Visual System

Question 1

What are the 3 layers of the eye

Answer 1

The eye has three layers
 Outermost sclera (tough and continuous with dural sheath of the optic
nerve)
 Uvea (pigmented vascular layer)
• Choroid sitting just deep to sclera
• Ciliary body and iris sitting anteriorly
 Retina (neural layer) from superficial to deep:
• Retinal pigment epithelium (prevents light from ‘bouncing around’ in the eyeball, causing glare)
• Photoreceptor cells
• Bipolar cells (first order neurones receiving input from
photoreceptors). Bipolar cells are connected by horizontal cells which assist with enhancing edges through a process called lateral inhibition
• Ganglion cell layer (receives input from bipolar cells. Axons of ganglion cells form the…
• Nerve fibre layer
• Interestingly, our retina is the ‘wrong way around’, since light has to
pass through the nerve fibre layer and other layers before getting to the photoreceptors. Cephalopods have a much better arrangement…!

Question 2

What is Oct

Answer 2

Optical coherence tomography (OCT) is a specialist technique that can be used to visualise the layers of retina

Question 3

Describe the norml appearance of the fundus

Answer 3

o Examination of the retina by fundoscopy can detect signs of many diseases such as hypertensive retinopathy, diabetic retinopathy and macular degeneration
o The normal appearance of the fundus, with the macula (point of highest acuity) sitting lateral to the optic disc (point of exit of ganglion cell axons). Branches of central retinal artery and vein are visible on the macula. Occlusion of the central retinal artery (a branch of the ophthalmic artery) causes sudden visual loss known as amaurosis fugax

Question 4

Describe the eye as a pinhole camera

Answer 4

The eye is a pinhole camera
 This implies that light from a lateral visual field is detected by the medial retina and that light from an upper visual field is detected by the inferior retina

Question 5

Describe visual fields

Answer 5

These relate to peripheral vision
Each eye has its own set of visual fields
◦These overlap to form our binocular vision
◦Good for depth perception
o The medial retina is referred to as nasal. Light from the temporal field is detected by the medial retina
o The lateral retina is referred to as temporal. Light from the temporal field is detected by the nasal retina

Question 6

What is the visual pathway comprised of

Answer 6

Optic nevre, optic chiasm, optic tracts, optic radiation

Question 7

Desribe the optic chiasm

Answer 7

2. The Optic Chiasm
   ◦Nasal fibres decussate
   ◦Temporal fibres remain ipsilateral

Question 8

Describe the optic tracts

Answer 8

3. The Optic Tracts
   ◦From Optic Chiasm to Lateral Geniculate Nucleus
   ◦Contain temporal fibres from the ipsilateral side
   ◦Contain nasal fibres from the contralateral side

Question 9

Descirbe the optic radiations

Answer 9

4. 4. The Optic Radiations
      ◦From Lateral Geniculate Nucleus to Primary Visual Cortex (occipital lobe)
      ◦Superior Optic Radiations: PARIETAL LOBE
      ◦Continuation of superior quadrant fibres (temporal and nasal)
      ◦“Baum’s loop”
      ◦Inferior Optic Radiations: TEMPORAL LOBE
      ◦Continuation of inferior quadrant fibres (temporal and nasal)
      ◦“Meyer’s loop”

Question 10

What are visual field defects

Answer 10

These are named based on the area of visual loss rather than the site of the lesion
Examples:
◦Monocular blindness
◦Bitemporal hemianopia
◦Homonomous hemianopia

Question 11

What results from a cn ii lesion

Answer 11

MONOCULAR BLINDNESS 
Temporal and nasal fibres on 
the ipsilateral side are 
affected
Therefore the nasal and 
temporal visual fields are lost on
the ipsilateral side

Question 12

Ehat results from an optic chiasm lesion

Answer 12

Bitemporal hemianopia

Nasal fibres on both sides
are affected
Therefore, both temporal
visual fields are lost

Question 13

What results form a optic tract lesion

Answer 13

Homonymous hemianopia

Ipsilateral temporal fibres and 
contralateral nasal fibres are
affected
Therefore, the ipsilateral nasal 
visual field and contralateral 
temporal visual field are lost

Question 14

Describe fields that the radiation’s are responsible for

Answer 14

◦Superior radiations are responsible for our inferior quadrant field of vision
◦Project into the parietal lobe
◦Inferior radiations are responsible for our superior quadrant field of vision
◦Project into the temporal lobe

Question 15

What results from a lesion of right superior optic radiation (p lobe)

Answer 15

Homologous inferiors quadrantanopia

Lesion of right superior optic radiation
(parietal lobe)
Superior temporal fibre on ipsilateral side is 
affected
◦Loss of inferior nasal visual field
Superior nasal fibre on contralateral side is 
affected
◦Loss of inferior temporal visual field

Question 16

What results from lesion of right inferior optic radiation ( t lobe)

Answer 16

Homologous superior quadrantanopia
Inferior temporal fibre on ipsilateral side is
affected
◦Loss of superior nasal visual field
Inferior nasal fibre on contralateral side is
affected
◦Loss of superior temporal visual field

Question 17

What if both superior and inferior radiations are affects

Answer 17

Homonomoous hemianopia 
Both superior and inferior radiations are 
affected??
◦e.g. Stroke
Superior and inferior temporal fibres
◦Ipsilateral
Superior and inferior nasal fibres
◦Contralateral

Question 18

What happens in a stroke affecting the posterior cerebral artery

Answer 18

Occipital lobe has dual blood supply
◦Posterior cerebral artery
◦Middle cerebral artery (occipital pole)

In a stroke affecting the posterior cerebral artery…
◦Most of occipital lobe will be lost
◦However, middle cerebral supplies the occipital pole (represents the macula)
◦Therefore macular function (central vision) will be spared

Question 19

Describe the pupillary light reflex

Answer 19

Ss

Question 20

Describe the accommodation reflex

Answer 20

• Required for near vision
• 3 aspects (3 ‘C’s):
•Convergence (medial rectus)
•Pupillary Constriction (constrictor pupillae)
•Convexity of the lens to increase refractive power (ciliary muscle)
• Cerebral cortex must be involved because it is relating to image
analysis
• Therefore the reflex follows the visual pathway via the lateral geniculate nucleus to the visual cortex