L11.2 Regions of the head: Te orbit and eye

Question 1

Blow out fracture of the orbit

Answer 1

• From trauma to the eye → Blood trauma pressure → breaks ethmoid and lacrimal bone in the orbit
• Extra-occular muscles gets trapped in the broken bone → develop double vision
• Surgery → replace with titanium plate
  
  • But if have blood trauma again → may have irreversible damage to the eye as no structures are there to give way

Question 2

Supraorbital margin

Answer 2

• Formed by the Frontal bone
• Supraorbital notch → passage of BV and frontal N

Question 3

Infraorbital margin

Answer 3

• Zygomatic bone (LAT)
• Maxilla (MED)

Question 4

Boundaries of the bones in the orbit

Answer 4

• Apex is deep in the head, base is the front
• Roof
  
  • Frontal bone (blue), lesser wing of sphenoid (yellow)
• Floor
  
  • Maxilla (green), Zygomatic (orange), Palatine (Tiny bit of yellow)
• LAT wall
  
  • Zygomatic, Greater wing of the sphenoid
• MED wall
  
  • Maxilla, Lacrimal bone (purple - very thin), Ethmoid (also very thin), Body of sphenoid

Question 5

Fissures and foramina in the orbit

Answer 5

• Optic canal (optic N passes) next to SUP orbital fissure (most through here)
  
  • Located at the apex
  • Formed by lesser and greater wing of sphenoid

Question 6

3 layers of the orbit

Answer 6

• Outer coat
  
  • Cornea & Sclera
  • Tough coat for protection
• Middle layer
  
  • Uvea
  • Function for nutrition
• Inner coat
  
  • Retina
  • Vision

Question 7

Sclera

Answer 7

• White of the eye, forms 5/6 of eyeball
• Maintains shape and attachments of the muscles
• Made up of collagen → laid down series of whirl → extra strength

Question 8

Cornea

Answer 8

• ANT 1/6 eye
• Transparent and is continuous with sclera
• Layers:
  
  • Corneal epithelial layer
  • Stroma underneath → made up of collagen same as the sclera
  • Endothelium
  • Born with certain number
  • Control water balance and thickness of cornea

Question 9

Why is the cornea transparent and the sclera not, despite being made up of the same substance

Answer 9

• Due to the way which collagen is laid down
• Collagen in sclera is of different size and laid down in whirl
• Collagen in cornea is of uniform size, evenly spaced, parallel bundles (lamellae)
  
  • 200-300 lamellae in stroma

Question 10

What happens when different layers of the cornea is damaged

Answer 10

• If epithelium damaged → able to be repaired
• If stroma damaged → scarring occurs (collagen fibrils are disrupted)
• If endothelium damaged → cornea cannot be repaired and transplant is needed

Question 11

What is the ANT chamber angle

Answer 11

• B/w cornea and iris
• Where fluid (aqueous humour) drains out of the eye
  
  • If blocked → disease like glaucoma
• Has a trabecular meshwork
  
  • Drainage region
• Canal schlemm
  
  • Drains to the venous system

Question 12

Uvea

Answer 12

• Ciliary body
• Iris
• Choroid

Question 13

2 key features of the ciliary body

Answer 13

• Ciliary processes and ciliary muscles

Question 14

Ciliary processes

Answer 14

• Formation of aqueous humour (like the CSF)
  
  • Important for maintaining health of interior of eye
• Point which ligaments attach which attaches to the lens

Question 15

Ciliary muscles

Answer 15

• Accommodate and focusing of lens
• Look far = lens thin; close = lens fat
• Relaxation = look far; Contraction = read
  
  • When contracting → ligaments are not under pressure and allows lens to become fat

Question 16

Iris

Answer 16

• Aperture of the eye
• 2 muscles:
  
  • Sphincter pupillae: Constricts pupil: By PNS
  • Dilator pupillae: Dilates pupil: By SNS

Question 17

Choroid

Answer 17

• Has 3 layers of BV and functions as providing the BS
  
  • The small layer → sit beneath retina
  • Providing vascular supply to outer part of retina (particularly the photoreceptors)
  • Also supplies the structures of the front of the eye

Question 18

Retina features

Answer 18

• Fovea
  
  • NO BV located
• Macula
  
  • Crucial for central vision
  • Fovea is within the area of macula
• POS pole
• Ora serrata
  
  • Edge of retina
  • Where retina joins the other structures of the eye (looks like a serrated edge)

Question 19

Specialised region: Fovea

Answer 19

• Fovea
  
  • Best visual ability Anything impinging visual ability is removed (No Rods)
  • ONLY photoreceptors are located here (Cones)
  • Avascular
    
    • Gets nutrients from choroid

Question 20

Specialised region: Optic nerve

Answer 20

• Formed by the axons of ganglion cells as they exit retina → pass info to higher coritcal areas
• Has to traverses sclera and choroid
  
  • 2/3 of sclera fibres run down side of optic N → provides passage of optic N out
  • 1/3 of the sclera fibres continues across optic N = Lamina cribosa

Question 21

Lamina cribrosa

Answer 21

• Network of collagen fibres that go across optic N to form a sieve
• Gives the optic N structure
• Pressure → may damage structure → damage optic N → glaucoma

Question 22

Orbital BS

Answer 22

• All originate from opthalmic A (from internal carotid A)
• Central Retinal A
• Ciliary A

Question 23

Central retinal A

Answer 23

• → pierece optic N → pass down mid optic N and fans out on the surface of the retina

Question 24

Ciliary A

Answer 24

• Long POS → goes around eyeball to the front
  
  • Anastomose with the ANT ciliary A → inflam inside eye → may cause backflow and cause redness in the ANT ciliary A
  • Supplies photoreceptors across retina and ANT structures (i.e. ciliary body and iris)
• Short POS → pierce around optic N into eyeball
  
  • Both POS travel in the choroid
• ANT → Does not pierce the globe → supplies structure in the front

Question 25

Which artery supplies which part of the retina?

Answer 25

• Dual BS to the retina
• Central retinal → inner retina (neurons that are not photoreceptors)
• POS ciliary A → outer retina (photoreceptors)

Question 26

ANT BS of the eye

Answer 26

• Pass fwd along muscles of the eye to the front of the eye
  
  • Conjuctiva, episclera, sclera, limbus
• Branch down to iris and ciliary body