Vision Flashcards
Which work at night, cones or rods?
Rods
What is melanoma associated retinopathy?
A rare complication of melanoma
Antibodies produced against ON bipolar cells
What level of vision is considered legal blindness?
6/60
Which work during the day, cones or rods?
Cones
Which muscle dilates the pupils?
Dilator papillae
What happens to optic nerve fibres at the optic chiasm?
Fibres on the nasal aspect of the retina (that receive light from the temporal visual field) cross and head to the contralateral side of the occipital lobe
How are melanopsin cells involved in light sensitivity found in migraines?
They project to the posterior thalamic nucleus which is also where pain signals from the meninges (thought to be cause of migraines) are received
Which neurotransmitter do ganglion cells release?
Glutamate
Where does the optical radiations communicate between?
Lateral geniculate nucleus of the thalamus and visual cortex
Most ganglion cells send afferent information to which brain area?
Lateral geniculate nucleus of the thalamus
What is special about intriniscally photosensitive ganglion cells ipGCs?
They don’t have connection with photoreceptor cells
They have their own photoreceptor protein called melanopsin
Do ON bipolar cells depolarise or hyperpolarise?
Depolarise
At night or in low light, where is vision best?
8 minutes off centre
How many layers does the lateral geniculate nucleus of the thalamus have? What are they called?
6
Parvocellular and Magnocellular
Do OFF bipolar cells hyperpolarise or depolarise?
Hyperpolarise
What type of damage usually results in macula sparring?
Vascular - the cortical area for the macula in most posterior of occipital lobe where there is extra arterial supply
How are melanopsin cells involved in circadian rhythms?
They sense light and project to the suprachiasmatic nucleus which an important driver for circadian rhythms
Why is vision best at the centre?
That is where the fovea is and has the highest density of cones
How do ganglion cells respond to light?
They depolarise
- Increasing their firing of action potentials
Where is the optic chiasm located?
Above the turkish saddle of the body of the sphenoid bone
What do horizontal cells do?
Receive signals from photoreceptors and send inhibitory GABA responses = hyperpolarise
Which layers of the lateral geniculate nucleus do the right eye input onto?
2,3,5
What is visual acuity?
The ability to resolve fine detail
Bitemporal vision loss is due to damage where? What is common causes?
Optic chiasm
Pathology in the pituitary gland and internal carotid
What cells are in the vertical pathway of neuronal transmission and which cells interact horizontally?
Vertical: Photoreceptor > Bipolar cells > Ganglion cells
Horizontal: Horizontal cells and Amacrine cells
Which ganglion cells do motion? And what percentage of the total number do they make up?
M
10%
Which ganglion cells do colour and acuity and what percentage of the total number do they make up?
P
80%
Which is better than average vision 6/12 or 12/6
12/6
If vision is affected on the same side in both fields, where is the lesion?
Behind the chiasm
How does cGMP interact with Na channels?
cGMP keeps Na channels open causing constant depolarisation
How are vision fields arranged topographically on the visual cortex?
Centre of field on the outer region of the cortex
More lateral aspects of the field inputs to the inner aspect of the cortexs
What is the receptor field of a ganglion?
The area that when light is incident on will change it’s membrane potential
What does 6/12 mean?
A person with that vision must be 6m away from something a person with normal vision can see 12m away
How are melanopsin ganglion cells involved in the papillary reflex?
They receive the light > relay the signal to the pretectal nucleus > which sends efferent to the Edinger Westphal > dilation of pupils
Which ganglion cells are very large?
M
Are there more cones or rods?
Rods - 95:5
How do photoreceptors response to light?
Light causes a conformational change in a protein
Rods: rhodopsin
Cones: cone-opsins
What structural feature is exceptional about amacrine cells?
They have no axons
Explain the phototransduction pathway
Light hit the photoreceptor >
Conformational change in protein eg rhodopsin >
Initiation of cascade Rh > transducin > phosphodiesterase > cGMP broken down > Na channels close >
Hyperpolarisation
How many types of bipolar cells do cone cells have?
9
What is the density of rods at the fovea?
0
What are the two types of bipolar cells?
ON and OFF cells
How are signals from surrounding photoreceptors integrated into the central response?
Through horizontal cells that release inhibitory GABA signal
If vision is affected in one eye only, where is the lesion?
Eye or its optic nerve
What signal do amacrine cells release?
Inhibitory
Which of the retinal cells fire action potentials?
Ganglion cells only
How does pupil size effect vision?
The smaller the aperture - the better vision
What level of vision is required to drive?
6/12
The right visual field is view by which hemisphere?
The left
