week 10 (vision) Flashcards
(47 cards)
1
Q
explain: basic qualities of a light wave (3)
A
-
wavelength
- lambda
- prod. diff. colours
- from peak to peak -
freq.
- number of waves
- E = proportional to freq.
⤷ higher E = shorter wavelength = higher freq.
- shorter wavelength = higher freq (vv) -
amplitude
- diff. between baseline and peak/trough
2
Q
question: which colour has the highest energy? shortest wavelength? least E? longest wavelength?
A
- higher E + shorter wavelength = blue/purple
- lower E + longer wavelength = red
3
Q
name + explain: ways light rays can interact w/ things (5)
A
-
reflection
- bouncing off a surface -
absorption
- transfer of light E into a particle/surface -
transmission
- neither reflected or absorbed
⤷ just passing through a medium -
refraction
- bending of rays
⤷ bc speed of light differs in diff. mediums -
scattering
- light = dispersed in irregular fashion
4
Q
explain: retina
A
- has photoreceptors
- light focused here
- lines back of eye
- has fovea
⤷ spot where visual acuity is highest
⤷ a lot of cones
5
Q
explain: optic nerve
A
- bundle of axons from retina
- transmits vis. info to brain
- makes blind spot on retina
6
Q
explain: cornea
A
- continuation of the sclera
- has sensory endings
- refracts light
7
Q
compare: aqueous vs vitreous humor
A
AQUEOUS
- front of eye
- near lens and cornea
VITREOUS
- transparent and refractive
- fills back of eye
BOTH
- keep psi on eye to keep shape
8
Q
name: layers of eye in order from outermost to inner
A
sclera
choroid (blood vessels to nourish retina)
retina
vitreous humor
9
Q
explain: schematic eye
A
- theoretical + simplified model of eye
- main refractive components = cornea and lens
- has retina
10
Q
explain: emmetropic eye
A
- optically normal eye
- explains a perfect eye
- light rays come in from parallel rays
- distance + refractive power = perfectly matched to length of eyeball
11
Q
question: what happens if an object is closer than optical infinity?
A
- lens and cornea don’t have enough refractive power to converge onto retina in a point
⤷ point = behind retina - causes blurry image
- need accommodation of lens
12
Q
define: accommodation
A
- changing lens curvature to respond to changing object distance
- relax musc = ligaments pulled = flatter lens (for further)
- contract closer to lengs = ligaments relax = rounder lens (for closer)
13
Q
question: is a rounder lens better for far or close objects?
A
- round = shorter distance (closer)
⤷ refracts more - flat = further distance
14
Q
define: focal distance
A
- distance from refractive surface and the point where parallel rays converge
15
Q
define: diopter
A
- measure of optical power of a lens
- larger D = stronger lens = bends light more
16
Q
question: does a fat lens have more or less refractive power? diopters?
A
- more refractive power
⤷ power of cornea and lens - higher power
- more diopters
17
Q
question: how does a retinal image differ from the visual scene?
A
- inverted horizontally
- upside down
- more blurry on edges
18
Q
compare: hyperopia vs myopia
A
HYPEROPIA
- far sightedness
- can see far but not close
- focal point is behind retina
- cornea not curved enough or eyeball too short
⤷ lens lacks refractive power
- need convex lens to add refractive power
⤷ bulge out
MYOPIA
- near sightedness
- can see close but not far
- focal point is before retina
- cornea too curved or long eyeball (makes retina further back)
⤷ lens can’t flatten enough
- need concave lenses
⤷ diverges light
19
Q
explain: presbyopia
A
- age related hardening of the lens
- reduction in elasticity of capture that holds lens
- treated w/ convex lenses or bifocals
⤷ bifocals = for ppl w/ existing refractive errors (lens w/ one power on top and another at bottom)
20
Q
explain: astigmatism
A
- lack of symmetry of curvature of cornea
- diff. refractive power along horizontal and vertical axes
⤷ causes blurred retinal image along affected direction only - treat w/ special lenses to correct refractive deficit
21
Q
name: layers of retina in order from outermost to inner
A
retinal pigment epithelium
photoreceptors
inner nuclear layer (bipolar cells)
ganglion cell layer (ganglion cells)
inner limiting membrane
22
Q
explain: RPE
A
- retinal pigment epithelium
- absorbs any extra light not absorbed by photoreceptors
- prevents scattering
- helps regenerate bleached photopigments
23
Q
compare: rods vs cones
A
RODS
- 90 million
- periphery of retina
- no colour
- night vision
CONES
- 4 - 5 million
- center of retina
⤷ fovea
- colour
- day vision
- 3 types
⤷ red (L)
⤷ green (M)
⤷ blue (S)
24
Q
name: structures of a photoreceptor
A
-
outer segment
- top part
- holds photopigment -
inner segment
- makes photopigment - synaptic terminal
- send info
- uses graded potentials bc short distance
**not transmission w/ AP
25
explain: distribution of rods and cones in retina
- cone density = highest in fovea
- rod density = highest in periphery
- no photoreceptors in optic disc (optic nerve)
⤷ blind spot
26
explain: scotopic vision
- dim light conditions
- rods more efficient than cones
- rods = active at low lvls of light
⤷ means no colour + poor acuity
27
explain: mesopic vision
- intermediate lighting (ex. moonlight)
- passing cone threshold
- both rods and cones activated
- at certain point -> rod saturation begins
⤷ photopigment can't be activated anymore -> bleaching
28
explain: photopic vision
- brighter conditions (indoor lighting + higher)
- only cones
- cones have mech. to prevent bleaching at high light
- good colour vision best acuity
29
question: what happens to bleached photopigments?
- need to be regenerated
- regen. by RPE
- reconverts pig shape to be able to absorb light again
30
name: ways vis. system adjusts to changes in illumination (4)
1. rods and cones have diff. ranges -> can change vision type
2. photopigment must be regenerated
3. pupil can be adjusted
4. ganglion cells resp. best to contrast light (no diffuse)
⤷ most sensitive to diff. in light between center and surround of receptive field
31
explain: purpose dark adaptation experiment
- finding detection threshold for light at various intervals after bleaching
⤷ finding time it takes to recover from bleaching = reach max sensitivity
32
question: how long does it take rods to recover from bleaching? cones?
- rods = 20 - 25 mins
- cones = 5 mins
33
question: how does recovery from bleaching correlate w/ photopigment activity>
- activity dep. on rate of recovery
- cones recover quicker than rods
⤷ but rods have lower sensitivity threshold
34
explain: photopigment structure
- made in inner segment
- stored in outer segment
- has a prot. + a chromophore
⤷ prot = opsin = determines which wavelengths of light are absorbed
⤷ chromophore = absorbs light
35
explain: spectrophotometry
- measuring how much incoming light is absorbed by a prot.
- uses detector to see how much light isn't absorbed
⤷ remaining light = amount that got absorbed
36
question: how should a spectrophotometry experiment to test rod vision be done?
- should be run in dark conditions
⤷ so rods are at max sensitivity
- flash light at periphery (rods)
**spectral sensitivity found optimal = 500 nm
⤷ blue-ish
⤷ light absorp. by rods is best at 500 nm
37
question: how should a spectrophotometry experiment to test cone opsins be done?
- should be in normal lighting
- present light in center of vision
**spectral sensitivity found optimal = 550 nm
⤷ 3 types of cones each absorp. diff. wavelengths
⤷ overall = still 550
38
explain: distribution of cone pigments
- not equal among all cones
- 5 - 10% = S cones (short wavelength sensitive)
- remainder = 2:1 ratio for L cones : M cones
39
define: photochromatic interval
- diff. between just seeing light and being able to tell colour
⤷ how diff. does the intensity need to be
- how bright does it need to be to activate photopic vision (cones)
**on graph = y diff. between photopic curve and scotopic curve
40
define: purkinje shift
- diff. in perceived brightness of objects due to spectral shift
**on graph = diff. in x distance between peaks of scotopic and photopic curves
41
explain: scotopic and photopic sensitivity curves
- x axis = wavelength
- y axis = light detection sensitivity
DIFFERENCES
- blue wavelength = peak of scotopic, red = peak for photopic
⤷ means blue = brighter in low light, red brighter in photopic
- scotopic curve higher on y axis
⤷ means scotopic = more sensitive
peaks earlier
42
explain: dark current
- dark current = flow of cations into outer segment of pigment
- cyclic GMP binds to Na and Ca channels when dark
⤷ keeps channels open
⤷ allows Na and Ca into outer segment
- K leaves cell through inner segment
⤷ NaK pump keeps equil. between outside and inside
- dark membrane potential = -40 mV
⤷ higher than usual -70 mV
- glutamate constantly released from photoreceptor
43
explain: steps of phototransduction (6)
1. absorp. of light
2. rhodopsin changes conformation -> activated
3. activated rhodopsin activates G-prot (transducin)
4. G prot. activates PDE (enz)
5. PDE breaks down cGMP into GMP
6. cGMP channels close
**happens in light
⤷ opposes dark current
44
explain: inner nuclear layer of retina
- has bipolar cells
- synapse with rods/cones and pass signal to retinal ganglion cells
45
question: how does signal convergence differ in fovea vs periphery?
FOVEA
- few photoreceptors converge on a bipolar cell
- 1:1 ratio
- midget bipolar
PERIPHERY
- many signals converge onto bipolar cell
- pools info from many photoreceptors
- diffuse bipolar
45
explain: retinal ganglion cells
- in retinal ganglion cell layer of retina
- only neurons that leave the eye
- generate AP
46
question: how does a diff. in signal convergence impact acuity and sensitivity in fovea vs periphery?
- higher acuity in fovea bc 1:1 ratio
⤷ lower convergence
- higher sensitivity in peripheral
⤷ higher convergence
⤷ esp. in dim lighting
