Deck 1: Gross Anatomy + Orbits

Describe the characteristics of the eyelid.

• thinnest layer of skin

• has no subcutaneous fat

  • eyelids will never get a fatty layer, no matter how fat you get

List the functions of the eyelid.

• Physical protection of the eye (dust, light)

• Lubrication

What are the 3 actions of eyelids?

1. Reflexive — lid closes fast if an object approaches/touches the eye or lashes

2. Voluntary — squeezing the eyes tightly shut or winking

3. Involuntary — routine blink

Label the Landmarks of the Eye In-situ.

List the key features of the eyebrow.

→ Hair-bearing skin that runs parallel to the superior orbital rim (the bony edge around eye socket)

• Projects from the forehead due to a fat pad

  • esp near the middle, pushing the hairs slightly forward over the eye

• Underlying muscles move the eyebrow during facial expressions

What is the role of the stiff hairs that make up our eyebrow?

protect the eye from dust, sweat, and bright light

What is the role of the supraorbital notch?

passageway for the supraorbital nerve and vessels which supply sensation to upper eyelid, forehead & scalp

What is the Palpebral Fissure?

horizontal opening b/w the upper and lower eyelid margins

How do the eyelids move when open and closed?

Open and looking straight ahead:

• Upper eyelid → covers the top 2–3 mm of the cornea

• Lower eyelid → rests just below the corneoscleral junction (limbus)

When closed:

• Upper eyelid → moves down to cover the entire cornea

• Lower eyelid → moves very little b/c it has less muscle movement

Label.

Label the components of the Palpebral Margins

List the key features of the Palpebral Margins.

• Lash line

  • found in superior and inferior margins

• Gray line

• Meibomian gland orifices

• Mucocutaneous junction (i.e., Marx’s line)

  • line where the skin of the eyelid ends & conjunctiva begins

What are the key features of the lash line and the eyelashes on each eyelid?

→ 2 rows of cilia ‘eyelashes’ on each lid

• Superior - longer & curl upward

• Inferior - shorter & curl downward

-Lash Life cycle = 5 to 11 months

Which nerves are responsible for the sensory innervation that triggers reflex eyelid closure?

• Reflex = sensory

  • Upper eyelid = ophthalmic division of the trigeminal nerve (CN V1)

  • Lower eyelid = maxillary division of the trigeminal nerve (CN V3)

What are the palpebral sulci? How do the superior and inferior palpebral sulci differ?

→ are furrows or creases that appear in the eyelids when the eyes are open

• Superior - forms a distinct upper eyelid crease with a fold

• Inferior - forms a less prominent crease with no fold

What are the palpebral commissures? How do the medial and lateral palpebral commissures differ?

→ junctions where the upper and lower eyelids meet

• Medial - at the inner corner of the eye

• Lateral - at the outer corner of the eye

What do both medial and lateral palpebral commissures define?

Canthi — aka the medial and lateral angles of the eye

What are the major structures of the upper eyelid from anterior to posterior in cross section?

1. Skin

2. Orbicularis oculi muscle

3. Orbital septum

4. Levator Aponeurosis

5. Tarsal plate + sebaceous glands (of Zeis/Meibomian)

6. Müller’s muscle (superior tarsal muscle)

7. Palpebral conjunctiva + its accessory lacrimal glands of Krause and Wolfring

What is the conjunctiva? What is it made up of?

→ entire mucous membrane that lines the inside of the eyelids and covers part of the eyeball

• Bulbar conjunctiva: begins at the limbus (1) and loosely covers the anterior 1/3 of the sclera (visible)

  • Note: remaining 2/3 of the sclera is under the eyelids and is still the bulbar conjunctiva

• Palpebral conjunctiva: pinkish tissue (4) tightly lining the inner surface of the lower eyelid, continuous with eyelids

What happens to the bulbar conjunctiva during massive allergic reactions?

it can billow out beyond the margins of the eyelids

• Recall: it’s loosely attached to the sclera

What is the Conjunctival fornix? What’s another name for it?

→ fold or “blind pocket” created where the bulbar conjunctiva reflects onto the palpebral conjunctiva (3)

• aka “cul-de-sac”

Label the sagittal view of the eyeball.

What are the key features and functions of the eyeball?

Role: focuses light onto photosensitive cells that convert photons → neural signals for visual processing

• has the optical apparatus of the visual system

• occupies most of the anterior portion of the orbit

• 25 mm in diameter

• all anatomical structures within the eyeball have a circular or spherical arrangement

• suspended by 6 EOMS

Describe the anterior and posterior poles of the eye.

Anterior pole = apex of cornea

Posterior pole = the point on the posterior sclera transected by a line normal to the corneal apex at the horizontal equator of the eye

• Note: doesn’t correspond to the position of the optic nerve

Why is the temporal side of the eye is longer than the nasal side?

b/c the optic nerve doesn’t exit exactly at the back center of the eyeball

• exits slightly toward the nasal side

What are the average dimensions of the human eyeball and its clinical range?

• Vertical diameter (height): 23.2 mm (average)

• Horizontal diameter: 24.0 mm (average)

• Antero-posterior (axial) length: 24.3 mm avg

  • Range: 22 mm (very hyperopic) – 27 mm (very myopic)

• Note: Can be measured clinically

What are the key anterior external landmarks of the eye?

• Limbus

• Iris

• Pupil

• When eye is removed: EOM attachments are visible

What is the limbus? What it’s significance in the eye?

→ junction b/w clear cornea & white sclera

• has corneal stem cells

  • Limbal pigment (melanocytes) protects these continuously dividing cells

• Genetic/ancestral adaptation — People from high-sun areas often have a pigmented ring at the limbus

  • due to increased melanocyte production in response to high UV

List the key posterior landmarks of the eye.

**Not visible in-situ

1. Optic nerve

2. Dura mater blends with sclera

3. 4 vortex veins (1 vein/quadrant)

4. IO muscle attachment site

5. LPCA (medial to optic nerve)

6. SPCA

   

What is the order and distance of rectus muscle insertions from the limbus farthest to closest? What’s this anatomical arrangement known as?

Superior = 7.7mm

Lateral = 6.9mm

Inferior = 6.5mm

Medial = 5.5mm

→ This anatomical arrangement = Spiral of Tillaux

List the 3 compartments the eye in made up of. 

What liquid is found in each compartment?

1. Anterior chamber

2. Posterior chamber

3. Vitreous chamber

Aq humour in anterior & posterior 

Vitreous humour in vitreous chamber

Where is the Anterior chamber located?

→ found b/w the cornea & iris and pupil/lens

• contains the anterior chamber angle at its lateral edges

What is the anterior chamber angle?

→ allows for aq humour drainage

• contains TM, Schlemm canal

What is the aqueous humour?

→ clear, nutritive fluid

Function: Meets the metabolic needs of the avascular tissues bordering the anterior chamber, including:

• Cornea

• Lens

• TM

What is the Posterior chamber?

• Donut-shaped space

• Surrounds the crystalline lens

• found b/w the posterior surface of the iris and the inner surface of the ciliary body

What is the Vitreous Chamber?

→ Largest of the spaces within the eye

• Found posterior to the lens

• contains the vitreous body (which is made up of vitreous humour)

What is the vitreous humour?

→ gel-like substance that:

• is 99% water by weight

• has a sparse collagenous support matrix and envelope

Functions:

• Transmits light

• Holds the retina in place

• Supports the lens

  

List the 3 structural layers of the eye and what it contains. (Hint: Mention if these’s structures are found anterior or posterior)

1) Fibrous layer (outer coat/tunic)

• Cornea (anterior)

• Sclera (posterior)

2) Vascular layer (middle coat/tunic)

• Ciliary body (anterior)

• Iris (anterior)

• Choroid (posterior)

3) Inner layer (inner coat/tunic)

• Retina - includes the optic & nonvisual part

❌ What’s Not Included: CT layers that surround the eyeball (bulbar conjunctiva; tenon capsule)

Describe the Fibrous Tunic (outer eyeball layer).

→ AKA “Corneo-Scleral Coat”

• “External fibrous skeleton” of the eyeball

• provides shape and resistance

• provides attachment site for EOMs & intrinsic muscles

Fibrous Tunic

What is the Cornea?

• Transparent

• avascular

• covered by tear film (Thickness: ~0.5 mm)

• Principal refractive surface of the eye

Fibrous Tunic

What is the Sclera?

• Opaque

• fibrous exoskeleton of the eye to which EOMs are attached to

Fibrous Tunic

What are the structures overlying the sclera?

1. Episclera - thin layer of vascularized CT covers the sclera, extending from the limbus all the way to the back of the optic nerve sheath

2. Conjunctiva

Describe the Vascular Tunic (middle eyeball layer).

→ aka the “Uvea”

• Divided into the anterior & posterior uvea

Vascular Tunic

Where do the anterior and posterior uvea meet?

Ora serrata

• b/w ciliary body (end of anterior uvea) & choroid (start of posterior uvea)

Vascular Tunic

What is the Iris?

→ Thin contractile diaphragm with a central aperture- the pupil

• on the anterior surface of the lens

• Function: controls light entry

Vascular Tunic

What is the ciliary body?

→ ring-like thickening of the vascular layer

• found behind the corneoscleral junction

• is muscular & vascular

- Divided into 2 parts:

1. Pars plicata (3) - rough

2. Pars plana (2) - smooth

   

Vascular Tunic

What is the junction b/w the pars plana & retina?

Ora serrata

Recall: Ciliary body is part of the uvea. Ora serrata lies at the transition from the ciliary body (end of anterior) to the choroid (start of posterior uvea)

What is the Ora Serrata?

→ visible line of separation b/w the retina and the irregular posterior border of the ciliary body

• marks the transition from the neural retina (visual) & RPE (non-visual)

What are Crystalline Lens?

• Transparent, biconvex structure enclosed in a capsule

• Location: Posterior to the iris & anterior to the vitreous humor of the vitreous body

• Continues growing throughout adult life → potentially impacts the iris and outflow angle for humor

What structures suspend the crystalline lens, and where do they originate?

→ Zonules are anchoring fibrils that:

• Originate from the ciliary body

• Suspend the crystalline lens in place, behind the pupil

- AKA: “zonular fibers” or “suspensory ligaments”

Vascular layer

What is the Choroid?

→ densely vascularized layer that provides metabolic support for the outer half of the retina

• Highly pigmented! — Dark reddish-brown layer b/w the sclera and retina

  • attached firmly to the pigment layer of the retina but can easily be stripped from the sclera

• is continuous anteriorly with the ciliary body

Describe the Neural Tunic (retina/inner eyeball layer).

→ acts as the sensory neural layer of the eye

- Made of 2 parts:

1. Neural (sensory) retina - “thick visual part”

2. RPE (non-visual) - “thin non-visual part”

💡Think of the retina as a "flattened out nerve" — it’s an extension of the brain

Neural Tunic 

What is the Neural Retina?

→ Photosensitive tissue that converts photons of light into chemical/electrical messages

• originates from the optic nerve which is why it’s the “optic/visual part of retina (functional)”

  

Neural Tunic 

What is the RPE?

Single layer of pigmented epithelial cells that nourish the outer retina

Why is the optic nerve considered a tract of the brain?

→ it’s actually flat piece of the brain (the only part of the brain that’s visible!)

• Surrounded by meningeal coverings (dura, arachnoid, and pia) just like the brain

• contains the CRA & CRV

What is the main artery supplying the eye, and what are its key features?

Ophthalmic artery

• Origin: First branch of the internal carotid artery

• Function: Gives off many smaller branches to provide most of the eye’s blood supply

What are the smaller branches of the Ophthalmic artery group into?

1. Orbital group - supplies external/extracular structures

2. Ocular group - supplies internal ocular structures

List the key branches of the Ophthalmic Artery.

1. CRA: supplies the inner retina

2. Ciliary arteries → LPCA & SPCA

   1. SPCA - supply the choroid & optic nerve head

   2. LPCA - stretch anteriorly to supply the ciliary body & iris 

3. Lacrimal artery: supplies the lacrimal gland, eyelids & conjunctiva

4. Muscular branches: supply the EOMs & send branches to the anterior segment of the eye (anterior ciliary arteries)

The venous blood leaves the eye via four pathways. Outline these pathways. 

1. CRV: drains the retina, running parallel to the CRA

2. Vortex veins: drain the choroid; typically 4-6 veins drain into the superior & inferior ophthalmic veins

3. Superior & inferior ophthalmic veins: main drainage pathways of the eye into the cavernous sinus

4. Anterior ciliary veins: drain the anterior structures (e.g., ciliary body & iris)

What are the characteristics of the cranium/skull?

• made of 22 bones

• has openings and passageways like fissures, foramina, and canals which allow nerves and vessels to enter and exit the cranial vault

List the 7 bones of the orbit.

ELFMPZS

• Ethmoid

• Lacrimal

• Frontal

• Maxilla

• Palatine

• Zygomatic

• Sphenoid

What bones form the orbital rim?

Frontal, Maxillary & Zygomatic bones

• these portions are thicker than the orbital walls

  • BUT 40–60% of all facial fractures still involve the orbital rim

What is the Frontal Sinus?

→ a gap (air-filled cavity) within the frontal bone that makes up one of the paranasal sinuses

What are the components of the orbit?

• Floor

• Roof

• Medial Wall

• Lateral Wall

What is the orbital floor formed from?

• maxilla

• zygomatic

• small contribution from palatine bone

Why is the floor of the orbit commonly damaged in blunt force injuries?

Orbit floor is thicker than medial wall

• BUT it’s often damaged in blunt injuries due to thinning at the infraorbital groove

What is medial wall formed from?

• lesser wing of the sphenoid bone

• lamina papyracea of the ethmoid bone

• lacrimal bone

• maxilla

Along with the orbit floor, why is the medial wall also vulnerable to fractures?

due to the thinness of the translucent lamina papyracea

What is lateral wall formed from?

• greater wing of the sphenoid bone

• zygomatic bone

What is orbital roof formed from?

• lesser wing of the sphenoid bone

• frontal bone

Is the lacrimal fossa the same as the fossa for the lacrimal gland?

❌ No

• Fossa for the lacrimal gland — holds the gland (superolateral orbit)

• Lacrimal fossa — holds the lacrimal sac (inferomedial orbit)

Where is the fossa for the lacrimal gland located? What’s its function?

→ posterior to the superolateral orbital rim, where the inner contour of the frontal bone rises sharply upward

• accommodates/houses the lacrimal gland

Where is the lacrimal fossa located?

→ posterior to the inferomedial rim of the orbit

• accommodates the lacrimal sac

What are the paranasal sinuses and their color codes in diagrams?

Gold -  Frontal sinuses

Pink - Ethmoid sinuses (air cells)

Purple - Maxillary sinuses

Green - Sphenoid sinuses

Which EOMs are strap-shaped and run a direct course from origin to insertion?

• 4 rectus muscles

• inferior oblique

Label.

Label.

Describe the Superior Oblique.

• ovoid shape

• runs anteriorly, parallel to the medial orbital wall and above the medial rectus

• gives rise to a long, slender tendon that runs through the pulley of the trochlea

  

What is the trochlea?

→ cartilaginous loop that’s fixed to the superomedial orbital rim

• after passing through the trochlea, the SO tendon reverses course to insert onto the superior surface of the eye, sliding beneath the SR muscle

What is the annular ring?

• ring that’s attached to the greater and lesser wing of the sphenoid at orbital apex

  • Lesser wing: small, forms roof

  • Greater wing: large, forms floor of middle cranial fossa

• separates the SO fissure into 2 compartments (NASO & LMSFT)

• 4 recti + SO originate here

List the structures inside the ring.

NASO

• nasociliary nerve

• abducens nerve

• sympathetic nerves

• oculomotor nerve

• optic nerve

• ophthalmic artery

List the structures outside the ring.

LMSFT

• lacrimal nerve

• branch of middle meningeal artery

• superior ophthalmic vein

• frontal nerve

• trochlear nerve

What is the Periorbita?

orbital periostium that forms the outer edge of all orbital structures and lines the inside of the orbital bones

What does the fascia surrounding the rectus muscles and levator palpebrae superioris form?

connects the edges of the rectus muscles → form the ‘muscle cone’

What are the 2 principal fascial compartments of the orbit?

1. Intraconal (muscle cone) space – inside the cone of rectus muscles

2. Extraconal space – outside the muscle cone (b/w the periorbita & cone)

What is contained in the intraconal space?

• optic nerve

• ophthalmic artery

• ophthalmic nerves

• permanent orbital fat

What is contained in the extraconal space?

• CT

• vessels

• fat

What is the function of orbital fat?

→ provides cushioning and support for the eye and vasculature

• helping hold the globe forward

Why is orbital fat called “permanent fat”?

→ the only fat that doesn’t get used up under normal conditions

• it can decrease in severe malnutrition, causing the eye to sink back into the orbit

What do the fascial attachments in the orbit form?

→ form ligament-like structures that attach to the orbital walls (annular ring)

• this helps stabilize & control eye movement

What is the function of the fascia that attach to orbital walls (e.g., orbital ligaments)?

1. Controls how strongly the EOMs pull on the eyeball → limits eye movement beyond the orbital aperture/eye socket

2. Hold the globe centered in the orbit

What are the fascial connections in the orbit called?

ligaments

List the principle ligaments.

(1) Lateral Check ligaments

(2) Medial Check ligaments

(3) Ligament of Lockwood

(4) Whitnall’s ligament

List the openings of the orbit.

1. Optic canal

2. Superior orbital fissure

3. Inferior orbital fissure

Note: Very little goes in through the front opening

Supply to the Orbit

Which arterial systems & arteries contribute to the orbital blood supply?

1. Internal carotid system (via the ophthalmic artery)

2. External carotid system (via the infraorbital artery)

Supply to the Orbit

What is the origin of the Ophthalmic artery?

1st branch of internal carotid artery

Supply to the Orbit

What is the origin of the Infraorbital artery?

Maxillary artery - terminal branch of the external carotid artery, within the pterygopalatine fossa

Drainage of the Orbit

How does venous blood drain from the eye and surrounding structures?

→ Venous blood from the eye, orbit, eyelids, and face drains into the superior or inferior ophthalmic veins

• 2 veins have freely anastomosing (interconnecting) vascular fields, allowing shared drainage pathway