Term Paper on Orbit | Human Skull | Skeletal System | Biology

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Term Paper on Orbit:

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Term Paper # 1. Anatomical Structure of Orbit:

Orbit is paired pyramidal cavities situated one on each side of the root of nose. Each orbit lodges one eyeball and its associated structures.

Parts:

i. Base

ii. Apex

iii. Medial walls are parallel to each other

iv. Lateral walls are at right angle to each other

v. Roof

vi. Floor.

i. Base:

Base is formed by orbital margin.

Superiorly- Frontal bone has a notch or foramen supra orbital notch or foramen.

Laterally- Zygomatic bone and frontal bone.

Medially- Maxilla and frontal bone.

Inferiorly- Zygomatic and maxilla bone.

ii. Apex:

It is formed by superior orbital fissure.

iii. Medial Wall:

Formed by:

a. Formed by frontal process of maxilla.

b. Lacrimal bone.

c. Ethmoid bone (labyrinth).

d. Body of sphenoid.

Lacrimal fossa presents in it and lodges lacrimal sac.

iv. Lateral Wall:

Formed by:

a. Zygomatic bone.

b. Greater wing of sphenoid

Whitnall’s tubercle present along its anterior part it gives attachment to lateral check ligament.

Suspensary ligament of lock wood – Lateral palpebral raphe.

Levator palpebrae superioris.

Inferior orbital fissure present between floor and lateral wall.

Superior orbital fissure present between roof and lateral wall.

v. Roof:

Orbital surface of frontal bone.

Lesser wing of sphenoid.

Laterally lacrimal fossa is present which lodges lacrimal gland.

vi. Floor:

Orbital surface of maxilla, zygomatic bone, greater wing of sphenoid and orbital process of palatine bone.

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Term Paper # 2. Relations of Orbit:

Superiorly – Anterior cranial fossa

Inferiorly – Maxillary air sinus

Medially – Ethmoidal air sinuses

– Sphenoid air sinus

Laterally – Temporal fossa

– Middle cranial fossa

Openings in the Orbit:

1. Anteriorly it opens on the face.

2. Posteriorly, through infra orbital groove- via inferior orbital fissure opens into pterygo palatine fossa. Infra orbital nerve and vessels along with an emissary vein pass through it.

3. Superior orbital fissure- This opens into middle cranial fossa.

It is divided into three parts by a common tendinous ring:

(a) Supero Lateral Compartment:

This is lateral to ring and transmits lacrimal nerve, trochlear nerve, frontal nerve, superior ophthal­mic vein and recurrent meningeal artery.

(b) Intermediate Compartment:

(Within the ring) it transmits upper and lower divisions of oculomotor nerve (IIIrd nerve), nasociliary nerve (V₁) and abducent nerve.

(c) Infero Medial Compartment:

This lies medial to ring and transmits inferior ophthalmic vein.

4. Optic foramen- This opens into cranial cavity, transmits optic nerve (IInd) and ophthalmic artery.

5. Zygomatico temporal and facial foramina- This transmits zygomatico temporal and facial nerve and vessels.

6. Anterior and posterior ethmoidal foramina- This transmits anterior and posterior ethmoidal nerve and vessels.

7. Medial wall has fossa for lacrimal sac via naso lacrimal duct it opens into nasal cavity.

Eyelids or Palpebrae:

Eyelids are movable curtains found in front of the eye. The upper eyelid is longer and more movable than the lower eyelid. The space between two eyelids is known as palpebral fissure. The eyelids meet along the lateral and medial angles of the eye.

The lower border of the upper eyelid crosses the upper border of the cornea. The deep surface of the eyelids is lined by the conjunctiva. When the eyelids are separated the conjunctival sac is open. When the lids are closed the conjunctival sac is a closed sac or chamber.

Features on Eyelids:

When eyes are open few things are noted:

1. Lacrimal Caruncle:

A small triangular space in the medial part called Lacus Lacrimalis – with a reddish, fleshy elevation in the centre – called lacrimal caruncle.

2. Plica Semilunaris:

A small semilunar fold of conjunctiva present lateral to lacrimal caruncle.

3. Margins of Eyelids:

These are divided into two parts:

(a) Ciliary Part:

This is lateral 5/6th part and is flat having eyelashes or cilia.

(b) Lacrimal Part:

This is medial 1/6th part and is smooth devoid of eyelids.

4. Lacrimal Papilla:

At the junction of these two parts of eyelid margin, there is a small conical projection called lacrimal papilla. On the summit of papilla a small aperture is present known as Lacrimal Punctum.

5. Tarsal Glands:

On the inner surface of eyelids – a number of yellowish parallel streaks of tarsal glands are seen whose ducts open on the posterior margin of the eyelids. The cilia project from the anterior edge.

Layers of Eyelids:

1. Skin:

Skin is the outer layer, thin and loosely attached to underlying tissue. At lower and outer border hairs are arranged in two or more rows. Along the roots of hair there are sebaceous glands called Zeis glands are present. The lid margin has well developed sweat glands called gland of Moll.

2. Superficial Fascia:

This is almost devoid of fat and contains loose areolar tissue.

3. Muscular Layer:

It is formed by orbicularis oculi (sphincter) and palpebral part of Muller muscle is found in both eyelids. But levator palpebrae superioris is found only in the upper eyelid, this is called opener of the eye.

4. Orbital Septum:

It is made up of fibrous membranous sheath attached to the upper and lower borders of the orbital margin. It is thickened anteriorly and forms tarsal plate.

Laterally it is connected by the lateral palpebral ligament and medially by medial palpebral ligament. Borders of the tarsal plate contain 30 to 40 sebaceous glands known as Meibomian glands which lie in grooves on the deep surface of the tarsal plates parallel to each other in a single row.

Palpebral fascia is a layer of connective tissue attached to the orbital margins and extending into the eyelids to become continuous with the tarsus.

5. Conjunctiva:

It is made up of non-keratinized stratified squamous epithelium and is transparent vascular mucous membrane. It lines the upper surface of the lower eyelid and lower surface of the upper eyelid. At the fornices conjunctiva is reflected over the front of eye (sclera) and extends upto the corneal margin.

Nerve Supply:

1. Upper eyelid is supplied by branches of lacrimal, supra orbital, supratrochlear and infra trochlear nerves.

2. Lower eyelid is supplied by palpebral branch of infra orbital nerve.

3. Same nerves supply the conjuctiva that lines each eyelid.

Blood Vessels:

Both eyelids are supplied by palpebral branches of the ophthalmic artery. Lower eyelid has an additional supply by palpebral branch of infra orbital artery.

Veins:

Follow the course of arteries and drains into superior and inferior ophthalmic veins and infra orbital vein.

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Term Paper # 3. Lymphatic Drainage of Orbit:

Lateral part of eyelids drain into preauricular lymphnodes and medial part of lids drain into buccal and submandibular group of lymph nodes.

Applied Anatomy:

1. Blepharitis:

Chronic inflammation of the eyelid margins.

2. Stye (Hardeolum Externum):

Acute inflammation of the lid margin and glands of hair follicles, i.e., Zeis glands.

3. Chalazion:

It is a chronic granulomatous inflammation of the Meibomian gland (Tarsal glands).

4. Entropeon:

Inward tilting of the eyelid margins along with eye lashes (inversion).

5. Ectropion:

It is the eversion of the lid margin.

6. Ptosis:

This may be congenital or acquired drooping of the upper eyelid due to paralysis of the levator palpebrae superioris.

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Term Paper # 4. Contents of Orbit:

1. Eyeball

2. Extra ocular muscles of eyeball

3. Lacrimal apparatus

4. Orbital fascia

5. Ophthalmic artery and its branches

6. Superior and inferior ophthalmic veins

7. Central vein of retina

8. Ciliary ganglion

9. Nerves of the orbit

10. Lymphatics of the orbit. 

1. Eyeball:

Anterior 1/6th is cornea which is transparent, posterior 5/6th is sclera – which is opaque made up white fibrous sheath.

Antero posterior diameter is 24 mm.

Optic nerve enters through optic disc – which lies 3 mm medial to posterior pole.

Macula lies on posterior pole and has maximum visual acuity due to collection of cones in the retina.

2. Extra Ocular Muscles or Muscles of the Orbit:

Within the orbit there are four recti, two oblique and one levator palpebrae superioris are situated.

Recti muscles are:

(a) Superior rectus

(b) Inferior rectus

(c) Medial rectus and

(d) Lateral rectus.

All Rectus Muscles:

Originate from the common tendinous ring, which is situated around the superior, medial and inferior borders of the optic foramen.

Origin:

Superior rectus arises from upper part of the common tendinous ring.

Inferior rectus arises from lower part of ring.

Medial rectus arises from medial part of the ring.

The lateral rectus arises by two heads – one from the upper and one from the lower aspect of the lateral part of the common tendinous ring.

Following structures are passing between the two heads of the lateral rectus:

(1) Upper and lower divisions of oculomotor nerve.

(2) Nasociliary nerve.

(3) Abducent nerve.

From the origin recti muscles widen forwards and form the cone of muscles.

Insertion:

They are inserted to the corresponding surface of the sclera, behind the corneal margin at the various distances, ranging from 6.5 mm to 8 mm away.

Nerve Supply:

Superior rectus is supplied by upper division of oculomotor nerve.

Medial rectus and inferior rectus are supplied by inferior division of oculomotor nerve.

The lateral rectus is supplied by the abducent nerve.

Action:

Lateral rectus moves the cornea horizontally and laterally.

Medial rectus moves the cornea horizontally and medially.

Superior rectus moves the cornea upwards and slightly medially.

Inferior rectus moves the cornea downwards and slightly medially.

Superior Oblique Muscle of Orbit:

Origin:

It arises from orbital surface of the body of sphenoid bone above and medial to optic foramen and inferior surface of lesser wing of sphenoid bone.

Course and Insertion:

Superior oblique muscle forms a tendon, which winds round the fibro cartilagenous pulley like trochlea and expands for insertion on the upper surface of the sclera, which lies below the insertion of superior rectus muscles, and behind the equator.

Nerve Supply:

Nerve supply is by trochlear nerve, i.e., 4th cranial nerve.

Action:

It rotates the eyeball downwards and laterally.

Inferior Oblique Muscle:

Origin:

It arises from upper surface of floor of the orbit, lateral to the lacrimal groove.

Insertion:

On lateral surface of the sclera behind the equator.

Action:

It rotates the eyeball – upwards and laterally.

3. Lacrimal Apparatus:

It is formed by lacrimal gland and its drainage system.

For example- Lacrimal gland, Lacrimal ducts, Conjunctival sac, Lacrimal puncta, Lacrimal canaliculi , Lacrimal sac, Naso lacrimal duct.

i. Lacrimal Gland:

It is situated on the antero lateral aspect of the roof of the orbit. The gland is ‘J’ shaped.

Type:

Compound recemose type of serous gland.

The aponeurosis of the levator palpebrae superioris divides the gland into a large deeper orbital part, and a small palpebral part is superficial, lying within the eyelid.

The two parts are continuous with each other around the lateral aspect of the aponeurosis. The ducts of the orbital part pass through the palpebral part and opens into the lateral part of superior conjunctival fornix. There are about 8-10 ducts.

Blood Supply:

Lacrimal artery a branch of ophthalmic artery supplies the lacrimal gland.

Nerve Supply:

1. Lacrimal nerve is sensory for the gland and is branch of ophthalmic division of trigeminal nerve (Vth).

2. Parasympathetic supply comes from – Lacrimatory nucleus situated in the pons. Pre­ganglionic fibres pass through geniculate ganglion of facial nerve → greater superficial petrosal nerve → joins deep petrosal nerve (sympathetic) → to form the nerve of pterygoid canal → relayed into pterygo palatine ganglion → post ganglionic fibres join maxillary nerve → zygomatic nerve → zygomatico temporal nerve → parasympathetic fibres leave and joins lacrimal nerve → reaches to lacrimal gland and are secretomotor for the gland.

Functions of the Tears:

1. Keeps the cornea and front of the eyeball moist.

2. Removes the foreign bodies from the surface of the eye.

3. Lacrimal fluid contains enzymes called lysozymes.

4. It has bacterio static function.

Accessory lacrimal glands (Glands of Krause) are situated along the fornices of the conjunctival sac.

ii. Conjunctival Sac:

This is the space between the inner surface of the eyelids and anterior surface of eyeball. When lids are closed the sac is a closed space.

iii. Lacrimal Canaliculi:

It commences from the lacrimal punctum.

Each duct is 10 mm long.

The upper canaliculus is directed upwards and medially, it then dilates, form an ampulla and then directed downwards and medially to open into the lacrimal sac.

The inferior canaliculus passes downwards and then horizontally and medially to open into the lacrimal sac behind the medial palpebral ligament.

Some-times superior and inferior canaliculi may unite to form the sinus of Meir which opens into the lacrimal sac.

iv. Lacrimal Sac:

It is a membranous sac, about 12 mm long and 5 mm wide, situated in the lacrimal fossa or groove behind the medial palpebral ligament. Its upper end is blind and lower end is continuous with the nasolacrimal duct.

The sac is covered by the lacrimal fascia derived from the orbital perioteum. Between the fascia and sac a venous plexus is present.

Relations:

Anterior:

a. Medial palpebral ligament.

b. Anterior lacrimal crest giving origin to orbicularis oculi.

Posterior:

Lacrimal part of the orbicularis oculi is attached.

Laterally:

Lacrimal fascia and lacrimal part of orbicularis oculi.

Medially:

Lacrimal groove separates it from the nose.

Applied:

Inflammation of the lacrimal sac is called dacrocystitis.

v. Naso Lacrimal Duct:

It is a membranous passage about 18 mm long. It extends from lacrimal sac to the inferior meatus of the nose, runs downwards, backwards and laterally.

The terminal part of the duct is oblique. The opening is guarded by a mucous valve called Hasner’s valve. It prevents entry of air into the sac.

Lacrimal Circulation:

The watery lacrimal fluid secreted by the gland flows into the conjuctival sac where it lubricates the front of the eye and deep surface of the lids. Periodic blinking helps to spread the fluid over the eye. Most of the fluid evaporates; rest is drained by the lacrimal canaliculi. When excessive it overflows as tears. Through the canaliculi it reaches the sac. From the lacrimal sac via naso lacrimal duct the tears drip into the inferior meatus of the nose.

Applied Anatomy:

i. Epiphora:

Over flow of tears on the cheek due to excessive secretion or obstruction of lacrimal passage.

ii. Acute Dacryo Adenitis:

Acute inflammation of the lacrimal gland.

iii. Dacryo Cystitis:

Inflammation of lacrimal sac due to obstruction of the naso lacrimal duct.

4. Orbital Fascia:

Thick fascia derived from periosteum of orbital bones. This extends from sclero corneal junction to the entry of the optic nerve on the back.

Orbital fascia is loosely attached to sclera. It forms the socket for eyeball in which eyeball moves. Inferiorly it becomes thick and forms the suspensory ligament of Lockwood.

Tendons of ocular muscles pierce the capsule and are attached to sclera.

A sleeve of fascia is continued over muscles as facial sheath.

Where medial and lateral recti pierce the fascia it forms strong check ligaments which are attached to Whitnall’s tubercle laterally and a posterior compartment lodges the retrobulbar structures.

5. Ophthalmic Artery and Its Branches:

It is a branch of internal carotid artery arises within the middle cranial fossa.

Course:

It runs forwards and enters the optic canal. It lies infero lateral to the optic nerve and enters the orbit. It crosses superior to the optic nerve from lateral to medial side, accompanied by the naso-ciliary nerve and superior ophthalmic vein. It reaches the medial side of the orbit and terminates by dividing into supratrochlear and dorsal nasal branches.

Branches:

i. Muscular Branches:

To supply extrinsic muscles of the eyeball.

ii. Central Artery of Retina:

It is an end artery, arises from the ophthalmic artery when it comes medial to optic nerve. It pierces the postero­medial aspect of the optic nerve about 1 cm behind the eyeball and runs forwards enters the retina and divides into temporal and nasal branches. It supplies the optic nerve and retina.

iii. Two Long Posterior Ciliary Arteries:

To supply eyeball.

iv. About Seven Short Posterior Ciliary Arteries:

To supply the choroids and outer layers of the retina.

v. Lacrimal artery supplies lacrimal gland and eyelids.

It gives a pair of lateral palpebral arteries to supply each eyelid. They anastomose with medial palpebral arteries.

It also gives a recurrent meningeal branch – passes through superior orbital fissure and anastomoses with anterior branch of middle meningeal artery and supply meninges of middle cranial fossa.

vi. Posterior Ethmoidal Artery:

Supplies posterior ethmoidal and sphenoidal air sinus and nose.

vii. Anterior Ethmoidal Artery:

Supplies nose, anterior and middle ethmoidal air sinuses.

viii. Medial Palpebral Arteries:

These anastomoses with lateral palpebral branches.

ix. Supra Orbital and Supra Trochlear Arteries:

Supplies forehead and scalp.

x. Dorsal Nasal Artery:

Supplies dorsum of the nose and ends by anastomosing with the branches of facial artery.

6. Ophthalmic Veins:

There are two ophthalmic veins:

(A) Superior Ophthalmic Vein:

It begins along the medial aspect of upper eyelid, crosses superior to optic nerve from medial to lateral side, accompanied by ophthalmic artery and naso ciliary nerve. It passes through superior orbital fissure and terminates into cavernous sinus.

Tributaries:

These are small veins accompanying the branches of the ophthalmic artery joins and form superior ophthalmic vein.

(B) Inferior Ophthalmic Vein:

It is situated along the floor of the orbit. It drains orbital muscles, lacrimal sac and eyelids etc. It terminates by draining into cavernous sinus, passing through medial part of superior orbital fissure.

Applied Anatomy:

Facial vein is communicated with the superior ophthalmic vein. So infections from face spread via superior ophthalmic vein to cavernous sinus causing thrombosis of the sinus.

7. Central Vein of Retina:

It joins the superior ophthalmic vein or separately drains into cavernous sinus.

8. Ciliary Ganglion:

It is situated near the apex of the orbit on the lateral side of optic nerve, medial to lateral rectus. It is a peripheral parasympathetic ganglion.

Size:

Pin head – 2 mm

Topographically it is connected to naso ciliary nerve.

Functionally connected to oculomotor nerve.

Structure:

Multipolar neurons present in it.

Roots:

i. Motor Root:

Comes from nerve to inferior oblique. This is a parasympathetic root – to supply sphincter pupillae and ciliaris muscle. Preganglionic fibres come from Edinger Westphal nucleus and relayed in the ganglion. Post ganglionic fibres arise and pass through short ciliary nerves.

ii. Sensory Root:

Comes from naso ciliary nerve. It contains sensory fibres from eyeball.

iii. Sympathetic Root:

Comes from internal carotid plexus to supply – dialator pupillae. These are post ganglionic fibres coming from superior cervical sympathetic ganglion.

Branches:

15 to 20 short ciliary nerves arise from the ganglion to supply ciliary body muscles and muscles of the iris, i.e., Sphincter and dilator pupillae. These nerves pierce the sclera around the entrance of the optic nerve, containing fibres from all the three roots of the ganglion.

9. Nerves of the Orbit:

These are optic nerve, oculomotor nerve, trochlear nerve, branches of ophthalmic and maxillary divisions of the trigeminal, abducent nerve and sympathetic nerves.

(a) Optic Nerve:

Optic nerve is the nerve of sight and 2nd cranial nerve, made up of axons, i.e., central processes of the ganglionated cell layer of the retina. It pierces the choroids and sclera at lamina cribrosa, situated 3 or 4 mm medial to the posterior pole of the eyeball.

The nerve passes through the retrobulbar compartment of the orbit, enters the optic canal through the optic foramen and reaches the anterior cranial fossa. It terminates by joining the nerve of the opposite side and forms the optic chiasma.

Length is about 40 mm.

Parts:

a. Intra orbital part – 25 mm long

b. Part within the optic canal – 5 mm long

c. Intra cranial part – 10 mm long.

Blood Supply:

a. Central artery of retina

b. Superior hypophyseal artery

c. Branches of ophthalmic artery.

Venous drainage by central vein of retina drains into cavernous sinus.

(b) Oculomotor Nerve:

It is the 3rd cranial nerve has motor and parasympathetic fibres. It enters in the orbit as upper and lower divisions within the common tendinous ring. It supplies extra ocular muscles except superior oblique and lateral rectus muscle. Para­sympathetic fibres supply ciliaris muscle and sphincter puplae muscles which helps in accommodation. These fibres are relayed into ciliary ganglion.

(c) Trochlear Nerve:

It is the fourth cranial nerve; motor in nature, supply only superior oblique muscle enters the orbit through lateral compartment of superior orbital fissure passes upwards medially.

(d) Abducent Nerve:

Is the sixth cranial nerve, motor in function, supply only lateral rectus muscle, and enters the orbit within the common tendinous ring, i.e., intermediate compartment of superior orbital fissure.

(e) Ophthalmic Division of Trigeminal Nerve:

It is one of the branches of 5th cranial nerve. Pure sensory, divides into frontal, lacrimal and nasociliary nerves, enters into the orbit through superior orbital fissure to supply – scalp, lacrimal gland, eyelids, eyeball conjunctina, ethmoidal and sphenoidal air sinues and nose.

9. Lymphatics of the Orbit:

Drains into preauricular parotid lymph nodes.

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