Visual Pathway

Question 1

Name the cells found in the retina

Answer 1

Photoreceptor cells - rods and cone which detect light and send signals to the optic nerve

Horizontal cells - help enhance edges and involved in lateral inhibition

Bipolar cells - primary neurone in visual pathway. Relay signals from photoreceptor cells to the ganglion cells

Ganglion cells - form nerve fibre layer. Axons form the optic nerve

Question 2

What layer in the eye absorbs light, why is this important and which condition does not have this layer

Answer 2

Pigmented layer

Helps stop internal reflection within the eyeball by absorbing protons of light to prevent glare

In albinism, patients have little pigment so have glare

Question 3

Name the parts of the visual pathway

Answer 3

Optic nerve

Optic chiasm

Optic tracts

Lateral geniculate nucleus - part of the thalamus

Superior and inferior optic radiations

Question 4

Where do the radiations run through and which part of the visual field does each radiation supply

Answer 4

Superior radiation - runs through parietal lobe. Supplies inferior visual field

Inferior radiation - runs through temporal lobe. Supplies superior visual field

Question 5

Which neurones decussate at the optic chiasm

Answer 5

Nasal neurones decussate at the optic chiasm while temporal neurones do not

Question 6

Name some forms of visual field defects

Answer 6

Question 7

Describe mononuclear vision loss

Answer 7

Damage to optic nerve resulting in no sight in that eye

Question 8

Describe bitemporal hemianopia

Answer 8

Chiasmal lesion resulting in loss of temporal field

Classically caused by a pituitary adenoma compressing the optic chiasm

Also called tunnel vision

Question 9

Describe contralateral homonymous hemianopia

Answer 9

Damage to the optic tract so there is loss of the same half of the visual field, e.g. damage to left optic tract results in loss of right field vision

Loss of contralateral temporal field and loss of ipsilateral nasal field

Can also occur if primary visal cortex or optic radiations are damaged

Question 10

Describe contralateral superior quadrantopia

Answer 10

Damage to the inferior radiation resulting in loss of ipsilateral superior termporal field and loss of contralateral superior nasal field vision

Question 11

Describe contralateral inferior quadrantopia

Answer 11

Damage to the superior radiation resulting in loss of ipsilateral inferior temporal field and loss of contralateral inferior nasal field vision

Question 12

Describe contralateral homonymous hemianopia with macular sparing

Answer 12

Occurs where there is loss of both temporal or nasal fields but the macular region is spared

Usually occurs in a vascular lesion to the occipital lobe as the macula region is spared by middle cerebral so there will be macular sparing if stroke affects posterior cerebral artery