The Retina Flashcards
What is visual acuity?
the ability to resolve fine detail
What do the numbers in VA=6/60 mean?
The top number refers to the test distance of 6m, the bottom number refers to what distance a normal person could see it at but the person requires the test distance to see it. A VA of 6/60 is legally blind.
What optical factors affect VA?
pupil size, clarity of optical media, refractive errors
What are the 6 types of neurons in the retina?
rods, cones, horizontal cells, bipolar cells, amacrine cells, ganglion cells
What is the through pathway of the retina?
photoreceptors synapse with bipolar cells which synapse with ganglion cells
What cells are involved in lateral interactions in the retina?
horizontal cells and amacrine cells
What are the different types of bipolar cells and how are they classified?
there are 10 different bipolar cells - 9 are for cones, 1 is for rods - they are also classified according to whether they are on bipolar cells or off bipolar cells
How do on bipolar cells respond to light?
depolarise
How do off bipolar cells respond to light?
hyperpolarise
What type of neurotransmitter do horizontal cells release?
GABA - therefore they are inhibitory
How do horizontal cells respond to light?
they hyperpolarise
What neurotransmitter do amacrine cells release?
GABA and glycine - therefore they are inhibitory
How do on ganglion cells respond to light?
depolarise
How do off ganglion cells respond to light?
hyperpolarise
What neurotransmitter to ganglion cells release?
glutamate
What is the only cell in the retina that fires an action potential?
ganglion cells
What is the receptive field property of a ganglion cell?
centre surround
What happens when light hits a photoreceptor?
light activates rhodopsin which initiates a G protein cascade which activates PDE which breaks down cGMP which closes the cGMP gated sodium channels which hyperpolarises the cell
What type of neurotransmitter do photoreceptors release?
glutamate
What creates the centre surround receptive field property of a ganglion cell?
the through pathway creates the centre and input from horizontal cells determines the surround
What is melanoma associated retinopathy?
a rare complication of melanoma where antibodies are produced and directed against on bipolar cells
