Lecture 3 - Eyelids & Conjunctiva

What muscle is the main elevator of the eyebrows and forehead?

Frontalis

What nerve innervates the frontalis muscle?

CN VII (facial nerve)

What muscle acts as the medial depressor of the eyebrow?

Procerus

What nerve innervates the procerus muscle?

CN VII (facial nerve)

What muscle is another medial depressor of the eyebrow?

Corrugator

What nerve innervates the corrugator muscle?

CN VII (facial nerve)

What muscle closes the eyelids and has palpebral and orbital portions?

Orbicularis oculi

What nerve innervates the orbicularis oculi?

CN VII (facial nerve)

What is the muscle of Horner?

A part of the palpebral orbicularis oculi

What structure does the muscle of Horner encircle?

Lacrimal canaliculi

What nerve innervates the muscle of Horner?

CN VII (facial nerve)

What muscle is the main elevator of the upper eyelid?

Superior palpebral levator

What nerve innervates the superior palpebral levator?

CN III (oculomotor nerve)

What is Müller’s muscle (superior tarsal muscle)?

A muscle that provides additional upper lid elevation (~2 mm)

What is the inferior tarsal muscle?

The similar counterpart of Müller’s muscle in the lower lid

What type of innervation does Müller’s muscle receive?

Sympathetic innervation

What is ptosis?

Abnormal positioning or drooping of the upper eyelid

What causes ptosis?

Weakness or paralysis of the levator or Müller’s muscle

How do patients compensate for ptosis?

By using the frontalis muscle

What is Horner’s syndrome?

Disruption of the sympathetic pathway in the head/neck region

Which muscle is affected in Horner’s syndrome?

Müller’s muscle

What is the classic triad of Horner’s syndrome?

Ptosis, miosis, and anhidrosis

What role do eyebrows and eyelids play in communication?

Facial expressions

What protective function do eyelids serve?

Protection of the globe

What reflexive action do eyelids perform regularly?

Blinking and blink reflexes

What nerve provides strong sensory innervation to the eyelashes?

V1

What roles do eyelashes play?

Sensory perception, reflexes, and prevention of environmental debris

Where are the glands responsible for different tear layers located?

In the eyelids

What does blinking stimulate from the meibomian glands?

Lipid release

What does blinking stimulate from the lacrimal and accessory glands?

Aqueous secretion

How do eyelids help distribute tears?

Through lateral to medial eyelid closure

What does tear distribution accomplish?

Spreads tear film across the ocular surface for optics and health

What system is responsible for tear drainage?

Lacrimal pump system

What action does the muscle of Horner perform during tear drainage?

Contracts around puncta and canaliculi, forcing tears into the lacrimal sac

What happens when the orbicularis contracts?

It pulls the lacrimal sac open

What pressure change is created during tear drainage?

Negative pressure

What does negative pressure do in tear drainage?

Draws tears into the lacrimal sac

What happens when the lacrimal sac collapses?

Tears are sent down the nasolacrimal duct

What is a reflex arc?

An involuntary/autonomic response to stimuli

What is the afferent component of a reflex arc?

Transmits information from sensory receptor to nervous system (input)

What is the efferent component of a reflex arc?

Transmits information from nervous system to initiate motor response (output)

What muscular actions cause eyelid closure?

Orbicularis oculi contraction and levator relaxation

What muscle contracts during involuntary eyelid closure?

Palpebral orbicularis oculi

What controls spontaneous blinking?

Subconscious control by the autonomic nervous system

What is the purpose of spontaneous blinking?

Maintain ocular surface optics and health

How often does spontaneous blinking occur?

~12–15 blinks per minute

What triggers reflex blinking?

External sensory stimuli

What is the purpose of reflex blinking?

Protection of the ocular surface

What components are involved in reflex blinking?

Sensory and motor components

Where are all blink reflexes processed?

Brainstem

Which blink reflex does NOT involve cortical input?

Dazzle reflex

How is the dazzle reflex mediated?

By subcortical centers

What triggers the touch blink reflex?

Touch or irritation to cornea or conjunctiva

What is the pathway of the touch blink reflex?

CN V1 → brainstem → CN VII → orbicularis oculi

What is the purpose of the corneal sensitivity test?

To test V1 health

What tools can be used for a corneal sensitivity test?

Cotton swab, dental floss, Cochet-Bonnet

What does a decreased corneal sensitivity response indicate?

Damage to V1

What triggers the auditory blink reflex?

Sudden loud noise

What is the pathway of the auditory blink reflex?

Cochlea → CN VIII → brainstem → CN VII → orbicularis oculi

What triggers the menace blink reflex?

Sudden visual threat or presence of a near object

What is the pathway of the menace blink reflex?

Retina → CN II → visual cortex → brainstem → CN VII → orbicularis oculi

What triggers the dazzle blink reflex?

Sudden bright light

What is the pathway of the dazzle blink reflex?

Retina → CN II → subcortical visual centers (pretectal area) → CN VII → orbicularis oculi

What is blepharospasm?

Involuntary, bilateral, spasmodic contractions of orbicularis oculi

What is another name for blepharospasm?

Benign Essential Blepharospasm (BEB)

What muscles contract during blepharospasm?

Orbicularis oculi, procerus, corrugator

What muscles relax during blepharospasm?

Levator and frontalis

Does benign essential blepharospasm occur due to an external stimulus?

No

What is secondary blepharospasm?

Blepharospasm due to an external stimulus

What are examples of causes of secondary blepharospasm?

Ocular pain or ocular surface irritation

How does voluntary eyelid closure differ from spontaneous blinking?

Increased intensity and duration

What is winking?

Voluntary contraction of palpebral orbicularis oculi

What is the conjunctiva?

A thin, semi-transparent mucous membrane

Where does the conjunctiva extend?

From the limbus over the anterior sclera

What spaces does the conjunctiva create?

Superior and inferior fornices

What surface does the conjunctiva line?

Inner surface of the eyelids

What are the two layers of the conjunctiva?

Stratified non-keratinized epithelium and submucosa

What layers make up the submucosa?

Outer lymphoid layer and deep fibrous layer

What are the divisions of the bulbar conjunctiva?

Scleral and limbal

What are the divisions of the palpebral conjunctiva?

Marginal, tarsal, orbital

What are the divisions of the forniceal conjunctiva?

Superior, inferior, medial, lateral

What protective role does the conjunctiva serve?

Physical protection of underlying tissues and globe

How does conjunctival sensory innervation contribute to protection?

Elicits reflexes

What nerves innervate the bulbar conjunctiva?

Long posterior ciliary nerves

What nerves innervate the superior palpebral conjunctiva?

Frontal and lacrimal nerves

What nerve innervates the inferior palpebral conjunctiva?

Infraorbital nerve

How does the conjunctiva allow movement of the globe and eyelids?

Tissue is loose and flexible, especially in the fornices

Where is conjunctival tissue NOT loose and flexible?

Limbus and EOM insertions

What cells produce mucin proteins in the conjunctiva?

Goblet cells

What type of glands are goblet cells?

Merocrine/apocrine glands

Where is goblet cell density highest?

Conjunctival fornices

What factors influence goblet cell production and secretion?

Autonomic innervation and goblet cell density

What receptors do goblet cells have?

Parasympathetic and sympathetic receptors

What primarily initiates goblet cell secretion?

Parasympathetic stimulation

How does goblet cell density affect secretion?

Fewer cells = decreased secretion; more cells = increased secretion

What causes decreased goblet cells?

Dry eye and autoimmune disease

What causes increased goblet cells?

Allergies, chronic irritation, or injury

What do the conjunctival and corneal epithelium secrete into tears?

Electrolytes and water

How does conjunctival and corneal epithelium secretion affect tear volume?

Contributes separately from goblet cell secretion

What is the net secretion of Cl-/Na+/K+?

Isotonic