CN5 opthalmic division V1.

Supratrochlear artery

One of the terminal branches of the ophthalmic artery, branches off where the ophthalmic artery travels posterior to the trochlea. It leaves the orbit at its medial angle by piercing the orbital septum with the supratrochlear nerve, and, ascending on the forehead, supplies the integument, muscles, and pericranium, anastomosing with the supraorbital artery, and with the artery of the opposite side.

Sclera

Opaque, fibrous, protective, outer layer of the eye containing collagen and elastic fiber. Outer layer of the eye. Collagenous and mostly avascular and acellular. Tough yet thin (~ 1mm). Provides attachment for muscles. Perforated by the optic nerve and opthalamic vessels.

Macula lutea

Oval-shaped pigmented area near the center of the retina of the human eye. It has a diameter of around 5.5 mm (0.22 in). It is subdivided into the umbo, foveola, foveal avascular zone (FAZ), fovea, parafovea, and perifovea areas. After death or enucleation (removal of the eye) the macula appears yellow, a color that is not visible in the living eye except when viewed with light from which red has been filtered.

Cribiform plate

Projecting upward from the middle line of this plate is a thick, smooth, triangular process, the crista galli, so called from its resemblance to a rooster's comb. The long thin posterior border of the crista galli serves for the attachment of the falx cerebri. Its anterior border, short and thick, articulates with the frontal bone, and presents two small projecting alae (wings), which are received into corresponding depressions in the frontal bone and complete the foramen cecum. Its sides are smooth, and sometimes bulging from presence of a small air sinus in the interior. It supports the olfactory bulb and is perforated by foramina for the passage of the olfactory nerves. The foramina in the middle of the groove are small and transmit the nerves to the roof of the nasal cavity; those at the medial and lateral parts of the groove are larger—the former transmit the nerves to the upper part of the nasal septum, the latter those to the superior nasal concha.

Lacrimal gland (sans innervation)

Red, almond-shaped glands, one for each eye, that secrete the aqueous-layer of the tear film. They are situated in the upper-outer portion of each orbit, in the ______ fossa of the orbit formed by the frontal-bone. Inflammation of the ______-glands is called dacryoadenitis. The ______-gland produces tears which then flow into canals that connect to the _______ sac. From that sac, the tears drain through the ______ duct into the nose.

Tendinous ring of Zinn / Annulus of Zinn (Which muscles originate from here?)

Ring of fibrous tissue surrounding the optic nerve at its entrance at the apex of the orbit. It is the origin for five of the seven extraocular muscles, omitting the inferior oblique muscle. 1) Levator palpebrae superioris 2) Superior rectus 3) Medial rectus 4) Lateral rectus 5) Superior oblique

Fovea centralis

Small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina. Responsible for sharp central vision (also called foveal vision), which is necessary in humans for activities where visual detail is of primary importance, such as reading and driving.

Lacrimal nerve

Smallest of the three branches of the ophthalmic division of the trigeminal nerve. It provides sensory innervations for the lacrimal gland, conjunctiva, and the lateral upper eyelids. It passes forward in a separate tube of dura mater, and enters the orbit through the narrowest part of the superior orbital fissure. In the orbit it runs along the upper border of the lateral rectus, with the lacrimal artery, and communicates with the zygomatic branch of the maxillary nerve. It enters the lacrimal gland and gives off several filaments, which supply sensory innervation to the gland and the conjunctiva. Then, it pierces the orbital septum, and ends in the skin of the upper eyelid, joining with filaments of the facial nerve.

Foramina of the roof of the orbit?

Supraorbital notch / foramen

Frontal nerve

The largest branch of the ophthalmic nerve(V1), and may be regarded, both from its size and direction, as the continuation of the nerve. It enters the orbit through the superior orbital fissure, not running within the tendinous ring, and runs forward between the Levator palpebræ superioris and the periosteum. Midway between the apex and base of the orbit it divides into two branches, supratrochlear nerve and supraorbital nerve. It provides the sensory innervations for the skin of the forehead, mucosa of frontal sinus, and the skin of the upper eyelid via General Somatic Afferent (GSA) fibers.

Lacrimal gland innervation

The parasympathetic-nerve supply originates from the _______ nucleus of the facial nerve in the pons. From the pons nucleus-preganglionic-parasympathetic fibres run in the nervus intermedius (small-sensory root of facial nerve) to the geniculate ganglion but they do not synapse there. Then, from the geniculate ganglion, the preganglionic-fibres run in the greater petrosal nerve (a branch of the facial nerve) which carries the parasympathetic-secretomotor fibers through the foramen lacerum, where it joins the deep petrosal nerve (which contains postganglionic-sympathetic fibers from the superior-cervical ganglion) to form the nerve of the pterygoid canal (vidian nerve) which then traverses through the pterygoid canal to the pterygopalatine ganglion. Here, the fibers synapse and postganglionic-fibers join the fibers of the maxillary nerve. In the pterygopalatine-fossa itself, the parasympathetic-secretomotor fibers branch off with the zygomatic nerve and then branch off again, joining with the _______-branch of the ophthalmic-division of CN V, which supplies sensory-innervation to the _______-gland along with the eyelid and conjunctiva.

Choroid layer of eye

The vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. The human _____ is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm. It provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, this structure forms the uveal tract.

Uvea

The vascular middle layer of the eye, which consists of the iris , ciliary body and choroid.

Iris

Thin, circular structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina. The eye color is defined by the color of this structure. Dilation - sympathetic control. Constriction - parasympathetic control. Pigment - controls intra- ocular light scatter.