Lecture 30: Regions of the Head: The Orbit & Eye

Question 1

What is a blowout fracture of the orbit?

Answer 1

Common with blunt trauma to they eye, bones break to relieve pressure blood is putting on eye and fall into maxillary sinus

Question 2

What bones form the supraorbital margin and what is significant about this margin?

Answer 2

Frontal Bone

Supraorbital notch - passage or vessels and nerves to the forehead

Question 3

What bones form the infraorbital margin?

Answer 3

Zygomatic laterally and maxilla medially

Question 4

What are the bones of the orbit (roof, floor, lateral, medial)?

Answer 4

• Roof: frontal bone and lesser wing of sphenoid
• Floor: maxilla (medial), zygomatic (lateral), palatine
• Lateral: zygomatic, greater wing of sphenoid
• Medial: maxilla, lacrimal bones, ethmoid, body of sphenoid (lacrimal and ethmoid very thin)

Question 5

How does double vision happen?

Answer 5

Break orbital bones, fall into maxilla and extra ocular muscles get trapped and cannot move eye in normal way

Question 6

If broken orbital bones are replaced with a titanium plate and trauma happens again what happens?

Answer 6

If trauma is repeated after replacement with titanium plate - no bones to break to reduce pressure on eye from blood (reduce damage) - irreversible damage

Question 7

What are the weakest bones in the orbit?

Answer 7

Lacrimal and ethmoid

Question 8

What is the superior orbital fissure?

Answer 8

Gap between lesser and greater wings of sphenoid where most vessels and nerves to the eyes move through

Question 9

What are the 3 layers of the eye and their functions?

Answer 9

Outer coat: cornea and sclera, function for strength
Middle coat: uvea, formed by a number of different structure (carotid, ciliary body and iris), function is nutrition
Inner coat: retina, nerves for vision

Question 10

What are the features of the sclera?

Answer 10

• 5/6 of the eyeball
• Maintains shape and offers resistance against forces
• Provides attachment for extraocular muscles
• Point of extreme strength and resistance
• Made up of collagen laid down in a muddled way – series of whirls for greatest strength

Question 11

What are the features of the cornea?

Answer 11

• Anterior 1/6 of eyeball
• Refracting component of eye
• Avascular and transparent
• 5 layers

Question 12

What is special about the layers of the cornea?

Answer 12

Epithelium: constantly dividing cells
Stroma: fatty layer, transparent
Endothelium: finite number of cells, damage will require transplant, maintains water balance and thickness of cornea

Question 13

Why is the cornea transparent?

Answer 13

Collagen fibrils are uniform in diameter, evenly spaced and run in parallel to each other (each lamellae)

Question 14

How many lamellae in each stroma?

Answer 14

200-300

Question 15

What happens when there is a scratch on different layers of the cornea?

Answer 15

Epithelium - repair in 7 days
Stroma - scarring due to disruption of collagen fibres
Endothelium - cornea cannot repair, transplant needed

Question 16

What is the anterior chamber?

Answer 16

Area between iris and cornea

Question 17

Where does the aqueous humour drain?

Answer 17

Anterior chamber angle - trabecular meshwork - canal of schlemm - venous system

Question 18

What happens is anterior chamber angle is blocked?

Answer 18

Glaucoma

Question 19

What are the functions of the ciliary body in the uvea?

Answer 19

• Forms aqueous humour
• Tethers lens via ligaments and ciliary processes
• Ciliary muscle for accommodaition

Question 20

What are the components of aqueous humour?

Answer 20

Watery - lots of ions, nutrients and minerals but little protein

Question 21

What is accommodation?

Answer 21

Under normal circumstances the ciliary muscle is relaxed with the lens sitting in the middle - ligaments pulling, lens is thin. When you contract ciliary muscle ligaments are not under tension and so lens gets fat when not under restriction - focus on something close up (accommodation)

Question 22

What are the features of the iris?

Answer 22

• Colour part of eye
• Changes pupil size via muscles
• Sphincter pupillae – constricts pupil, PNS
• Dilator pupillae – dilates pupil, SNS (muscular epithelium)

Question 23

What are the features of the choroid?

Answer 23

• Middle layer of the 3 layers (sclera, choroid, retina)
• 3 layers of blood vessels (big, medium, small) – most important is the choriocapillaris (sits just below the retina)
• Small vessels sit just below the retina
• Blood vessels are crucial for suppling nutrients to the outer retina – photoreceptors

Question 24

What of the optic nerve can you see in the eye?

Answer 24

Optic nerve head

Question 25

What is the macula?

Answer 25

Where no blood vessels are located, important for central vision, most important part is the fovea

Question 26

What is the posterior pole?

Answer 26

Region outside of the macula

Question 27

What is the ora serrata?

Answer 27

Edge of the retina, where the retina joins the other structures of the eyeball, looks like a serrated edge

Question 28

What are the features of the fovea?

Answer 28

High visual acuity, avascular, gets nutrients from choroid, high density of cones (important for daytime), no rods (remove anything that may impinge on the ability to see – only have photoreceptors present here)

Question 29

What forms the optic nerve?

Answer 29

Formed by the axons of ganglion cells as they exit the retina to pass visual info to higher cortical areas (3rd order neurons)

Question 30

How does the sclera move in relation to the optic nerve?

Answer 30

Optic nerve has to move through the layers of the eye – sclera and choroid. 2/3 of sclera fibres do a U-turn and run down the side of the optic nerve – other 1/3 travel across the optic nerve (lamina cribosa – siv)

Question 31

What is the lamina cribosa?

Answer 31

Meshwork of collagen fibres that go across the optic nerve to form a sieve, each hole contains the bundles of nerve fibres that project from the retina to the brain – this gives the retina structure.

Question 32

What happens if the lamina cribosa is bent?

Answer 32

Glaucoma

Question 33

Where does the blood supply for the eye originate and what are the branches?

Answer 33

Internal Carotid Ophthalmic -Central retinal -Ciliary arteries

Question 34

What are the features of the central retinal artery?

Answer 34

Pierces optic nerve, passes down middle and fans over the surface of the retina, supplies inside retinal neurones (not photoreceptors) - 2nd and 3rd order

Question 35

What are the features of the short posterior ciliary arteries?

Answer 35

Supply optic nerve head and photoreceptors closest to the optic nerve

Question 36

What are the features of the long posterior ciliary arteries?

Answer 36

Pierce globe and move to front

Question 37

Where do posterior ciliary arteries travel?

Answer 37

Choroid

Question 38

What are the features of the anterior ciliary arteries?

Answer 38

Anterior ciliary artery doesn’t pierce the globe and travels outside the eyeball to the front and supplies anterior structures (conjunctiva, episclera, sclera and limbus), pass along extraocular muscles

Question 39

What leads to an episceral circle?

Answer 39

Inflammation in the eye - back flow into arteries that anastomose - poster ciliary and anterior ciliary arteries