6) Retina and Central Visual Pathways

Question 1

What are the layers of the retina from outside to inside?

Answer 1

Pigmented epithelial layer
Photoreceptor cells
Bipolar neurones
Retinal ganglion cells

Question 2

What is the function of the pigmented epithelial layer?

Answer 2

Anchor for photoreceptor cells

Contain melanin to prevent excessive reflections in the eyeball

Question 3

In which condition is there a lack of melanin in the retina? What symptoms occur?

Answer 3

Albinism - struggle in bright lights

Question 4

What are the functions of the photoreceptor cells?

Answer 4

Rods - low level light and black and white

Cones - higher acuity and colour vision

Question 5

What are the functions of the horizontal cells?

Answer 5

Inhibitory interneurones, help to increase contrast by lateral inhibition

Question 6

Describe the fovea centralis:

Answer 6

Depression in macula lutea and has highest density of cones to give high resolution, central vision

Question 7

What clinical features can be seen on fundoscopy?

Answer 7

Retinopathies, vascular occlusions, macula and optic disc (swelling)

Question 8

What is amaurosis fugax?

Answer 8

TIA blocking ophthalmic artery
Curtain over vision due to hypoxia of retina
Prelude to stroke

Question 9

What is OCT?

Answer 9

Optical coherence tomography - high resolution images of retina

Question 10

What is retinal detachment? What symptoms can occur?

Answer 10

When photoreceptors come away from retinal pigment epithelium
Blurring, loss of vision, seeing stars

Question 11

Describe the general visual pathway:

Answer 11

Optic nerve -> optic tract -> optic radiations -> primary visual cortex

Question 12

Describe how the path of temporal and nasal fibres differ:

Answer 12

Temporal fibres run ipsilateral

Nasal fibres decussate at optic chiasm

Question 13

Describe where the optic radiations are located:

Answer 13

Superior in parietal lobe

Inferior in temporal lobe

Question 14

What fibres are responsible for our lateral field of vision?

Answer 14

Nasal

Question 15

What fibres are responsible for our medial field of vision?

Answer 15

Temporal

Question 16

Describe the general features of the signs of a lesion before the optic chiasm:

Answer 16

Signs are unilateral and ipsilateral

Question 17

Describe the general features of the signs of a lesion at the optic chiasm:

Answer 17

Signs are bilateral

Question 18

Describe the general features of the signs of a lesion after the optic chiasm:

Answer 18

Signs are bilateral and contralateral

Question 19

Where would a lesion causing monocular blindness be located?

Answer 19

Optic nerve

Question 20

What are some examples of causes of monocular blindness?

Answer 20

Optic nerve glioma, retinoblastoma (child), optic sheath meningioma (middle aged)

Question 21

Where would a lesion causing bitemporal hemianopia be located?

Answer 21

Optic chiasm

Question 22

What are some examples of causes of bitemporal hemianopia?

Answer 22

Pituitary adenoma

Anterior communicating artery aneurysm

Question 23

Where would a lesion causing left homonymous hemianopia be located?

Answer 23

Right optic tract - affecting right temporal and left nasal fibres

Question 24

What are some examples of causes of left homonymous hemianopia?

Answer 24

Vascular (strokes), neoplasia, trauma

Question 25

What visual field defect would a lesion to the right inferior radiation cause?

Answer 25

Contralateral upper quadrantic anopsia

Question 26

Why can there be macular sparing in a stroke affecting the posterior cerebral artery?

Answer 26

Occipital lobe has dual blood supply from posterior and middle cerebral arteries (occipital pole). Occipital pole is where macula is so central vision spared

Question 27

Describe the pathway for the pupillary light reflex:

Answer 27

Light stimulates afferent (CN II) -> synapses in pretectal area -> gives rise to neurones supplying Edinger-Westphal nucleus bilaterally -> both CN III stimulated to cause direct and consensual pupillary constriction via parasympathetic fibres

Question 28

What are the 3 aspects of the accommodation reflex?

Answer 28

Convergence (medial rectus) Pupillary constriction (constrictor pupillae) Convexity of lens (ciliary muscle)

Question 29

Describe the accommodation reflex pathway:

Answer 29

Follows visual pathway via lateral geniculate nucleus to visual cortex. Fibres from visual cortex to EW nucleus and sphincter pupillae and ciliary muscle. Stimulation of oculomotor nucleus to cause medial rectus contraction

Question 30

What is the function of the medial longitudinal fasciculus?

Answer 30

Controlling movements of the eyes and making sure eyes compensate for movements of the head

Question 31

What structures are connected by the medial longitudinal fasciculus?

Answer 31

Oculomotor, trochlear, abducens and vestibular nuclei