visual system

Question 1

what are the two major photoreceptors of the retina?

Answer 1

rods and cones
20:1
cones have higher visual acuity and located within the fovea

Question 2

macula is…

Answer 2

an oval region that surrounds the fovea

Question 3

major components of the visual system are

Answer 3

optic nerve
the optic chiasm
the optic tracts
the lateral geniculate nuclei of the thalamus

(projections also go to the superior colliculus (visual attention and eye movements) and the pretectal area (involved in the pupillary light reflex))

from the LGN optic radiations (white matter tracts) go to the primary visual cortex (occipital lobe)

Question 4

organisation of the optic radiations

Answer 4

inferior (temporal lobe - AKA= Meyers loop)

• carry information from the inferior retina
• which is the superior visual field

superior (parietal lobe)

• carry information of the superior retina
• which is the inferior visual field

Question 5

L visual hemifields (superior and inferior visual fields) of both eyes travel to which lobe of the primary visual cortex

Answer 5

R side

Question 6

Describe the primary visual cortex

Answer 6

• within the occiptal lobe
• cuneus (superior) and lingula (inferior) are separated by the calcarine fissue
• the cuneus (recieves inferior visual field information)
• the lingula (recieves superior visual field information)

Question 7

the cuneus and the lingula are somatoptically organised into three regions

Answer 7

the visual field regions are like a dart board with three rings; 1 being in the centre (and represents the macula) with 2 and 3 surrounding it

the superior visual field is in the lingula

the inferior visual field is in the cuneus

one hemisphere of the occiptal lobe represents one visual hemifield

Question 8

monocular scotoma is

Answer 8

• a retinal lesion

- retinal infarcts, haemorrhage, degeneration or infection

Question 9

monocular visual loss

Answer 9

damage to the entire retina

Question 10

lesions of the optic nerve can cause

Answer 10

monocular visual loss or monocular scotoma

• glaucoma
• optic neuritis
• raised intracranial pressure
• ischeamic optic neuropathy
• optic glima
• other malignancies
• trauma

Question 11

damage to the optic chiasm

Answer 11

causes a bitemporal hemianopia

• pituitary adenoma
• range of other malignancies

Question 12

retrochiasmal lesion

Answer 12

include lesions of the optic tracts, the LGN, optic radiations or visual cortex
- homomymous visual field defect

Question 13

lesions of the optic tracts cause

Answer 13

contralateral homonymous hemianopia

- tumours, infarct, demyelination

Question 14

optic radiation lesions

Answer 14

• temporal lobe
  contralateral superior quadantanopia
• parietal lobe
  contralateral inferior quandrantopia

Question 15

damage to the entire visual cortex or optic radiations causes

Answer 15

a contralateral homonymous hemianopia

Question 16

macular sparing can occur because

Answer 16

• it has a large cortical representation

- it has collateral blood flow from the MCA and PCA

Question 17

draw the visual field pathway

Answer 17

demonstrate that:

partial lesion of the retina
- monocular scotoma
complete lesion of retina/lesion of the optic nerve
- monocular blindness
lesion of the optic chiasm
- bitemporal hemianopia
meyers loop
- contralateral superior quadrantanopia
parietal loop
- contralateral inferior quadrantanopia
entire lesion of optic radiations/visual cortex
- contralateral homonymous hemianopia