light and eyes Flashcards
visible light spectrum
400-700 nanometer
blue to red
how light is seen
- absorbed (not transmitted)
- scattered
- reflected
- transmitted (passes through)
- refracted
field of view
the amount of world we are able to see with our eyes.
- we see most with both eyes
- we can control by moving them
Muscles around eye
- medial and lateral rectus muscles: side
- superior and inferior rectus
- inferior and superior oblique
sclera
white of the eye which forms a tough protective coating
cornea
a transparent membrane at the front of the eye
- the first place light eneters
iris
- colored part of the eye that controls how much light enters
- a muscle
- dilates in bright and contracts in dim
pupil
opening in the middle of the iris which control how much light comes in
lens
controls how much of the light is refracted onto retina
- 20% of refraction is done here
ciliary muscles
- muscle that accomodate the lens to make it thicker for close objects and thinner for far away
retina
where the photoreceptors for transduction are
- made of 3 nucleus layers separated by 2 synaptic layers
aquous fluid + cornea
acount for 80% of the focusing of the eye
emmetropia
healthy 20/20 vision
myopia
near focus
- can see close but not far because of an elongation of the eyeball
- image forms in front of retina
Hyperopia
- image forms behind
- can see far but not close
astigmatism
blurred vision at any distance
- usually because of cornea
presbyopia
eyeball becomes less elastic with age and doesnt get as thick, so we can’t see close anymore
Ibn al Haytham
- wrote the book of optics
- thought that light rays come out of the eye
fundus
- the back of the eye
- can be seen with opthalmoscope
photoreceptor cells
- in the outer layer of the retina
- transduce sensory information
- rods and cones
optic disk
- a hole where blood vessels come from
- because of this there are no receptors there so its a blind spot
rods
see dim light
- very sensitive
- 120 million
- more in the peripheral
cones
- less sensitive
- densely packed in fovea
- color and detail
- daylight conditions
- 5 million
types of cones
S-cones: blue
M-cones: green
l-cones: red
- most L and least s
Transduction
photopigments in the rods and cones convert light into neural cones when a photon is absorbed and which cahnges membrane potential and starts an action potential
visual pigment molecules
made up of opsin and retinal
- located inside rods and cones
- when retinal absorbs a photon it changes shape and sets on series of signals (isomeriztion)
retinis pigmentosa
rods are affected which results in night blindness and if it affect cones it would ause full blindness
molecular degeneration
destroys the macula (fovea) which creates a blind spot on the retina
- common with older people
degrees of visual angle
the standard way to measure retinal size.
- function of both its actual size and distance from the observer
dynamic range
our ability to see in bright and dark
factors for dark/light adaptation
pupil dilation and photoreceptor replacement
Photoreceptor replacement
- in light photopigments are used up faster and fewer are there to process more light
- so even though more photons are coming in, that light is thrown away because nothing is there to process it. and we are adapted to that luminance
dark adaptation
- takes longer for us to adapt to dark because rods takes 25 minutes to reach maximum sensitization
- the first 8 minutes cones are mire sensitive and can see better but then they level off
horizontal pathway
made up of horizontal and amacrine cells
horizontal cells
connect perpendicularly to either rods or cones
- they make contact with photoreceptors and bipolar cells
- are responsible for lateral inhibition
amacrine cells
- lateral connection between bipolar and ganglion cells
- help in contrast enhancement and temporal sensitivity
vertical pathway
photoreceptors to bipolar to ganglion
bipolar cells
retinal cells that synapse with on eor more rods or cones and with horizonatal cells and pass signals to ganglion cells
types of bipolar cells
diffuse bipolar cells
midget bipolar cells
diffuse bipolar
receives input from multiple photoreceptors
midget bipolar cell
small cell that receives input from a single cone
- send input to p gnglion in parvocellular pathway
ganglion cells
receive signals from bipolar and amacrine cells and connect into optic nerve
- p ganglion or M ganglion
parvocellular pathway
-aka small cell pathway
midget bipolar to P ganglion to parvocellular
- acuity, color and shape
- good spatial, bad temporal
P ganglion cells
- aka midget ganglion cells
- receive input from midget bipolar cells
M ganglion
receive input from diffuse bipolar cells and connect to the magnocellular pathway
- aka parasol ganglion cells
- motion perception
- aka parasol
magnocellular pathway
receive from diffuse bipolar and connect to magnocellular
- good temporal, bad spatial
- aka large cell pathway
convergence
126 million photoreceptors converge into 1 millionbipolar cells
rod convergence
- about 50 rods to one bipolar cell
- rods are more sensitive because of this convergence, since less light can activate bipolar cells because the input adds up
- however, this makes them worse with detail and acuity
cone convergence
6 cones to each bipolar cell
- in fovea its 1:1
- this ratio helps with acuity
- but less sensitive and needs more light to respond
receptive field
the region on the retina in which stimuli influence a neuron’s firing rate
- each ganglion cell will respond to a specific location on the retina
-M ganglion have larger ones
lateral inhibition
- the horizontal pathway effect the recptive fields on ganglion cells
- makes differences between light and dark even more noticeable (contrast/edges)
on center
excited by light falling on center of ring and inhibited by light on surround
off-center
inhibited by light falling in center of ring and excited by light on surround
mach bands
because of lateral inhibition, the light edges get less inhibition from the dark edge making it look lighter and the dark line gets more inhibition from light edge making it look darker
herman grid
- ## seeing dots at the intersection can be explained by lateral inhibition
visual acuity
smalles spatial detail that our visual system can resolve
- sharpness
- depends on optical factors and sensorineural factors
visual angle
the angle that takes up space in our
spatial frequency
how often a pattern, such as stripes or changes in brightness occur within a given area
filtering out high frequency
- makes image look blurrry
- filtering out low would make us see the edges
fourier analysis
mathematical procedure where signals are separate into components sine waves at different frequencies.
- the visual system breaks down images into a vast number of sine wave gratings with particular frequencies
contrast sensitivity
shows how well we can detect different levels of contrast at different spatial frequencies
- higher contrast is easier to see
