Anatomy - Eye, Orbit, and the Visual Pathway

Eyelids

Flexible and mobile multi-layered structures that cover the eye anteriorly. Very thin to allow for rapid excursions of the lids during blinking

Eyelids

Primarily functions to protect the eye from bright light and foreign objects through the action of blinking. Prevents desiccation (drying) of the cornea. Aids in the tear flow from the lacrimal glands and the aspiration of tears into the nasolacrimal system

Medial Commissure

Inner corner where eyelids join

Lateral Commissure

Outer corner where eyelids join

Medial Canthus

Tissues just beyond medial commissure

Lateral Canthus

Tissues just beyond the lateral commissure

Upper Eyelid Crease

Indentation or fold in upper eyelid

Lower Eyelid Margin

Edge of eyelid

Nasojugal Fold

Indentation extending from lid down along the nose

Sclera

White layer of the eyeball

Iris

Colored layer inside of the eyeball

Pupil

Hole in the iris that lets in light

Palpebral Fissure

Opening between the eyelids

Upper Eyelid

Larger and more mobile than the lower eyelid because of the Levator Palpebrae Superioris. Arises above the Annulus of Zinn. Becomes vertical near the Whitnall’s ligament

Whitnall’s Ligament (Superior Transverse)

Acts like a clothesline with orbital structures suspended from it.

Orbital rim

The Whitnall’s Ligament and the Superior Oblique Tendon in the trochlea have common fascial attachments at the?

Ptosis

During manipulation of the Superior Oblique Tendon, the Superior Transverse Ligament (Whitnall’s ligament) may be inadvertently weakened. This can compromise the medial horn of the levator palpebrae superioris muscle, as a result, this occurs.

Lower Eyelid

Associated with the following: Lockwood’s ligament - Analogous to Whitnall’s ligament, Capsulopalpebral fascia - Analogous to the levator aponeurosis

Lockwood’s Ligament

Supports the globe like a hammock, preventing its descent when inferior bony support is lost. If caught in a blowout fracture, it can result in hypoglobus

Palpebral Fissure

Elliptical opening between the eyelids bounded by the upper and lower palpebral margins

Subcutaneous tissue

Layer of the eyelid that is scanty in amount

Cilia

Also known as eyelashes. Short and curved away from the palpebral fissure

Glands of Zeis

Modified sebaceous gland connected with the follicles of the eyelashes. Empty its secretions into the follicles of the eyelashes

Glands of Moll

Sweat glands which secrete sebum. Unbranched sinuous tubules. Empty its secretions into the follicles of the eyelashes

Muscular Layer

Layer of the eyelids that contains muscles that allow for eyelid movement

Orbicularis Oculi

Innervated by facial nerve (CN VII). Paralysis of the orbicularis oculi serves as the major problem in Bell’s Palsy. Responsible for closing the eyes

Palpebral Portion

Part of the orbicularis oculi that is located around the upper and lower eyelid. Arises from the medial palpebral ligament, muscle of facial expression

Orbital portion

Part of the orbicularis oculi that is located around the orbit.

Lacrimal portion

Part of the orbicularis oculi that is located posterior to the lacrimal sac

Levator Palpebrae Superioris

Arises from the apex of the orbit. Acts to draw the lids upwards when the eyeball is elevated. Innervated by the superior division of the oculomotor nerve (CN III). Paralysis produces ptosis or drooping of the eyelid

Superior Tarsal Muscle of Muller

Composed of smooth involuntary muscles. Accentuates the opening of the palpebral fissure under sympathetic stimulation (a.k.a. “wide-eyed fear”)

Pseudoptosis

(slight drooping of the eyelid) will be produced if there is damage to the Tarsal Muscle of Mullee

Lid Retractors

Responsible for opening the eyelids. Sympathetic nerves innervate the smooth muscle components. The levator palpebrae superioris and inferior rectus muscles are supplied by oculomotor nerves (CN III)

Levator Palpebrae Superioris, Superior Tarsal Muscle of Muller

What are the lid retractors of the upper lid?

Inferior Rectus Muscle

What are the lid retractors of the lower lid?

Tenon’s Capsule (Bulbar Sheath)

Layer of fascia that envelops the globe from the limbus to the optic nerve. Forms a connective tissue socket in which the eyeball is suspended. Facilitates the movements of the eyeball

Tarsal glands (Meibomian glands)

Long sebaceous glands in the tarsal plate. Produces sebaceous substance that creates an oily layer (lipid layer) on the surface of the tear film. Prevents rapid evaporation of the normal tear layer

Accessory lacrimal glands of Wolfring

Present near the upper border of the tarsal plate

Palpebral Conjunctiva

Lines the inner surface of each eyelid. Thicker than the bulbar conjunctiva, opaque, and highly vascular. Forms the deepest layer of the eyelid. Thin mucous membrane that is reflected on the sclera of the eyeball. This part keeps the inner eyelids moist and lubricated so they open and close easily without friction or causing eye irritation

Bulbar Conjunctiva

Thin, transparent, and loosely attached to the bulb of the eye. Lies loose over the underlying structures and thus, can be moved easily. Separated from the anterior sclera by episcleral tissue and Tenon's capsule

Marginal Arterial Arcade

Gives rise to: Medial palpebral arteries, Lateral palpebral arteries. Location: Submuscular plane in front of the tarsal plate, Upper lid: 2 mm away from the lid margin, Lower lid: 4mm away from the lid margin

Superior Arterial Arcade

Location: In the upper eyelid, near the upper border of the tarsal plane

Post Tarsal Vein

Drains to the Ophthalmic vein

Pre Tarsal Vein

Drains to the Subcutaneous vein

Submandibular Lymph Nodes

Drains the Median half of the eyelids

Pre-Auricular Lymph Nodes

Drains the Lateral half of the eyelids

Conjunctivitis

Swelling or inflammation of the conjunctiva. Can be due to bacterial, viral or allergic origins

Bacterial

Purulent discharge. Eyes may be ‘stuck together’ in the morning. May or may not have a history of Otitis media. Initial treatment involves self-care, clean discharge using cotton wool soaked in water. Severe or Prolonged (>1 week) treatment involves the use of topical antibiotics such as chloramphenicol (first-line) or fusidic acid

Viral

Serous “Watery Discharge”. Recent Upper Respiratory Tract Infection (URTI). May or may not affect preauricular lymph nodes. Treatment involves reassurance + supportive management

Allergic

Bilateral Redness, Itching, Chemosis (swelling of conjunctiva and, possibly, the eyelids). History of atopy or may be seasonal (due to pollen) or perennial (due to dust mite, washing powder, or other allergens). Treatment involves the use of topical antihistamines (first-line)

Hordeolum

Common disorder of the eyelid. Acute focal infection (usually staphylococcal) involves either the glands of Zeis (external hordeolum or styes) or, less frequently, the Meibomian glands (internal hordeolum).

Chalazion

Cyst in the eyelid due to a blocked oil gland. The blocked gland is usually the Meibomian gland but it can also be the gland of Zeis

Blepharospasm

Any abnormal contraction or twitch of the eyelid. Incidence: Average age: 45-70 years old. More common in women. Affects approximately 300 out of 1 million. Treatment involves medical therapy

Blepharoplasty

Procedure done on the upper eyelids in order to reduce excess skin and fat. Excess skin can hang over the eyelid and interfere with vision. Also known as “eyelift”

Ptosis

Drooping of the eyelid. Caused by third nerve (oculomotor) palsy. Often due to compression by an aneurysm

Entropion

In turning of the eyelids. Caused by a change in the musculature and supporting tissue of the eyelid. Common in old age and at the lower eyelids. May cause corneal ulceration and scarring

Ectropion

Eversion of the eyelids. Caused by weakness in the musculature and supporting tissue of the eyelid. Common in old age and with facial nerve palsy. May cause epiphora (watering of eye)

Lacrimal Gland

Tear-secreting gland. Located in the anterior superior temporal portion. Oval-shaped, 2 cm in size, and consists of several lobes with 6 to 12 excretory ducts. Secretion is slightly alkaline, and it contains a bactericidal enzyme, lysozyme

Lacrimal Puncta

Small opening, 0.5 mm in the lacrimal apparatus

Lacrimal Papilla

Small nipple-like eminence in the lacrimal apparatus

Lacrimal Canaliculus

1mm x 8mm lined by stratified squamous epithelium in the lacrimal apparatus

Lacrimal Sac

Dilated portion that lies in the bony lacrimal fossa. 1 cm (length) and 5 mm (width)

Maier’s Sinus

Dilation prior to lacrimal sac

Valve of Rosenmuller

Prevents reflux from sac into the common canaliculus

Nasolacrimal Duct

Less than 2 cm in length. Downward continuation of the lacrimal sac. Occupies the nasolacrimal canal formed by the maxilla, lacrimal bone and inferior nasal concha

Valve of Hasner

Situated high up in the inferior turbinate. Most common site of obstruction. Most significant fold situated near the meatal opening of the nasolacrimal duct. Prevents air from being blown back from the nose into the nasolacrimal sac

Ciliated Pseudostratified Epithelium

Lines both the lacrimal sac and duct

Lipid, Aqueous, Mucin

A normal tear film is composed of three layers, namely?

Lipid

Top most layer, helps to prevent rapid evaporation. Made by Meibomian glands. Prevents overflow. Prevents skin lipid contamination. Controls evaporation

Aqueous

Middle layer. Made from the main and accessory lacrimal glands. Gas exchange. Antibacterial function. Cleansing. Optical surface enhancement. Lubrication

Mucin

Next to the cornea and allows the tear film to spread over the ocular surface. Made from Goblet cell. Wetting and optical surface enhancement of epithelial tissue. Physical/immunological protection

Epiphora

Subset of “watering eye. Normal tear production but diminished reabsorption. Caused by: Entropion, Ectropion, Blockage Of The Drainage System

Nasolacrimal Duct Obstruction

The valve of Hasner, which is the very end of the nasolacrimal duct, is the most common place for a blockage to occur. Caused by the failure of canalization of the epithelial cells. Common in infants

Aqueous Tear

Caused by Congenital (Riley-Day Syndrome), Acquired (Decongestants, Antihistamines, Diuretics)

Mucin Tear

Caused by Decreased Vitamin A

Lipid Tear

Caused by Trauma to tarsal gland

Frontal, Lacrimal, Zygomatic, Maxillary, Ethmoid, Palatine, Sphenoid

What are the seven bones of the orbit?

Frontal process of maxilla, Lacrimal, Orbital plate of ethmoid, Sphenoid

What are the bones of the medial wall?

Lamina papyracea

The thinnest wall of the orbit is frequently fragmented due to blow-out fractures. Frequently eroded by chronic inflammatory lesions, neoplasms, and cysts. Provides alternate access to the orbit through the adjacent sinus

Frontal process of zygomatic, Greater wing of spehnoid

What are the bones of the lateral wall

Lateral Wall

The thickest and strongest wall of the orbit

Roof of Orbit

Triangular and faces downwards and slightly forward. Underlies the frontal sinus and the anterior cranial fossa

Orbital plate of frontal, Lesser wing of sphenoid

What are the bones of the orbital roof?

Maxilla, Palatine, Orbital Plate of Zygomatine

What are the bones of the orbital floor?

Blow-Out Fracture

The orbital floor, with its thin structure, is involved in this fracture due to the unsupported dome of the maxillary sinus and the weakened infraorbital groove and canal.

Optic Foramen

Leads from the middle cranial fossa to the apex of the orbit. 6.5 mm in diameter. Lesser wing of the sphenoid bone. Conducts the optic nerve, ophthalmic artery, and sympathetic fibers from the carotid plexus

Optic nerve gliomas

Optic foramen enlargement is commonly seen with?

Supraorbital foramen

Medial third of the superior margin of the orbit. Conveys blood vessels and the supraorbital nerve

Orbital nerve block

Often used to accomplish regional anesthesia of the face

Zygomatic foramen

Contains the zygomaticofacial and zygomaticotemporal branches of the zygomatic nerve and the zygomatic artery

Infraorbital foramen

Contains the infraorbital artery, veins, and nerve. Provides a route of spread for infection or maxillary tumors to the orbit and the skull base

Superior Orbital Fissure (SOF)

22 mm in length. Located between the greater and lesser wings of the sphenoid bone. Spanned by the common tendinous wing of the rectus muscle or the annulus of Zinn

Lateral Part of SOF

The following contents of SOF are found on what part: Recurrent branch of ophthalmic artery, Lacrimal nerve, Frontal nerve, Trochlear nerve, Superior ophthalmic vein?

Middle Part of SOF

The following contents of SOF are found on what part: Abducens nerve, Superior division of oculomotor nerve, Nasociliary nerve, Inferior division of oculomotor nerve?

Medial Part of SOF

The following contents of SOF are found on what part: Inferior ophthalmic vein?

Tolosa-Hunt Syndrome

Idiopathic inflammation, specifically involving the superior orbital fissure, results in?

Inferior Orbital Fissure

Lies below the superior fissure between the lateral wall and the floor of the orbit. It transmits the following: Infraorbital and zygomatic branches of the 5th cranial nerve, Infraorbital vessels, Maxillary nerve, Emissary veins

Annulus Tendineus

Also known as the annulus of Zinn. Common tendinous ring of the rectus muscle. Oval, fibrous ring at the apex of the periorbital. Gives rise to the 4 rectus muscles of the eye. The rectus muscle diverges from the annulus tendineus to insert into the sclera of the eyeball

Rectus Muscles

Inserts into the sclera about 6mm behind the margin of the cornea

Medial Rectus

Broadest. Adducts the eye. Innervated by CN III