Session 4: The Eye

Question 1

What is the function of sensory cells in the retina?

Answer 1

Synapse with bipolar cells which synapse with the axon of ganglia which run off to form the optic nerve

Question 2

What is the function of melanin in the retina?

Answer 2

Prevents increased refraction. Lack of melanin such as albinism results in increased reflection in the eye

Question 3

What is the function of horizontal cells in the retina?

Answer 3

Involved in lateral vison. Prevent receptor near the centre of vision sending off consuming impulses for vision

Question 4

What is the function of the macular in the retina?

Answer 4

• Area of vision in the centre of the optic disc.

- The fovea is found in the macula and is the area of highest concentration of cone cells

Question 5

What is the function of the rods in the retina?

Answer 5

• Rods are involved in black and white vision.

- They are involved in low light vision

Question 6

What is the function of the cones in the retina?

Answer 6

• Cones are for high visual acuity and discerning details.

- Cones are used for central vision and detail

Question 7

What can be seen on fundoscopy?

Answer 7

• Retinopathies
• Vascular occlusions
• Macula
• Optic disc

Question 8

What is the visual pathway of?

Answer 8

• Temporal fibres run ipsilateral
• Nasal fibres decussate at the optic chiasm
• Optic tract runs to the lateral geniculate nucleus
• Optic radiation split into superior and inferior which runs to the primary visual cortex

Question 9

What are the visual field and what is responsible for them?

Answer 9

• Nasal fibres are responsible or our temporal field of vision
• Temporal fibres are responsible for our nasal field of vision
• Lesions at any point in the pathway will correspond to a pattern of visual loss

Question 10

What is the overview of the visual field defects?

Answer 10

• Before the optic chiasm, signs are unilateral and ipsilateral
• At or after the optic chiasm signs are bilateral
• After the optic chiasm signs will be bilateral and contralateral

Question 11

What is monocular blindness?

Answer 11

• Caused by a lesion of the optic nerve (right)
• Optic nerve glioma or retinoblastoma (children)
• Optic sheath meningiomas (middle aged)

Question 12

What is bitemporal hemianopia?

Answer 12

• Tunnel vision
• Lesion at the optic chiasm
• Affect both nasal fibres therefore both temporal fields lost
• Caused by surrounding structures. Pituitary gland and anterior communicating artery for example

Question 13

What is left homonymous hemianopia?

Answer 13

• Lesion of the right optic tract

- Affect the right temporal and left nasal fibres

Question 14

What is right homonymous hemianopia?

Answer 14

• Lesion of the left optic tract

- Affecting left temporal and right nasal fibres

Question 15

What causes left and right homonymous hemianopia?

Answer 15

• Vascular causes are the most common such as a stroke

- Also neoplasia and trauma

Question 16

What is the blood supply of the occipital lobe?

Answer 16

Dual blood supply

• Posterior cerebral artery
• Middle cerebral artery (occipital pole)

Question 17

What is macular sparing?

Answer 17

• Occurs in Posterior cerebral artery stroke
• 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 18

Whats the important of the macular area?

Answer 18

• Responsible for central vision

- Has a large cortical representation

Question 19

What is the light reflex?

Answer 19

• Light stimulates the afferent nerve in the pathway in CN II
• Synapses in pretectal area
• Gives rise to neurones supplying Edinger Westphal nuclei bilaterally
• Both CN III are stimulated to cause direct and consensual pupillary constriction. Travel along Parasympathetic fibres

Question 20

What are the 3 aspects of the accommodation reflex?

Answer 20

• Convergence (medial rectus)
• Pupillary constriction (constrictor pupillae)
• Convexity of the lens to increase refractive power (ciliary muscle)

Question 21

What is the accommodation reflex?

Answer 21

• Near vision
• 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
• Final aspect of the pathway is common with the light reflex via EWN

Question 22

What is internuclear opthalmaplegia?

Answer 22

• Defect in the medial longitudinal fasciculus
• Muscles of the eye cannot communicate with each other as a result
• Disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction
• Can be affected by multiple sclerosis