The Orbit and Eye
Orbit
pear-shaped cavity in the skull that contains the eye, extraocular muscles, optic nerve, lacrimal glands, and eyelids
- made of seven bones: frontal, maxillary, ethmoid, lacrimal, zygomatic, sphenoid, and nasal
- rim is a firm bony ridge: Frontal, zygomatic, maxillary
- supraorbital foramen: transmits the supraorbital nerve (Ό of people have a foramen, Ύs of people have notches)
- SUPERIOR orbital wall
roof, frontal bone, lesser wing of sphenoid
- separates orbit from the anterior cranial fossa and frontal sinus
- MEDIAL orbital wall
lamina papyracea: composed of ethomoid, lacrimal, frontal, sphenoid; is on the side of the
- sinuses; the medial walls are parallel (outer walls are perpendicular)
- ethmoidal foramina- transmits nerve, landmark of brain
- infection can penetrate this paper-thin wall
- INFERIOR orbital wall
floor, maxillary, zygomatic, and palatine bones
- separated from the lateral wall by the inferior orbital fissure, Variable thickness,
- blows to the eye
Þ blow out fractures, orbital tissues get herniated into the maxillary sinuses
LATERAL orbital wall strongest wall, zygomatic and sphenoid
- separated from roof by superior orbital fissure
- OPTIC foramen- contains the optic nerve, ophthalmic artery, etc
Ocular surface anatomy
- 24 mm sphere, covered by lens, variably in the orbit, white due to sclera seen through clear conjunctiva
- Eyelids
protect the eye mechanically and chemically; space between the lids is called the interpalpebral fissure
- skin externally, conjunctiva internally (skin is thinner than normal)
- Orbicularis oculi
(innervated by CN VII) striated circumfrencially around eyelid
- Tarsus connective tissue in eyelid, suspended by canthle tendons (lateral and medial)
- Lacrimal lake, where tears collect
Conjunctiva thin transparent nonkeratizing stratified squamous epithelium; easy to see things through it, because its clear
Muscles eyelids have 4 muscles
Levator
Origin: orbital roof
Insertion: upper eyelid crease CN III
Superior tarsal muscle
Origin: upper side of leavetor
Insertion: on upper tarsal border CN III
6 extraocular muscles 4 recti, 2 obliques
- Origin
: annulus tendon
- Insertion
: on sclera anterior to equatorial plane (Obliques are behind the equator)
- Lateral rectus
CN VI, innervation is always on the inside of the muscle!
- Superior oblique
CN IV, goes through a trochlea, after trochlea all tendon (inferior oblique has minimal tendon) all others innervated by CN III
Muscle Action all muscles except medial and Lateral recti have multiple motions
- intorsion
if 12 oclock goes to the nose
- extorsion
if 12 oclock goes away from the nose
- can use motions to identify muscle weakness: Lateral rectus "look up and out", Inferior oblique "look in and then up"
Orbital Nerves
Ciliary Ganglion a motor root (parasymp.) that synapses in the cilary ganglia then innervates the eyes of the cilia
7th nerve palsy eye more open than normal on affected side.
Optic Nerve CN II, 50 mm long, 1 million fibers
Orbital Vessels
ophthalmic artery most important; veins drain into the cavernous sinus
- Ophthalmic artery
off internal carotid
- Central retinal artery
off ophthalmic artery; runs through the center of the optic nerve; supplies the inner portion of the retina; block will result in blindness
- Anterior ciliary arteries
supplies extraocular arteries
- Veins
have no valves; superior and inferior orbital veins
Lacrimal system
glands make tears; most tears are made in small lacrimal glands all around eyes
- lacrimal gland makes big tears, tears are made and keep eye wet, drain into lacrimal lakes
- sebaceous and mucus contributions to the lacrimal secretions