Retina Flashcards
(42 cards)
In which layer of the eyeball is the retina found?
Outer
Which structure of the eye is important for central vision?
Macula, which contains fovea
Which factors are fundamental to visual acuity?
Neural factors
Optic factors
What is visual acuity?
Ability to resolve fine detail
How is visual acuity tested?
Recognition of letters on a Snellen or LogMAR chart
VA=D’/D, where D’=test distance and D=distance where each letter subtends 5 min arc
Describe the optical factors that affect visual acuity?
Pupil size (smaller aperture = clearer vision)
Clarity of optical media (eg. cataracts)
Refractive errors (=blur)
What are photopic and scotopic light levels?
Photopic: well lit
Scotopic: low light levels
What is the best visual acuity and photopic vs scotopic light levels?
Photopic: 6/6
Scotopic: 6/60
Which photoreceptors are acting in photopic vs scotopic light levels?
What impact does this have on visual acuity?
Photopic: cones > high visual acuity
Scotopic: rods > low visual acuity
When is visual acuity highest? Why?
When looking straight ahead in photopic light levels
Utilising the fovea, which has the highest density of cones
When is visual acuity best in scotopic light levels? Why?
When looking to the side (slightly off centre)
Higher density of rods just off to the side of the fovea
List the neural cell types found in the retina?
Rods
Cones
Horizontal cells
Bipolar cells
Amacrine cells
Ganglion cells
What are the two synaptic layers of the retina?
Outer plexiform layer
Inner plexiform layer
At which stage in photoreception does light reach the photoreceptors?
Last
Light passes through all retinal layers before hitting photoreceptors
Describe the difference between rods and cones?
Which photoreceptor type is more sensitive: rods or cones?
Rods
What is the broad explanation for why our day vision is much better than our night vision, even though rods are smaller, more numerous and more densely packed than cones?
Connectivity
Describe the wiring of neurons in the retina?
‘Through’ pathway: PRs-BCs-GCs
Lateral interactions: horizontal cells, amacrine cells
What are the first, second and third order neurons in the retina?
First: photoreceptors
Second: bipolar cells
Third: ganglion cells
Where in the retinal pathway is the nerual signal modulated?
Two places: horizontal cells and amacrine cells
Which cell type is located in the inner nuclear layer of the retina?
What is this layer important for?
Bipolar cells (1x rod bipolar cell, 9x cone bipolar cells)
Important for spatial vision and colour vision
Where are bipolar cells found in the retina?
Inner nuclear layer
Describe the different types of bipolar cells?
Defined by how they respond when light falls on the retina
ON BCs: depolarise when light hits retina
OFF BCs: hyperpolarise when light hits retina
Describe the action of horizontal cells in the retina?
Receive input from, and provide output to photoreceptors
Use GABA (inhibitory) > important for lateral inhibition
Hyperpolarise in response to light
