SPECIAL 130 Sudden Visual Disturbance

Question 1

What focuses the light before it reaches the retina?

Answer 1

Cornea and Lens

Question 2

What are the two types of photoreceptors?

Answer 2

Rods and cones

Question 3

What are the cells in the eye that transmit impulses to the CNS?

Answer 3

Ganglion Cells

Question 4

What cells in the eye send excitatory signals to the ganglion cells from the photoreceptors?

Answer 4

Bipolar cells

Question 5

What cells provide lateral inhibition?

Answer 5

Horizontal and amacrine cells

Question 6

Where is there a 1:1:1 ratio of photoreceptors, bipolar and ganglion cells in the eye? What does this result in?

Answer 6

Fovea centralis - increased visual acuity

Question 7

What is the receptive field?

Answer 7

A limited area corresponding with a group of photoreceptors that synapse with a particular ganglion cell

Question 8

Explain ON centred bipolar cells

Answer 8

they increase firing when the centre of the receptive field is stimulated by light
they decrease firing when the peripheral receptive field is stimulated

Question 9

Explain OFF centred bipolar cells

Answer 9

they decrease firing when centre of receptive field is stimulated by light
they increase firing when the peripheral receptive field is stimulated by light

Question 10

What is the state of photoreceptor cells in the dark and why?

Answer 10

They are relatively depolarised (~40mV) as cGMP is raised keeping Na+ channels open

Question 11

What happens to the photoreceptor cells in the light and why?

Answer 11

becomes hyperpolarised due to closing of Na+ channels

Question 12

What happens to 11-cis retinal in response to light?

Answer 12

It becomes all-trans retinal

Question 13

Why does the molecule retinal detach after light exposure?

Answer 13

Rhodopsin cannot bind to retinal in the all-trans state

Question 14

What occurs after retinal detachment in the process of phototransduction in the eye?

Answer 14

Transducin is activated which subsequently activates phosphodiesterate

Question 15

What does phosphodiesterase activation do in the eye?

Answer 15

Converts cGMP to 5’GMP

Question 16

Where do the two optic nerves meet?

Answer 16

Optic chiasm at the base of the skull

Question 17

What optic fibres remain ipsilateral after the optic chiasm?

Answer 17

Fibres from the temporal region of the corresponding eye

Question 18

What optic fibres cross to the contralateral side after the optic chiasm

Answer 18

Fibres from the nasal region of the corresponding eye

Question 19

Where do the optic fibres connect to after the optic chiasm?

Answer 19

Lateral geniculate nucleus, superior colliculus or the pretectal nucleus of the brainstem

Question 20

What and where is the optic radiation?

Answer 20

It is the optic fibres from the lateral geniculate nucleus of the thalamus projecting upward and outwards through the parietal and temporal lobes to the primary visual cortex

Question 21

What is the pupilliary light reflex?

Answer 21

Light stimulus in one eye produces a response in both

Question 22

In the pupilliary light reflex what structures/areas in the brain do the fibres pass to after the optic chiasm?

Answer 22

Pretectal nuclei –> edinger-westphal nucleus (each receives information from both pretectal nuclei) –> oculomotor nerve –>ciliary ganglia –> constrictor muscles of iris

Question 23

What 3 movements can the pupil make in the pupilliary near response?

Answer 23

Convergence, Accommodation and Constriction

Question 24

In the pupilliary near response what pathway does it follow to the visual cortex but what happens after?

Answer 24

Normal sensory pathway. From visual cortex there are projections to the frontal eye field –> EW nuclei –> effector muscles

Question 25

What is the most common cause of blindness/partial sightedness?

Answer 25

Age-related macular degeneration

Question 26

Describe non-exudative, dry AMD

Answer 26

Painless and progressive loss of central vision

Question 27

What degenerative disorder has abnormal neovascularisation in the macula?

Answer 27

Exudate, wet AMD - severe central vision loss

Question 28

What is glaucoma?

Answer 28

Group of diseases where intraocular pressures rises to cause optic nerve damage

Question 29

What is a relative afferent pupilliary defect?

Answer 29

A medical sign observed in the swinging-flashlight test where the pupil has a consensual response but not a direct light response

Question 30

What are the support cells of the eye?

Answer 30

Muller cells

Question 31

What are the 8 histological layers of the eye from surface to deep (humour to choiroid)

Answer 31

``` Inner limiting membrane Nerve fibre layer (ganglia) Inner nuclear layer (synapses) Inner plexiform layer (processor cells e.g. bipolar) Outerplexiform layer (synapses) Photoreceptors Retinal pigment epithelium Choroid ```

Question 32

What is the choroid in the eye?

Answer 32

the vascular supply of the retina

Question 33

What does the retinal pigment epithelium do?

Answer 33

prevents reflection of light and phagocytoses debris