Orbit in Cross Section
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Frontal bone:
- Part of roof of orbit
- Damaged by trauma that also involves eye and orbit
Superior orbital septum:
- Collagenous curtain connecting frontal bone and upper lid tarsus
- Acts as barrier to inflammation spreading backward from eyelid
Superior tarsus:
- Connective tissue plate containing sebaceous glands that provide oily base for tear film
- Gives firmness to the distal portion of upper lid
- Foreign bodies that fly onto surface of eye often find their way into a slight depression on the conjunctival surface of tarsus (“pre-tarsal sulcus”)
- In order to remove these foreign bodies, evert upper lid
Inferior tarsus:
- Collagenous tissue that gives firmness to lower lid
- Site of Meibomian glands, which secrete much of oily layer of tear film
- May rarely be source of cancer of these glands
Inferior orbital septum:
- Curtain of collagenous tissue that separates lid tissues from orbital tissues
- Acts as barrier to infection coming from skin
Frontal lobe:
- Part of brain that lies over orbit
- Often damaged in blunt trauma that also involves orbital roof
Vitreous cavity:
- filled with clear gel called "vitreous humor"
- vitreous humor (usually just called "vitreous") made up of hyaluronic acid, collagen fibers, and dilute salt water solution
- collagen is thickest in peripheral portion called "vitreous cortex"
- vitreous cortex has firm attachments to anterior retina and border of optic disc
- with aging, inflammation, high myopia, or trauma, vitreous degenerates into lakes of water that place stress on its attachments to retina, and…
- vitreous detaches itself from optic disc, leaving floater, and…
- peripheral vitreous cortex detaches from retina, sometimes tearing hole in retina
- if fluid seeps under retinal hole, retina may detach
- retinal detachment must be emergently repaired surgically to preserve vision
Levator palpebrae superioris muscle:
- Controls elevation of upper eyelid
- Nerve supply comes from superior division of third cranial nerve
- Trauma or nerve damage usually causes lid to droop (“ptosis”),
- Scarring of muscle may lead to lid retraction or deformity
- Other common causes of ptosis are myasthenia gravis, Horner syndrome, third cranial nerve palsy, orbital disorders, and aging
- Common cause of lid retraction is Graves disease
Superior rectus muscle:
- One of six extraocular muscles
- One of four rectus muscles
- Elevates eye
- Supplied by superior division of third cranial nerve
- Damage usually leads to impaired supraduction of eye
- Common causes of impaired supraduction are third cranial nerve palsy, myasthenia gravis, and orbital disorders
Orbital fat:
Inferior rectus muscle:
- One of six extraocular muscles
- One of four rectus muscles
- Moves eye downward
- Supplied by inferior division of third cranial nerve
- Damage usually leads to impaired infraduction of eye
- Common causes of impaired infraduction are third cranial nerve palsy, myasthenia gravis, and orbital disorders