4) The Retina and Central Visual Pathway

Question 1

What are the two layers the retina ?

Answer 1

> Pigmented Layer

> Neural Layer

Question 2

What is the function of the pigmented layer ?

Answer 2

Retinal pigmented epithelium
> Contains lots of melanin to ensure that there is excessive refraction of light rays.
> The epithelial layer also anchors the photo receptor cells in the neural layer

Question 3

In Albinism, what problems occur ?

Answer 3

Due to the lack of the pigmented layer they are unable prevent excessive refraction of light of rays - Photosenstivity

Question 4

What is the function of the Neural Layer ?

Answer 4

> Contains different types of photoreceptor cells including rods, cones and horizontal cells.

Question 5

What is the function of Horizontal Cells ?

Answer 5

Responsible for lateral inhibition

Question 6

What is the vascular supply of the retina ?

Answer 6

Central Retinal Artery, from the Choroid Layer

Question 7

Outline the Visual Pathway

Answer 7

Optic nerve => Optic Chiasm => Optic Tract => Radiations => Occipital Lobe

Question 8

Outline the pathway that CN II fibres take to the Occipital Lobe

Answer 8

1) Optic Nerve is made up Temporal and Nasal Fibres, Superior and Inferior.

2) At the Optic Chiasm Nasal Fibres Decussate
Where as Temporal Fibres remain Ipsilateral

3) Optic tracts carry fibres to the Lateral Geniculate Nucleis

4) LGN => Primary Visual Cortex
Superior Optic Radiations are continuation of superior T/N fibres => Baum’s Loop (Parietal Lobe)
Inferior Optic Radiations vice versa => Meyer’s Loop (Temporal Lobe)

Question 9

Which fibres are responsible for Temporal Visual Fields ?

Answer 9

Nasal Fibres

Question 10

Which fibres are responsible for Nasal Visual Fields ?

Answer 10

Temporal Fibres

Question 11

Which fibres are responsible for Inferior Visual Fields ?

Answer 11

Superior Fibres

Question 12

Which fibres are responsible for Superior Visual Fields ?

Answer 12

Inferior Fibres

Question 13

What defect will be observed with an Optic Nerve Lesion ?

> Causes

Answer 13

Monocular Blindness 
> Both Temporal and Nasal Fields are gone on affected side.
Causes:
>Retinoblastoma 
> Meningiomas

Question 14

What defect will be observed with an Optic Chiasm Defect

Answer 14

Bitemporal Hemianopia
> Both Nasal Fibres are affected
Causes:
> Pituitary Gland Tumour

Question 15

What defect will be observed with an Optic Tract Defect

Answer 15

Left/Right Homonomous Hemianopia 
> Name depending on where the visual field is lost 
Causes:
> Neoplasia 
> Trauma

Question 16

What defect will be observed with an Optic Radiation Defect ?

Answer 16

Homonomus Qudrantanopias

> Macular Sparing

Question 17

Why is Macular Spared in a stroke affecting Posterior Cerebral Artery ?

Answer 17

Dual blood supply for Occipital Lobe, PCA and Middle Cerebral Artery.
Therefore despite a majority of the Occipital Lobe being lost, Macula is spared

Question 18

Outline the Light Reflex

Answer 18

1) Light enters stimulating CN II
2) II Synapses with EDW in the Pretecal Area
3) P.Sympathetic Response with III
4) Direct and Consensual Pupil Constriction via Constrictor Pupillae

Question 19

Outline the Accommodation Reflex

Answer 19

1) Light Enters Stimulating II
2) Synapses at LGN then goes to Primary Visual Cortex in the Occipital Lobe
3) III efferent nerve synapses at Pretecal Area of EDW to give P.Sympathetic response

Question 20

What 3 things happen in the Accommodation Relfex ?

Answer 20

> Convergence (Medial Rectus)
Pupillary Constriction
Convexity of the Lens to increase refractive power

Question 21

Damage to Medial Longitudinal Fasciculus can lead to what and why ?

Answer 21

Slowed / Absent adduction of ipsilateral eye and Involuntary eye movements

B/c MLF ,a bundle of axons found near the midline of the brainstem, Connects II,IV,VI to prevent diplopia

Question 22

What defect can be seen in a Cerebral Aqueduct Tumour

Answer 22

Compression of EDW and III

Question 23

What is Amaurosis Fugax

Answer 23

Painless temporary loss of vision in one or both eyes caused by blockage of Central Retinal Artery