Anatomy of Eye, Adnexa & Orbit:
- Shape: Pyramidal shaped
- Dimension: Twice as deep as wide
- Orientation: 45-degree angle between orbits
- Eyeball occupies only the anterior half
- Lots of fat & blood vessels
- Functions of the orbital fat:
- Shock absorber, cushion
- Lubrication, fluid movement →Semiliquid fatty pad allows eyeball to spin
- Protect nerves, vessels
- Last place that fat pads will disappear in body (when fat pads disappear→sunken cheek and eyes)
- Functions of the orbital fat:
- Walls of the orbit (7 elements): not smooth, full of holes and grooves
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- Floor: maxilla, zygomatic, palatine
- Medial (fragile bone, paper thin): ethmoid, lacrimal, frontal
- Roof: frontal, sphenoid
- Lateral: zygomatic, sphenoid
Orbital foramina & Fossae
- Optic canal holds optic nerve and ophthalmic artery
- Superior orbital fissure: CN III, IV, V1, VI, ophthalmic veins
- Ophthalmic veins communicate w/ cavernous sinus and facial vein
- Inferior orbital fissure: CN V2 from foramen rotundum
- Both orbital fissures make V shape lateral to optic canal
- Anterior & posterior ethmoidal formina: Anterior & posterior AV & nerves pass through these foramina on the medial wall
- Fossa for lacrimal sac of the superior wall
- Fossa for nasolacrimal canal (inferomedial)
- Canal contains duct→lacrimal fluid from surface of eye into nasal cavity
- Communication between orbit and nasal cavities
Lacrimal gland
- Superolateral part of orbit
- Sensory: V1
- Secretary motor: pteryogoid ganglion of facial nerve
- Produces tears: blinking of eyes causes movement to keep eyes moist
- Brings fluid from lateral corner to medial corner
- Drainage of tears: lacrimal gland→canals→conjunctival sac on surface of eyeball→surface of eye→lacrimal papillae with puncta (holes)→canaliculae→lacrimal sac→nasolacrimal duct
- Conjunctiva: mucosa that covers eyelid and goes onto sclera of eye
- Rich with blood vessels
- Gets inflamed during drinking and when particles touch it
- Conjunctiva: mucosa that covers eyelid and goes onto sclera of eye
- Nasolacrimal duct becomes saturated→crying→nose runs when cry
Eyelids: Protective skin flaps
- Tarsus (superior and inferior): of dense connective tissue plates
- Tarsus contains tarsal glands (mybomium glands)
- Glands open up on inner surface of eyelid
- Glands secrete lubricating liquid to keep eye moist and eyelids from sticking together
- Under hormonal control; sebaceous glands
- Duct can get clogged→get growth
- Ciliary glands associated with eyelashes (cilia): superficial
- Under hormonal control; sebaceous glands
- When clogged→stye
- Muscles
- Levator palpebrae superioris
- Inserts on tarsus superior (dense fibrous band) and goes deep and b/w orbicularis oculi
- Assisted by superior tarsal muscle (sympathetic trunk)
- CN III
- Obicularis oculi
- Forceful and passive closure of eye
- Closing helps moisten cornea and protect from outside particles to prevent inflammation and blindness
- CN VII
- Levator palpebrae superioris
- Common lesions
- Third nerve palsy: affects superior division of oculomotor
- Ptosis: drooping of eyelids
- Mild version: sympathetics to upper eyelid affected
- Bell’s palsy (CN VII)
- Third nerve palsy: affects superior division of oculomotor
Eyeball: Hollow Sphere
- 3 coats
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- Fibrous outer coat
- Sclera: tough, dense fibrous coat that covers 5/6 of eyeball
- Cornea: continuous with sclera, transparent
- Vascular middle coat—three components are continuous
- Choroids: highly vascularzied, most richly vascularized structure in body
- Ciliary body: donut shaped, surrounds lens
- Ciliary zonule of Zinn: radial fibers from ciliary body to lens
- Suspends lens
- Works with zonular fibers—radial (suspensory ligament of lens)
- See more about function in accommodation of lens section below
- Ciliary processes projects from chillier body: produces aqueous humor
- Humor flows from posterior to anterior chamber thru pupil
- Nourishes and bathes cornea and lens (avascular)
- Liquid flows between iriscornea angle→venous channels (sinus venosus sclera, canal of schlemm)
- Channels make circle around perimeter of cornea
- Fluid is replenished every 90 minutes
- Iris: surrounds pupil (hole=aperture of camera)
- Controls amount of light entering by changing shape and size of pupil
- Contraction controlled by inferior division of oculomotor (parasymp)
- Goes thru ciliary ganglion
- Dependent on circular, concentric fibers
- Dilation: Sympathetic control (long ciliary nerves)
- Dependent on radial fibers
- Ciliary zonule of Zinn: radial fibers from ciliary body to lens
- Fibrous outer coat
- Neural inner coat: retina—posterior 5/6
- Retina has two different layers: developed separately
- Pigmented layer: fused with choroids
- Neural layer: picks up light rays
- Axons of ganglion cells travel towards optic disk
- Connect to bipolar cells→rods and cones
- Detached retina: separation of two layers
- Happens to prizefighters
- Continuous with optic nerve at optic disk/papilla:
- In the middle: blind spot with no photoreceptors
- With the optic nerve, find vessels (arteries are branches of ophthalmic artery)
- Travels within dura
- Central artery of retina pierces dura, arachnoid, pia to enter substance of optic nerve
- Macula lutea (lateral to optic disk): yellow spot
- Pit: fovea centralis—only has cones
- Area of acute vision
- Pit: fovea centralis—only has cones
- Retina has two different layers: developed separately