Eyes

Question 1

What bones are likely to be broken in blunt trauma and why?

Answer 1

Lacrimal bone and ethmoid bone - they are both thin, on the medial wall of the orbit

Question 2

What is the sclera? How is the collagen arranged?

Answer 2

Forms 5/6th of the eyeball, is the white part

• maintains the shape of the globe and offers resistance to internal and external forces
• collagen is laid down in whirls

Question 3

What is the cornea?

Answer 3

Anterior 1/6th of the eye, the clear part where light refracts

• made up of layers, epithelium –> endothelium
• is AVASCULAR and TRANSPARENT
• collagen fibrils are laid down in lamellae that are parallel

Question 4

What is the anterior chamber and angle?

Answer 4

Where the cornea, sclera and iris meet

- where the aqueous humour drains out of the eye

Question 5

What are the 3 parts of the ciliary body and what do they do?

Answer 5

Ciliary epithelium - forms the aqueous humour
Ciliary processes - tether the lens
Ciliary muscle - accommodation - focussing

Question 6

What is the ciliary muscle innervated by?

Answer 6

Parasympathetic NS

Question 7

How does focussing work?

Answer 7

Ciliary muscle contracts (sphincter), zonules become relaxed, takes tension off the lens which bulges and becomes fat, enabling lots of light to focus on the retina

Question 8

What is presbyopia?

Answer 8

Loss of accommodation related to age

- caused by reduction in flexibility in the lens capsule and zonules

Question 9

What are the two muscles involved with letting light into the iris?

Answer 9

Sphincter pupillae - constricts the pupil, innervated by the parasympathetic NS
Dilator pupillae - dilates the pupil, innervated by the sympathetic NS

Question 10

What is the significance of the lamina cribrosa?

Answer 10

Part of the sclera that crosses the optic nerve - forms a point of strength of the optic nerve and a sieve like plate –> axons pass through
** if the pressure gets too high then can lose vision due to the bulging of the plate

Question 11

What is the blood supply to the orbit?

Answer 11

Tributaries of the opthalmic artery (which comes off the carotid artery)

• Central Retinal Artery - pierces the optic nerve, fans over the surface of the retina
• Ciliary arteries
• -> posterior ciliary arteries, pierce the globe around the optic nerve, have short and long ones
• -> short feed the choroid, long supply the retina (peripheral vision)
• -> anterior ciliary artery supplies the cornea and anterior structures

Question 12

What is the blood supply to the retina?

Answer 12

Dual blood supply - CRA supplies the inner retina, posterior ciliary artery supplies the outer retina (photoreceptors)

Question 13

What are the muscles of the eyelids and what are their innervations?

Answer 13

Orbicularis oculi - innervated by the 7th CN, closes the eye

Levator palpebrae - innervated by the 3rd CN, opens the eyelid

Question 14

What are saccadic eye movements?

Answer 14

Rapid eye movements that shift fovea rapidly to a new visual target

Question 15

What are the extraocular eye muscles, their movements and innervations?

Answer 15

Superior rectus: elevation (CNIII)
Inferior rectus: depression (CNIII)
Medial rectus: adduction (CNIII)
Lateral rectus: abduction (CNVI)
Superior oblique: torsion, depression when eye adducted (CNIV)
Inferior oblique: torsion, elevates when eye adducted (CNIII)

Question 16

How are the movements from one eye coordinated with those of the other eye?

Answer 16

Via the MLF (medial longitudinal fasiculus)
- pontine paramedian reticular formation is the horizontal gaze centre and coordinates the MR and LR of each eye –> CNIII and CNVI