Lecture 1: the basics of vision Flashcards
what is electromagnetic radiation
photons (or waves) traveling through space and carrying energy
what is electromagnetic spectrum
the range of all possible frequencies of electromagnetic radiation
what is electromagnetic radiation characterized by
what is the formula
frequency and wavelength
v= c / lambda
c=speed of light
lambda=wavelenth
v=frequ
energy is proportional to what
frequency
what are the 4 major eye componenets
cornea
iris/pupil
crystallin lens (lens)
retina
what is the refractive power of the cornea
~40D bc of snell’s law
- constant hydration
- transparent
what is the job of the iris/pupil
iris: contracts and dilates
pupil: regulations retinal illumtination
- reducted aberrations
- increases depth and focus
range of pupil diameter 1-8mm
what is the refractive power of the lens? what is its function
~20D refractive power (relaxed)
- necessary for accommodation
- absorbs short wavelenth light
-chnage in power due to acc: 8D
why does the lens change it’s refractive power
to maintain focus as the object distance varies
what happens when the lens accommodates
the ciliary muscle is contracted, the zonular fibers are relaxed, the tension on the lens capsule is less, the lens becomes thicker and therefore increases its power D
how does the lens absorb short wavelength light?
why does it do it?
it comes at a cost, what happens
by producing chromophores
one possible explanation for this absorption is to protect the retina from high-energy, short wavelength light but comes at a cost=>CATARACTS
what is presbyopia
the lens loses its ability to change its refractive power
- eye cannot accommodate as a result
- onset is ~40 years of age
what is a cataract
lens becomes opaque losing its transparency
- as a result, the light reaching the retina is less than normal
- when opacity increases above some point, VA decreases and the lens has to be replaced w/ an artificial intra-ocular lens (IOL)
in catacts, what kind of damage is there? what kind of disorganization of cells
excessive oxidative damage
gross disorganization and disruption of fiber cells
what is the retina the first stage of
information processing
~400micrometers
-several layers
5cm x 5cm
how large is the fovea
1.8mm diameter
how large is the foveal avascular zone
is there vasculature?
- 7mm diamter
- no retinal vasculature
how large is the foveola
what kind of density, what does it contain
what kind of features does it have
0.3mm diamter
highest photoreceptor density (only cones)
thinnest part of retina
only outer retina features
what is macula lutea
what kind of protiens are here
where is max concentration at?
what role
yellow pigment
lutein, zeaxanthin and meso-zeaxanthin
maximum concentration in the fovea
protective role (AMD?)
what is in the inner retina
ILM NFL ganglion cell layer IPL INL
what is the outer retina
OPL ONL OLM inner segemnts outer segments RPE - bruch's
where are the photoreceptors (rods and cones)
ONL
OLM
Inner segments
outer segments
if you keep the object size the same and double viewing dist, what happens to the visual angle
it is halved
if you keep the viewing dist the same and double the obj size then the visual angle is …..
doubled
what happens if for an object of approx 1 degree of visual angle we double the viewing dist
the object occupies now 0.5 of visual angle
what happens if for an object of approx 1 degree we halve the viewing dist
the object occupies now 2 degrees of visual angle
what happens if we double the size of the object at approx 1 degree and double the viewing dist
the object is still 2 degrees of visual angle
light travels from LGN and visual cortex to where
how does the signal travel
photoreceptors
signal travels from photoreceptors to LGN and visual cortex
wehre does disk shedding/disk phagocytosis occur
the outersegments of RPE
for rods and cones respectively: count peak density time response directionality photopigment temporal resolution light sensitivity spatial sensitivity color visoin adaptation
120 mill, 6 mill ~20 degrees, absent from fovea, 0 degrees -slow, fast -no, sensitive to scattered: yes, sens to direct light -rhodopsin, 3 pigments -low 12Hz, high 60 Hz -really high, low -low, high -no, yes -30 to 40 min, 5-8 min
what is photopigment
a pigment that chemically reacts when it absorbs light (photons)
what is the photopigment rods have
-what does it maximally absorb light at
rhodopsin
maximally absorbs light w/ 507 nm
what are the 3 cone types
what do they absorb light at
- s cones: have cyanolabe which maximally absorbs at 426 nm
- m cones: chlorolabe which max absorbs at 530 nm
- l cones have erythrolabe which max absorb at 557nm
after the photons are absorbed by photopigment, what happens to the photoreceptors
hyperpolarize (their membrane potential becomes negative)
-photoreceptors are directly connected w/ their electrical activiety transmited to horizontal cells and bipolar cells
what is the receptive field of a neuron in the visual system
what is the receptive field of a single photoreceptor
the area that influences the neural activity of the cell
ex. receptive field of a single photoreceptor is their outer segment aperture
a cell that is connected to multiple photoreceptors will have a receptive field of what?
rf equal to the sum of the receptive fields of all of the photoreceptors that it is connected to
what are center-surround receptive fields?
they have a center that depolarizes to light and a surround that hyperpolarizes to light
what does the center surround receptive field show
spatial antagonism or lateral inhibition
- a light has the opposite effect in the surround than in the center
- one part of the receptive field wnats to become active while the other part does not
what are the two types of horizontal cells?
where do they receive input from
how do they transmit signal
where do they receive input from
H1: receive input mainly from both L and M cones
H2: receive input mainly from S cones but also from L and M cones
- they don’t transmit any signal vertically only laterally
- receive input from many cones
what kind of surround are rod bipolar cells
no center surround RF (only ON)
what are the 3 diff types of cone bipolar cells
midget bipolar cells
diffuse bipolar cells
s cone bipolar cells
what is the size of midget bipolar cells in the fovea?
where do they receive their input from in their center RF ?
when do they become larger?
what does their RF ceive input from?
they are smaller in the central fovea and receive input in their center RF from a single L or M cone
they become larger in the periphery and receive input from multiple L or M cones in their center RF
their surround RF receives input from both L and M cones
what are the three modern theories the diff rod to bipolar cell interactions
- rod to rod bipolar cell
- rod to cone bipolar cell through gap junctions w/ cones
- rod to cone ON and OFF bipolar cell
how many types of amacine cells are there
how do they transmit their signal
22
transmit signal both vertically (from bipolar to ganglion cells)
and laterally (from bipolar to bipolar)
how many ganglion cell types ar ethere
what are the 3 types of ganglion cells that are 70% of the total GC population
17
- midget: on and off center surround
- parasol: on and off center surround
- small bistratified: on and off
-high density
what photopigment do ipRGCs (intrinsically photosensitive retinal ganglion cells) contain?
-what are they sensitive to
melanopsin
-sensitive at short wavelengths w/ a peak sensitivity at 488nm
what is the significance of ipRGCs and what are complications that arise from them
sig: regulation of circadian rhythms
- reg of pupillary light reflex
complications: sleep disorders
- seasonal affective disorder (winter blues)
what kind of light do midget GCs, parasol GCs, and small-bistratified GCs relate to
midget: red green
parasol: achromatic
small bi: blue yellow
where does the signal from the GCs project to through the nerve fibers and via the optic disc
lateral geniculate nucleus (LGN)
what are the cells and the pathways for
midget gcs
parasol gcs
small-bistratified gcs
midget: parvo cells (P) and parvocellular pathway
parasol: mango cells (M) and magnocellular pathway
small-bi: konia cells (K) and koniocellular pathway
how do the pathways relate to in the LGN
remain segregate and anatomically distinct
what are the 3 pathways considered to be componenets of
paraller retino-cortical processing
what is the first structure where info from the LGN enters the visual cortex
primary visual cortex (V1)
where is the primary visual cortex located
in the occipital lobe approx at the site of the inion
how many layers does (V1) have?
which pathways project to 4C layer?
4Cb?
4Ca?
- 6 layers w/ 1 being the most superfical
- parvo and magnocellular pathway =4C
- parvocellular -4Cb
- magnocellular-4Ca
what did hubel and wiesel propose
that the cortex is organized into ocular dominant columns and orientation selevtive columns
-now, more complex geometries
information from V1 distributes to what other areas in the ____
occipital lobe like V2, V4, IT (inferotemporal, MT/V5)
what are the 2 info pathways formed from the cortex
the ventral processing stream
the dorsal processing stream
what is the ventral processing stream
object identification and recognition
where is the dorsal processing stream
object’s spatial location visual guided behavior
what is psychophysics
a sub discipline of psychology
- internal (to the subject, soul) processes
- the physical world
waht is the fundatmentals to psychophysics
stimuls=>sensory system=> perception and response
P,R=f (stiumuls)
threshold is reciprolly realted to what
sensitivity
what are the psychophysical tests in clnic
VA
confrontational VF
VF
color vision tests
what is the linear scale
what is the logarithmic scale
linear: a line which is divided into equal parts
log: a line which is divided into equal orders of magnitude (scale of #s w/ a fixed ratio expressed as power of 10)
