Muscles around the Eye Flashcards
What are the functions of the eye?
- Self-focus light
- Adjust for light intensity
- Converts light into electrical impulses interpreted by brain
What is the bony orbit?
- Pyramidal bony cavity of facial skeleton
- Lined by periorbita (fascia sheath of the eye)
> continuous at optic canal, superior orbital fissure, inferior orbital fissure, dural fascia
What are the contents of the bony orbit?
- Eyeballs and their extraocular muscles
- Nerves and vessels
- Lacrimal apparatus
Which bones make up the orbital margin?
frontal, maxillary and zygomatic bones
What are the walls of the orbit?
- apex
- 4 walls
- superior
- inferior
- medial
- lateral
What is the superior wall of the orbit formed by?
- orbital part of the frontal bone
– has lacrimal fossa with lacrimal gland - Lesser wing of sphenoid
– near apex
What is the medial wall of the orbit formed by?
- Ethmoid bone (ethmoid plate)
- frontal
- lacrimal
- sphenoid (body)
> Indented by lacrimal fossa for lacrimal sac
> The two walls are separated by ethmoid sinuses and nasal cavity
The inferior wall of the orbit is formed by?
- Maxilla (orbital surface)
- Part of zygomatic and palatine bones
The lateral wall of the orbit is formed by?
- frontal process of zygomatic bone
- Greater wing of sphenoid bone
Describe the location of the apex of the orbit?
- at optical canal
- in lesser wing of sphenoid
- medial to superior orbital fissure
What are the clinical correlations of the orit?
- Fracture of the orbit
- Blowout fracture
> Intraorbital bleeding causing exophthalmos (bulging eyes) - Periorbital Ecchymosis (discoloration of the skin resulting from bleeding underneath)
> Blows to periorbital causes bleeding and swelling - Orbital tumors
> cause exophthalmos
What are the contents of the orbit?
Eyeball
Optic nerve
Ocular muscles
Fascia
Nerves, vessels, fat, lacrimal gland
Conjunctival sac
What are the functions of the yebrows?
- shade
- shield for perspiration
Describe the eyelids?
- skin-covered folds with “tarsal plates” connective tissue inside
- contain tarsal glands that produce an oily substance to prevent eyelids from sticking together
Which muscle opens the eye?
levator palpebrae superioris
- only present in the superior eyelid because it is the only one that opens
Describe the canthus (corner of the eye)?
- Lacrimal caruncle makes eye “sand” at medial corner
- Epicanthal folds in many Asian people cover caruncle
- Tarsal glands make oil to slow drying
Describe eyelashes?
- ciliary gland at hair follicle
- touch sensitive, thus blink
What is the conjuctiva?
Mucous membrane that coats inner surface of eyelid (palpebral part) and then folds back onto surface of eye (ocular part)
Describe the histology of the conjuctiva?
- Thin layer of connective tissue covered with stratified columnar epithelium
- Very thin and transparent, showing blood vessels underneath (blood-shot eyes)
- Goblet cells in epithelium secrete mucous to keep eyes moist
Why is vitamin A necessary in the conjuctiva?
Vitamin A necessary for all epithelial secretions
— lack leads to conjunctiva drying up
> scaly eye
What are tears?
contain mucous, antibodies, lysozyme (anti-bacterial)
What structures produce and transport tears?
- Lacrimal glands
— superficial/lateral in orbit, produce tears - Lacrimal duct (nasolacrimal duct)
— medial corner of eye carries tears to nasal cavity
> frequently closed in new borns — opens by 1 year usually
Describe the flow of tears through the lacrimal apparatus?
Produced by lacrimal gland
> spread over eyeball
> lacrimal lake
> lacrimal canaliculi
> lacrimal sac
> nasolacrimal duct
> inferior nasal meatus
What are the 2 groups of muscles within the orbit?
- Extrinsic muscles of the eyeball
- extra-ocular muscles - Intrinsic muscles of the eyeball
- control the shape of the lens and size of pupil
Name the 3 nerves that innervate the eye muscles?
- Occulomotor
- Abducens
- trochlear
Name the extrinsic eye muscles?
- superior oblique
- lateral rectus
- medial rectus
- superior rectus
- inferior rectus
- inferior oblique
State the movement, innervation and testing of the superior oblique muscle?
movement = depresses eye + medial rotation
innervation = CN IV Trochlear
test = look medially and downward
State the movement, innervation and testing of the lateral rectus muscle?
movement = lateral rotation
innervation = CN VI Abducens
test = look laterally
State the movement, innervation and test of the medial rectus muscle?
movement = medial rotation
innervation = CN III Oculomotor nerve
test = look medially
State the movement, innervation and testing of the superior rectus muscle?
movement = elevates
innervation = CN III Oculomotor nerve
test = look medially and upward
State the movement, innervation and testing of the inferior rectus muscle?
movement = depresses
innervation = CN III Oculomotor
test = look laterally and downward
State the movement, innervation and testing of the inferior oblique muscle?
movement = elevates eye + lateral rotation
innervation = CN III Oculomotor nerve
test = look laterally and upward
What is intorsion?
medial (inward) rotation of upper pole (12 o’clock position) of cornea
> caused by superior oblique and superior rectus
What is extorsion?
Lateral (outward) rotation of superior pole of the cornea
> caused by inferior rectus and inferior oblique
What will happen to the position of the eyes if there is damage to the right abducent nerve - the sixth cranial nerve?
right eye rotates medially
What will happen if there is damage to the trochlear nerve - the fourth cranial nerve?
eye rotates laterally and upward
What will happen if there is damage to the third cranial nerve - the oculomotor nerve?
eye rotates laterally and downward
Name the 3 layers that support and maintain the eye?
- Outer fibrous layer
- Middle vascular (pigmented) layer
- Inner layer
What are the consequences of a lesion of the CN III nerve?
complete ptosis
- drooping of the upper eyelid
State the origin, insertion, innervation and action of the levator palpebrae superioris?
Origin: lesser wing of shpenoid
Insertion: anterior surface of the tarsal
Innervation: Occulomotor nerve (CNIII)
Action: Elevation of upper eyelid
