6. Orbit Anatomy Flashcards
What are the boundaries of the orbit - roof, floor, lateral wall, apex, medial wall? What are the connections into and out of the orbit? What sinuses are located near the orbit? What is a blowout fracture and why is it bad?
Roof: Frontal Bone - contains supraorbital notch/foramen for V1 branch to forehead
Floor: Maxilla + Zygomatic bones
Lateral Wall: Zygomatic and Greater Wing of Sphenoid
Apex: Lesser Wing of Sphenoid
Medial Wall: Maxilla (articulates with frontal), Lacrimal, Ethmoid
Connections: Optic Canal through lesser wing sphenoid (optic nerve, opthalmic artery); Superior Orbital Fissure between sphenoid wings (CN 3,4,6, Opthalmic Vein)
Sinuses: Ethmoid sinus medially, Maxillary sinus inferiorly
Blowout fracture: can cause orbital contents to sag into maxillary sinus (blood can also accumulate)
What are the primordia for the different parts of the eye? (Don’t forget blood vessels, surface ectoderm, CN)
What is a coloboma?
Lens Placode - sinks under surface as lens vesicle gets surrounded by optic cup - LENS
Optic Cup - surrounds (not completely) Lens Vesicle - PIGMENTED and VISUAL RETINA
Head Mesenchyme - from neural crest, condenses around optic cup - SCLERA, CORNEA, CHOROID, MENINGES
Hyaloid vessels - proximal hyaloid artery - CENTRAL HYALOID OF RETINA
Surface ectoderm - EYELID SKIN, CONJUNCTIVAL SACS, CONJUNCTIVA, CORNEAL EPITHELIUM
Coloboma: retention of ventral cleft - optic cup does not surround lens enough - “keyhole” pupil
Optic cup = extension of neural tube
Optic nerve CN2: surrounded by meninges and CSF
Dura Mater = continuous with sclera and cornea
Arachnoid/Pia = continuous with choroid
What are the structures of the eye?
Cornea: covered with stratified squamous epithelium (continues with conjunctiva), avascular corneal stroma (dense ct), simple squamous endothelium
Aqueous humor: fluid under cornea from ciliary body and returned to venous system - where cornea/lens get nutrients
Iris: between 2 ciliary bodies on each side
Pupil: hole in middle of iris
Ciliary Body/Muscle: constricts to change lens shape for close up vision
Lens
vitreous humor: gelatinous fluid behind lens
choroid: middle, vascular layer of posterior eye
Sclera: white of eye, covered with conjunctiva
What are the two different chambers of the eye?
Anterior chamber: in front of ciliary bodies/iris - full of aqueous humor
Posterior Chamber: between iris/lens - where aqueous humor is produced (passes through pupil to ant chamber)
Parts of the retina: optic disc, fovea centralis
optic disc - where optic nerve joins (blind spot)
fovea centralis - in macula lutea (yellow spot), area of most acute vision (all cones)
Smooth muscles in the eye
Iris: circular sphincter m. for pupil (constrict)
radial dilator m. (dilate)
Lens: suspensory ligaments anchor it
Ciliary M. = contraction bends lens for close-up vision (relaxed = flat = see far distance)
Describe the flow through the lacrimal apparatus
Lacrimal Gland Conjunctival Sac Lacrimal Papillae with Lacrimal Puncta Lacrimal Canaliculi (x2 per eye) Lacrimal Sac Nasolacrimal Duct Inf. Meatus of nasal cavity
What are the 5 parts of the eyelid?
Levator palpebral superioris: CN3 innervation - raises eyelid
Superior tarsus muscle: raises eyelid = sympathetic stim
Superior tarsal plate: contains tarsal glands, always secreting, causes CHALAZION when obstructed
Ciliary Glands: opens to eyelash, forms STY when infected
Palpebral Conjunctiva: innermost layer of eyelid on eye
What are the extraocular muscles? What is their embryonic origin? What is the action and innervation of each muscle?
Origin: Head somites
Medial Rectus: CN3 - Adduct Pupil
Superior Rectus: CN3 - Elevate Pupil (deep to levator palpebrae superioris)
Inferior Rectus: CN3 - Depress Pupil
Inferior Oblique Muscle: CN3 - Elevate/Abduct Pupil
Superior Oblique Muscle: CN4 - Depress/Abduct Pupil
Lacteral Rectus: CN6 - Abduct Pupil
What muscles are active to do the following: Pupil Elevation Pupil Depression Pupil Adduction Pupil Abduction
How do you go about clinical testing a specific extraocular eye muscle?
Elevation: Superior Rectus, Inferior Oblique
Depression: Inferior Rectus, Superior Oblique
Adduction: Medial Rectus, Superior Rectus, Inferior Rectus (remember eye on a 45 angle)
Abduction: Lateral Rectus, Superior Oblique, Inferior Oblique
Clinical Testing: Isolate muscle by aligning pupil within muscle’s line of pull
What are the signs of Oculomotor nerve dysfx? Abducens Palsy?
CN3 dysfx: ptosis (no levator palpebrae superioris), pupil dilated (no parasymp), pupil in down and out position (only sup oblique and lat rectus active)
Abducens Palsy: inability to abduct pupil, damaged CN6 - most often CN damaged due to longest CN intracranial course and stretched over petrous part of temporal bone
What are the innervations to: General sensory of eye/orbit Extraocular muscles Parasympathetics for Lacrimal Secretion Motor to Orbicularis Oculi for closing eyelid
V1 (gen sensory) - frontal nerve = supraorbital/supratrochlear branches
Lacrimal nerve
Nasocilary nerve - ciliary ganglion (synapse for parasymps to V1 from CN3)
CN6 to lat rectus
CN4 to sup oblique
CN3 to all other extraoc muscles; parasymps to ciliary ganglion to ciliary nerve to ciliary muscle/pupil constrictor
CN7 - pterygopalatine ganglion - Zygomatic branches (V2) - lacrimal gland for parasymp secretions
CN7 - orbicularis oculi for closing eyelid (where lacrimal parasymps come from too)
What are the two main arteries of the orbit? Where do they run? How are they drained?
Most follow trigeminal nerve brances with same name
Opthalmic artery: travels with optic nerve through optic canal
Central Artery of Retina: travels within optic nerve to retina; functionally an end artery
Drains via: opthalmic veins - cavernous sinus - sup/inf petrosal sinuses - start/end sigmoid sinus - int jugular
