The Visual System

Question 1

What are the three layers of the eye?

Answer 1

Outermost sclera

Uvea

Retina

Question 2

Describe the sclera

Answer 2

tough and continuous with dural sheath of the optic nerve

Question 3

Describe the uvea

Answer 3

Pigmented vascular layer.

Choroid sitting just deep to the sclera and the ciliary body and the iris sitting anteriorly.

Question 4

Describe the layers of the retina from superficial to deep.

Answer 4

Retinal pigment epithelium (prevent 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 lateral inhibition.

Ganglion cell layer (receives input form the bipolar cells. Axon of ganglion cells form the…)

Nerve fibres layer

Question 5

What is the macula?

Answer 5

The point of highest acuity.

You can see branches of the central retinal artery and vein here.

Question 6

Where does the macula sit in relation to the optic disc?

Answer 6

Macula is lateral to the optic disc.

Question 7

What is the optic disc?

Answer 7

Point of exit of ganglion cell axons.

Question 8

What is amaurosis fugax?

Answer 8

Occlusion of the central retinal artery (branch of the ophthalmic) causing sudden visual loss.

Question 9

What things can be seen on fundoscopy?

Answer 9

Retinopathies -hypertension, diabetes

Vascular occlusions - brach of central retinal artery or vein

Macula - degeneration

Optic disc - papillodema

Question 10

Describe the pathway of ganglion cell axons to the brain

Answer 10

Ganglion cell axons project to part of the thalamus called the lateral geniculate nucleus via the optic tract.

The lateral geniculate nucleus projects to the visual cortex via the optic radiations.

Question 11

What is the difference between the routes of ganglion which supply the temporal retina and ganglia which supply the nasal retina?

Answer 11

Temporal retina - ipsilateral cerebral hemisphere (no decussation)

Nasal retina - contralateral cerebral hemisphere via optic chasm (decussation occurs).

Question 12

Where do ganglion cells from the superior retina go?

Answer 12

Ganglion cells from the superior retina (inferior field) project through the superior optic radiation running through the parietal lobe.

Question 13

Where do ganglion from the inferior retina go?

Answer 13

Ganglion cells from the inferior retina (superior field) project through the inferior optic radiation running through the parietal lobe.

Question 14

What is a scotoma?

Answer 14

A localised defect in the retina causing a small patch of visual field loss.

Question 15

What causes monocular blindness?

Answer 15

Damage to the optic nerve.

Monocular blindness = can’t see out of one eye

Question 16

What is bitemporal hemianopia and what causes it?

Answer 16

Bitemporal hemianopia = tunnel vision

Caused by damage to the medial chiasm.

Question 17

What is contralateral homonymous hemianopia?

Answer 17

When one side of both the eyes is blind. e.g. can’t see left side of both eyes.

Question 18

What things could cause a contralateral homonymous hemianopia (without macula sparing)?

Answer 18

Damage to lateral geniculate nucleus

Damage to both optic radiations

Question 19

What things could cause a contralateral homonymous hemianopia (wit macula sparing)?

Answer 19

Non-vascular damage to the occipital lobe

Occlusion of the posterior cerebral artery

Question 20

Why do you get macula sparing?

Answer 20

Because the area od the visual cortex that supplies the macula receives blood from the deep branch of the middle cerebral artery as wells the posterior cerebral artery.

Question 21

What visual defect occurs if there is damage to the superior optic radiations?

Answer 21

Damage to the superior optic radiations in the parietal lobe causes contralateral homonymous inferior quadrantanopia

Question 22

What visual defect occurs if there is damage to the inferior optic radiations?

Answer 22

Damage the inferior optic radiation in the temoral lobe causes contralateral homonymous superior quadrantanopia.

Question 23

What is the afferent arm of the pupillary light reflex and accommodation reflex?

Answer 23

Optic nerve

Question 24

What are the processing centres of the pupillary light reflex?

Answer 24

The pretectal nucleus which projects bilaterally to Edinger-Westphal nuclei that contain parasympathetic preganglionics.

Question 25

What is the efferent arm of the pupillary light reflex and the accommodation reflex?

Answer 25

Oculomotor nerve

Question 26

What are the processing centres of the accommodation reflex?

Answer 26

Visual cortex (via lateral geniculate nucleus) allowing processing of visual image which then project to oculomotor and Edinger Wesphal nucleus.

Question 27

What does the accommodation reflex do?

Answer 27

Focusing on a near object leads to pupillary constriction, convergence of themes (contraction of medial recti) and thickening of the lens.

Question 28

What does the pupillary light reflex do?

Answer 28

Illumination of the eye leads to both direct and consensual pupillary constriction. The consensual reflex is mediated by the bilateral projections from the pretectal nucleus.