Head and Neck: Special Organs of the Head (Eyes)

What is the overall shape and orientation of the Orbit?

Pyramidal cavity with base anterior and apex posterior

Which bone forms the Superior margin of the Orbit?

Frontal bone

Which bones form the Lateral margin of the Orbit?

Processes of frontal and zygomatic bones

Which bones form the Inferior margin of the Orbit?

Zygomatic bone and maxilla

Which bones form the Medial margin of the Orbit?

Processes of maxilla and frontal bone

Which bones form the Roof / Superior wall of the Orbit?

Orbital plate of frontal bone and lesser wing of sphenoid

Which bones form the Lateral wall of the Orbit?

Zygomatic bone and greater wing of sphenoid

Which bones form the Floor / Inferior wall of the Orbit?

Orbital plate of maxilla, zygomatic and palatine bones

Which bones form the Medial wall of the Orbit?

Frontal process of maxilla, lacrimal bone, orbital plate of ethmoid, and body of sphenoid

What is transmitted through the Orbital Opening / Notch?

Eyeball

What structure passes through the Supraorbital Foramen?

Supraorbital nerve

What structure passes through the Infraorbital Groove and Canal?

Infraorbital nerve

What structure passes through the Nasolacrimal Canal?

Nasolacrimal duct

What structure passes through the Anterior Ethmoidal Foramina?

Anterior ethmoid nerve (from Ophthalmic division of CN V)

What structure passes through the Posterior Ethmoidal Foramina?

Posterior ethmoid nerve (from Ophthalmic division of CN V)

What structures pass through the Zygomaticotemporal Foramina?

Zygomaticotemporal nerve (from Maxillary)

What structures pass through the Zygomaticofacial Foramina?

Zygomaticofacial nerve (from Maxillary)

What structures pass through the Inferior Orbital Fissure?

Maxillary nerve and its infraorbital and zygomatic branches; Inferior ophthalmic vein and sympathetic nerves

What structures pass through the Superior Orbital Fissure?

Oculomotor, Trochlear, Abducens nerves, Ophthalmic nerve, Superior ophthalmic vein

What structures pass through the Optic Canal?

Optic nerve and Ophthalmic artery

What is the primary action of the Medial Rectus muscle?

Adduction

Which nerve innervates the Medial Rectus muscle?

CN III (Oculomotor nerve)

What is the eye position after injury to the Medial Rectus muscle (or CN III)?

Abducted and Depressed ("Down and Out")

What are the actions of the Superior Rectus muscle?

Elevation; Intorsion; Adduction (Upward and Medial)

Which nerve innervates the Superior Rectus muscle?

CN III (Oculomotor nerve)

What are the actions of the Inferior Rectus muscle?

Depression; Extorsion; Adduction (Downward and Medial)

Which nerve innervates the Inferior Rectus muscle?

CN III (Oculomotor nerve)

What are the actions of the Inferior Oblique muscle?

Extorsion; Elevation; Abduction (Upward and Lateral)

Which nerve innervates the Inferior Oblique muscle?

CN III (Oculomotor nerve)

What are the actions of the Superior Oblique muscle?

Intorsion; Depression; Abduction (Downward and Lateral)

Which nerve innervates the Superior Oblique muscle?

CN IV (Trochlear nerve)

What is the eye position after injury to the Superior Oblique muscle (or CN IV)?

Extorted (slight extorsion or outward rotation of superior eye)

What is the primary action of the Lateral Rectus muscle?

Abduction

Which nerve innervates the Lateral Rectus muscle?

CN VI (Abducens nerve)

What is the eye position after injury to the Lateral Rectus muscle (or CN VI)?

Adducted (Medial deviation or ESOTROPIA)

What are the actions of the Levator Palpebrae Superioris muscle?

Retracts and Elevates Upper Eyelid

Which nerve innervates the Levator Palpebrae Superioris muscle?

CN III (Oculomotor nerve)

What clinical deficit occurs in Levator Palpebrae Superioris injury?

Complete upper eyelid ptosis

What is the general rule for Extraocular Muscle Innervation?

ALL supplied by CN III except Superior Oblique by CN IV (SO4) and Lateral Rectus by CN VI (LR6)

What is the memory rule regarding Superior muscles and torsion?

SUPERIOR people do NOT EXTORT (Superior muscles INTORT)

In what lateral direction do Oblique muscles move the eye?

OBLIQUE muscles move the eye OUT (Abduction)

Where is the Oculomotor Nucleus located?

Ventral part of the periaqueductal gray of the midbrain at the level of superior colliculus

Where is the Abducent Nucleus located?

Beneath the facial colliculus in the floor of the 4th ventricle in the caudal pons

Where is the Trochlear Nucleus located?

Ventral border of the periaqueductal gray of the midbrain at the level of inferior colliculus

What compensates for the extorsion seen in Left Trochlear Nerve Palsy?

Tilting of the head

In a patient with Oculomotor nerve paralysis, which movement can he still perform?

Lateral movement of the eyeball (abduction via intact CN VI / Lateral Rectus and intact CN IV / Superior Oblique)

What injury causes Internal Strabismus (Esotropia)?

Injury to Abducens nerve (CN VI)

Where do the lateral 2/3 of the UPPER and LOWER eyelids drain lymphatically?

Superficial Parotid / Pre-auricular Nodes

Where do the MEDIAL parts of the eyelids drain lymphatically?

Submandibular Nodes

A woman with frontal headache, irregular menses, and loss of peripheral vision bilaterally has a tumor compressing what structure?

The crossing fibers of the optic chiasm (bitemporal hemianopsia)

A patient with Right Nasal Hemianopsia has a lesion at what location?

Uncrossed fibers on the right optic chiasm (lateral aspect of optic chiasm)

A 5 y/o child bumping into objects with bilateral peripheral vision defects and pituitary calcifications has a brain tumor originating from what?

Rathke pouch (Craniopharyngioma)

What visual field defect results from a complete lesion of the Right Optic Nerve (Site 1)?

Total loss of vision in the right eye (Monocular vision loss / blindness of R eye)

What visual field defect results from a midline lesion at the Optic Chiasm (Site 2)?

Non-homonymous bitemporal hemianopsia (Bitemporal hemianopsia)

What visual field defect results from a lesion of the Right Optic Tract (Site 3)?

Contralateral (left) homonymous hemianopsia

What visual field defect results from a lesion of the Temporal Lobe / Meyer's Loop (Site 4)?

Superior left homonymous quadrantanopia ("pie in the sky" disorder)

What visual field defect results from a lesion of the Parietal Lobe / Superior Optic Radiation (Site 5)?

Inferior left homonymous quadrantanopia ("pie in the floor" disorder)

What visual field defect results from a lesion of the Geniculocalcarine Tract (Site 6)?

Contralateral (left) homonymous hemianopsia

What visual field defect results from a lesion of the Inferior Bank of the Calcarine Fissure (Site 7)?

Superior left homonymous quadrantanopia with macular sparing

What visual field defect results from a lesion of the Superior Bank of the Calcarine Fissure (Site 8)?

Inferior left homonymous quadrantanopia with macular sparing

What visual field defect results from a lesion involving Both Banks of the Calcarine Fissure (Site 9)?

Contralateral (left) homonymous hemianopsia with macular sparing

What is the primary etiology for a Right Optic Nerve lesion causing monocular vision loss?

Optic neuritis

What is the primary etiology for an Optic Chiasm lesion causing bitemporal hemianopsia?

Pituitary adenoma

What is the primary etiology for a Right Angle of Chiasm lesion causing right nasal hemianopsia?

Aneurysm of Internal Carotid Artery (ICA)

What is the primary etiology for a Right Optic Tract lesion causing contralateral homonymous hemianopsia?

Vascular lesion

What is the primary etiology for a lesion of the Inferior Optic Radiation (Meyer's loop)?

Temporal lobe lesion

What is the primary etiology for a lesion of the Superior Optic Radiation (Parietal pathway)?

Parietal lobe lesion

What portion of the eye is formed by the Sclera, and what is its tissue composition?

Opaque, vascular posterior five-sixths of the eye; dense connective tissue with type I collagen

What portion of the eye is formed by the Cornea?

Transparent, avascular anterior one-sixth of the eye

What are the 5 distinct layers of the Cornea from outer to inner?

1. Corneal epithelium, 2. Bowman membrane, 3. Stroma, 4. Descemet membrane, 5. Endothelium

What is the histological type of the Corneal Epithelium?

Stratified squamous

What is the nature of Bowman Membrane in the cornea?

Epithelial basement membrane

What is the composition and resident cell type of the Corneal Stroma?

Thickest corneal layer composed of collagen and keratocytes

What is the nature of Descemet Membrane in the cornea?

Endothelial basement membrane

What is the histological type of the Corneal Endothelium?

Simple squamous

What is the memory mnemonic for the layers of the cornea from outer to inner?

"ABCDE": Anterior epithelium, Bowman membrane, Corneal stroma, Descemet membrane, Endothelium

What are Keratocytes vs. Keratinocytes?

Keratocytes = fibroblast-like cells of the corneal stroma; Keratinocytes = keratin-secreting cells of the epidermis

What is the Limbus of the eye?

Transitional area containing epithelial stem cells

What is the histological nature of the Conjunctiva?

Stratified continuation of surface epithelium

What is the function of the Trabecular Meshwork in the limbus?

Channels that drain aqueous humor into the canal of Schlemm

What is the Iris, and what are its two layers?

Most anterior portion of uvea; Anterior layer = dense layer of fibroblasts and melanocytes; Posterior surface = dilator and sphincter pupillae muscles

What is the function and structure of the Ciliary Body?

Encircles the lens; Ciliary muscle = changes lens shape; Ciliary processes = radial ridges covered in ciliary epithelium; Ciliary epithelium = secretes aqueous humor; Ciliary zonules = fibers of fibrillin attached to lens

What is the Choroid, and what is its composition?

Posterior two-thirds of the uvea; loose, well-vascularized connective tissue with melanocytes

From which embryonic structure does the Inner Neural Tunic (Retina) develop?

Neural tube ectoderm

What is the structure and function of the Outer Pigmented Layer of the retina?

Simple cuboidal epithelium with melanin granules; absorbs scattered light and forms the blood-retina barrier

What is the structure and anterior boundary of the Inner Neural Layer of the retina?

Stratified with various neurons and photoreceptors; Ora serrata = anterior border of neural structures

What is the Key Feature of the Inner Limiting Membrane of the retina?

Adjacent to the vitreous body; basement membrane covered by expanded processes of Muller cells

What is the Key Feature of the Nerve Fiber Layer of the retina?

Contains ganglionic cell axons, which converge to form the optic nerve

What is the Key Feature of the Ganglionic Layer of the retina?

Contains cell bodies of ganglion cells

What is the Key Feature of the Inner Plexiform Layer of the retina?

Contains fibers and synapses of ganglion cells and bipolar neurons

What is the Key Feature of the Inner Nuclear Layer of the retina?

Contains cell bodies of bipolar neurons

What is the Key Feature of the Outer Plexiform Layer of the retina?

Contains fibers and synapses of bipolar neurons and photoreceptor cells

What is the Key Feature of the Outer Nuclear Layer of the retina?

Contains cell bodies of photoreceptor cells

What is the Key Feature of the Outer Limiting Membrane of the retina?

Series of adherens junctions between photoreceptors cells and Muller cells

What is the Key Feature of the Rod and Cone Layer of the retina?

Where the photoreceptors of rod and cone cells are located

What cell type forms both the Inner and Outer Limiting Membranes of the retina?

Muller cells

In retinal histology, do Plexiform layers or Nuclear layers come first when moving from inner to outer?

Plexiform (or fiber) layers always come before nuclear layers

What is the inner-to-outer cellular order mnemonic ("GBP") for the retina?

Ganglion cells, Bipolar neurons, Photoreceptor cells

What is the structural description and embryological origin of the Lens?

Transparent, avascular, elastic biconvex structure derived from an invagination of the surface ectoderm

What is the composition of the Lens Capsule?

Made of proteoglycans and type IV collagen