The Visual pathways from retina to visual cortex and eye diseases

Question 1

what do cells in the lateral geniculate nucleus do

Answer 1

• they receive synapses from the retinal ganglion cells and relay this information to the visual or striate cortex
• receives a retinotopic map from the retina to the LGN

Question 2

where does the left lateral geniculate receive information from

Answer 2

• receives information from the right visual field

Question 3

where does the right lateral geniculate receive information from

Answer 3

• receives information from the left visual field

Question 4

desire the layers of the LGN

Answer 4

• there are 6 layers
• each eye projects into an alternate layer
• the ipsilateral eye projects into layers 2,3 and 5
• the contralateral eye projects into layers 1,4 and 6

Question 5

what does the pathway from the retina to the superior collicius do

Answer 5

• the pathway from the retina to the superior colliculus mediate control of involuntary eye movements and this tracks a moving object or fixation of gaze on a fixed object

Question 6

how does the pupillary light reflex work

Answer 6

• information goes in on cranial nerve II the optic nerve and comes out on cranial nerve III the oculomotor nerve
• this is when both eyes are involved in a parasympathetic reflex
• if only the eye illuminated constricts then there is damage to the crossing fibres

Question 7

what are some lesion filed defects

Answer 7

1 Partial optic nerve Ipsilateral scotoma

2 Complete optic nerve Blindness in that eye

3 Optic chiasm Bitemporal hemianopia

4 Optic tract Homonymous hemianopia

5 Meyer’s loop Homonymous upper quadrant anopia

6 Optic radiation Homonymous hemianopia

7 Visual cortex Homonymous hemianopia

8 Macular cortex Central scotomas (bilateral)

Question 8

what is a scotoma

Answer 8

a patch of blindness

Question 9

what do eccentric lesions on the optic nerve produce

Answer 9

• Eccentric lesions of the optic nerve produce scotomas in the nasal or temporal field of the affected eye.
• When a young adult presents with a scotoma, multiple sclerosis must always be suspected

Question 10

what is compression of the middle of the chasm caused by

Answer 10

Compression of the middle of the chiasm is most often caused by an adenoma (benign tumor) of the pituitary gland

Question 11

what happens when lesions of the optic tract occur

Answer 11

• matching visual fields are effected
• outer half which is more exposed are more affected than the inner half and the heminapoia is described as incongruous
• Meyers loop may be selectively caught by a turnout in the temporal lobe

Question 12

what do lesions involving optic radiation include

Answer 12

• include tumors arising in the temporal, parietal, or occipital lobe
• visual fields of both eyes tend to be affected to an equal extent
• Tumors impinging on the radiation from below produce an upper quadrant defect at first whereas tumors impinging from above produce a lower quadrant defect.
• The stem of the radiation occupies the retrolentiform part of the internal capsule and is often compromised for some days by oedema, following hemorrhage from a branch of the middle cerebral artery

Question 13

what does thrombosis of the posterior cerebral artery produce

Answer 13

• produces a homonymous hemianopia

Question 14

what are bilateral central scotomas most often caused by

Answer 14

• caused by a backward fall with occipital concussion

Question 15

what is the most common cause of blindness

Answer 15

• glaucoma

Question 16

what is glaucoma a result of

Answer 16

it is a result of a build up of aqueous humour in the anterior eye chamber due to decreased drainage into the scleral venous sinuses that encircle the anterior chamber

• this causes interocular pressure to rise
• the fluid compresses the lens into the vitreous humour and therefore compresses the retinal neurones and blood supply which cause ischaemia of the eye

Question 17

what does persistent pressure of glucoma result in

Answer 17

= visual impairment form mild to irreversible

Question 18

how is intraocular pressure relieved

Answer 18

• administration of beta adrengeric antagonists that reduce the production of aqueous humour by ciliary processes in the ciliary body

Question 19

what is papillodema

Answer 19

• this is swelling of the optic disc due to an increase in CSF pressure

Question 20

what is papillodema de to

Answer 20

ue to an increase in CSF pressure, raised intracranial pressure, which slows the venous return from the retina by compressing the optic nerve

Question 21

why is papillodema important

Answer 21

It is the most important clinical sign of raised Intra cranial pressure that can be seen during routine neurological examination of the eye,

Question 22

what can an increase in pressure of papillodema also do

Answer 22

• can constrict the retinal ganglion cells axons which can lead to blindness
• as pressure increases the papilla may protrude into the eye, it can also be due to inflammation of the optic nerve head which can cause the papilloedema to be unilateral