Session 7 - The Eye

Question 1

Draw out the visual pathway from photreceptors to the primary visual cortex

Answer 1

Excellent

Question 2

Give three functional classes of neurone found in the visual system

Answer 2

Photoreceptors - Rods and Cones
Interneurones
Ganglion cells - Bipolar, horziontal and amacrine Magnocellular and Parvocellular

Question 3

What happens at the optic chiasm?

Answer 3

o When action potential reaches the Optic Chiasm, which is situated superior to the Pituitary fossa on the Sphenoid Bone the Nasal Fibres Cross

Question 4

What is contained in the right and left optic tract, respectively?

Answer 4

 R. Optic Tract – Fibres from R. half of each retina, carrying information from L. hemifield
 L. Optic Tract – Fibres from L. half of each retina, carrying information from R. hemifield

Question 5

What do the optic tracts continue to?

Answer 5

the Lateral Geniculate Nucleus of the Thalamus

Question 6

What part of the retina has the largest representation at the lateral geniculate nucleus of the thalamus?

Answer 6

Fovea

Question 7

What lobes do the optic radiations pass through?

Answer 7

Parietal and temporal lobes

Question 8

What fibres loop round the temporal horn of the lateral ventricle, and what is this loop called?

Answer 8

 Fibres corresponding to the inferior half of the retina (Superior visual field) loop around the temporal horn of the lateral ventricle to form Meyer’s Loop

Question 9

Outline the afferent and efferent pathway of the light reflex

Answer 9

Afferent Pathway:
1. Light activates Optic Nerve (CN II) axons
2. Axons (some decussating) pass through the Lateral Geniculate Body
3. Synapse at pretectal nucleus
Efferent Pathway
4. Action potentials pass to Edinger-Westphal nucleus of the Oculomotor Nerve (CN III)
5. Parasympathetic neurones in Oculomotor Nerve (CN III)
6. Innervation of Constrictor Pupillae causes Pupil Constriction

Question 10

What is constriction of the pupil in which the light is shone called, and what is it called when it happens in the other eye as well

Answer 10

The constriction of the pupil that the light is shone into is the Direct Light Reflex. The constriction of the other pupil is the Consensual Light Reflex.

Question 11

What is the corneal reflex?

Answer 11

Also known as the blink reflex, the corneal reflex causes the closure of the eye in response to stimulation of the cornea

Question 12

Give the afferent and efferent pathway of the corneal reflex

Answer 12

Afferent Pathway:
o Action potential is generated when something touches the cornea
o Nasociliary branch of the Ophthalmic Branch of the Trigeminal Nerve (CN V)
Efferent Pathway:
o Temporal and Zygomatic branches of the Facial Nerve (CN VII)
o Causes constriction of orbicularis oculi

Question 13

Give the innervation of the extra-ocular muscles of the orbit

Answer 13

LR6SO4R3
o	Lateral Rectus
	Cranial Nerve 6 
	Abducens
o	Superior Oblique
	Cranial Nerve 4
	Trochlear
o	All the Rest
	Cranial Nerve 3
	Oculomotor

Question 14

What is the vetibulo-ocular reflex?

Answer 14

The vestibulo-ocular reflex is a reflex eye movement that stabilises images on the retina during head movement by producing an eye movement in the direction opposite to head movement.

Question 15

Give the afferent and efferent pathway for the vestibulo-ocular reflex

Answer 15

Afferent Pathway:
o Head movement is detected by the vestibular apparatus of the inner ear, causing firing of action potentials conveyed by the Vestibulocochlear Nerve (CN VIII)
Efferent Pathway:
o Action potentials travel down the nerves innervating Extraocular muscles, causing eye movement in the opposite direction of head movement

Question 16

What would cause an ipsilateral scotoma

Answer 16

 Partial Optic Nerve lesion

 Partial loss of visual acuity, surrounded by good acuity

Question 17

What would cause complete blindness in one eye (2 main overarching causes)

Answer 17

 Ipsilateral Optic Nerve lesion
 Common causes
i. Optic neuritis as a result of MS can cause an ipsilateral optic nerve lesion, as a result of inflammation and destruction of the myelin sheath of the optic nerve.
Other causes include ethambutol and herpes zoster and syphilis
ii. Can also result from Anterior Ischaemic Optic Neuropathy (including diabetes and temporal arteritis)

Question 18

What is a bitemporal hemianopia caused by?

Answer 18

 Optic Chiasm lesion
 Pituitary Adenoma, most often due to lactotrophic adenoma. Often show signs in pregnancy, as progesterone encourages growth of lactotrophs. Treated with bromocriptine.
 Other causes include craniopharyngioma, which is a neoplastic transformation of rathke’s pouch

Question 19

What is a homonoymous hemianopia caused by?

Answer 19

 Optic tract lesion

Question 20

What is homonoymous upper quadrantopia caused by?

Answer 20

 Meyer’s loop lesion

Question 21

What is homonymous hemianopia caused by?

Answer 21

 Optic radiation lesion
 Macular sparing
 Macular sparing occurs due to collateral circulation provided by middle cerebral artery if posterior cerebral is occluded

Question 22

What is horner’s syndrome caused by?

Answer 22

Interruption of a cervical sympathetic trunk results in Horner’s Syndrome. It is manifested by the Absence of Sympathetically Stimulated functions on the Ipsilateral side of the head.

Question 23

What is retinal detachment caused by?

Answer 23

The Intraretinal Space separates the layers of the retina in the developing embryo. During the early foetal period, the layers fuse, obliterating this space. However, although the Pigment Cell Layer becomes firmly fixed to the choroid, its attachment to the Neural Layer is not firm.
Consequently, a blow to the eye may cause detachment of the retina, perhaps days or even weeks after trauma to the eye.

Persons with retinal detachment may complain of flashes of light or specks floating in front of the eye.

Question 24

What is exopthalmos?

Answer 24

Protrusion of the eye, causing the eyelids to part more than normal so that the whites of the sclera are visible all around the cornea and iris.
o	Bilateral
	Grave’s Disease (Hyperthyroidism) 
o	Unilateral
	Aneurysm
	Haematoma

Question 25

What eye symptoms can raised ICP cause?

Answer 25

o Optic nerve is surrounded by meninges with CSF in the subarcachnoid space
o Increase in CSF pressure may compress the optic nerve  compress blood vessels supplying retina  blindness
o Vein is occluded before the artery, leading to oedema of the retina (Papillodema)