Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

VF > Chapter 3 > Flashcards

Chapter 3 Flashcards

1
Q

Compare the attachment and phagocytization of discs in the rods and cones.

A

Rods- discs are free floating, phagocytize during the day
Cones- are fixed, phagocytize during the night

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where in the retina/brain do we have divergence of information?

A

From V1 (striate cortex)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the flow from optic nerve to tract to optic radiations. Where is there feedback?

A

LGN (synapse) to cerebral cortex into striate visual cortex AND extrastriate visual cortex separated by corpus callosum then to higher cortical areas (integration)

Feedback from higher cortical areas to V1 and LGN

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the range of light levels over which the visual system can function? What determines this range?

A

About 10 log units

Rods (scotopic) and Cones (photopic) (Duplex Retina)
Pupils account for about 1 log unit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe mesopic function.

A

Twilight
Area where both rod and cones are operating

Moonlit/Starlit paper

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

When do we have optimal acuity?

A

When the rods are saturated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe the properties of scotopic vision.

A

– Rod mediated
– Operates under nighttime lighting conditions
– High absolute sensitivity to dim light (only 10 quantal absorptions required)
– Poor contrast sensitivity
– Poor visual acuity (~20/200)
– Colorblind

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe the properties of photopic vision.

A

– Cone mediated
– Operates under daytime lighting conditions
– Poor absolute sensitivity to dim light
– High contrast sensitivity
– Good visual acuity (~20/20)
– Color vision

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the blind spot?

A

No PR in optic disc
15 degrees temporal to fixation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is retinitis pigmentosa?

A

Family of diseases causing damage to rods and cones
Can cause blindness
Allows waste to build up if phagocytization cannot occur
Scotopic usually affected first

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe retinal prostheses and how it can treat damaged retinal tissue.

A

Camera in spectacle sends image to microelectrode array on RNFL, or at site of retinal damage
Electrodes stimulate gc axons (bipolar cells) mimicking undamaged PR stimulation of GC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What occurs to the photoreceptors when it’s pigment absorbs a light quanta?

A

Hyperpolarizes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How much light can each molecule of rhodopsin absorb? How many quanta does it take to activate a rod?

A

One
One
Eye has a lot of rhodopsin (sensitivity)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does a molecule of rhodopsin become bleached? What is the max it can absorb, what happens after? How does it become unbleached?

A

When it absorbs light (one quantum of light)
Anything after one quantum is transmitted as a function of wavelength

Spontaneously (half life of 5 minutes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the reciprocal of the transmission curve?

A

Absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

According to the absorption curve, when is a molecule of rhodopsin MOST likely to be absorbed?
When is a molecule most likely to be transmitted?

A

At 507nm

At 500nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Define univariance.

A

Once rhodopsin absorbs light all information about the quantum of light is gone
Effects of the different wavelengths are now the same
(Wavelength affects probability of absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why does the scotopic spectral sensitivity function have the same shape as the absorption function?

A

The human scotopic sensitivity function is determined by absorption characteristics of rhodopsin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What percentage of quanta incident on the retina are actually absorbed?

A

20% b/c most is reflected or absorbed by other tissue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Is sensitivity the reciprocal of threshold?

A

Yes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

As threshold increases what happens to sensitivity?

A

Decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How is the scotopic spectral sensitivity function measured? Define threshold.

A

Patient sits in totally dark room to allow rhodopsin to regenerate
We flash a stimulus to determine the sensitivity
The minimum amount of energy needed to detect stimuli is threshold

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are the 3 classes of cones?

A

L-cones: contain erythrolabe (red, long, peak @426nm)
M-cones: contain chlorolabe (green, middle, peak @530nm)
S-cones: contain cyanolabe (blue, short peak @557nm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Which cones contribute to the photopic spectral sensitivity function? Where does it peak? How is it performed?

A

L and M
Peak @555nm
Measured under brighter lighting conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How does the regeneration of cone pigments after bleaching compare to rhodopsin?

A

Half life of 1.5 minutes for 50% recovery
Faster than rhodopsin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the Purkinje Shift?

A

The relative increase in the brightness of longer wavelengths stimuli as lighting condition change from scotopic to photopic

Wavelength to which we are most sensitive changes from 507nm to 550nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How are scotopic and spectral sensitivity curves plotted together?

A

Functions are determines after the subject was stirring in the dark and rhodopsin and cone pigment regenerated

28
Q

Describe the photochromatic interval.

A

Difference between scotopic and photopic sensitivity for a given wavelength

Smaller at longer wavelength

First the threshold scotopic is recorded (stimulus detection with no color vision) then photopic (color detection)

29
Q

The scotopic system is more sensitive then the photopic except at:

A

650nm

After 650nm photopic is slightly more sensitive

30
Q

What components contribute to the excellent resolution at the fovea?

A

Absence of rods
Maximal density of cones
Pushing aside of inner retinal element to expose outer segments to light
Absence of retinal vasculature

31
Q

Are there any rods in the fovea?

A

NO cones only

Rods peak at 20degrees from fovea

32
Q

Are there cones in areas other then the fovea?

A

Yes

Less then 5% of cones are actually in fovea but they are very dense there

33
Q

What happens to rids and cones as we age?

A

Cones stable with age
Rods decrease with age

34
Q

What cone types are concentrated at the fovea?

A

L and M
Distribution varies greatly with individual (does not necessarily affect color vision)
S cones are less numberous, moreso at the slopes of the fovea peaking at .5 degrees

35
Q

How is the dark adaptation curve generated?

A

Photopigments are bleached with bright adapting light, after lights are turned off the visual threshold decreases
Stimulus (420nm, 10 degree, 3 log units) flashed on dark background in dark room

36
Q

How do rods and cones compare in sensitivity?

A

Rods and cones recover sensitivity at different rates, the rods take over after about 85% of the rhodopsin has recovered.

Cones recover faster, rod cone break, rods take over become sensitive, less light is required as time progresses

37
Q

What is the photochromatic interval of the dark adaptation curve?

A

The difference between plateaus

38
Q

Will patient be able to see color after 5 minutes? After 30 minutes?

A

Yes because threshold is determined by cones

No b/c threshold is detected by scotopic, cones are still there but stimulus is too dim

39
Q

How does the dark adaptation curve look if the stimulus is 650nm?

A

At 650nm rods and cones have the same sensitivity
There is no photochromatic interval (zero), no rod cone break (longer wavelength, smaller rod cone break)

Only one cone portion, rod aspect is missing

40
Q

How does the dark adaptation curve look if the stimulus is very small (0.5 deg) and centrally fixed?

A

No rods, curve represents the cones, no rod cone break
Stimulus is small, confined to fovea (cones only)

41
Q

Is light adaptation a slow or rapid procedure?

A

Rapid
Appearance of objects remains the same when we step out into bright environments because the visual system adapts to changes in illumination levels

42
Q

How is the increment threshold used to study light adaptation?

A

Threshold is detained for a flash of light (increment) on a dark background of a given intensity
Repeatedly the background intensity is increase and the stimulus flashed until background is extremely bright

43
Q

Describe the light adaptation curve. What happens at m=1 and after?

A

Under scotopic
Rods only
At m=1 Weber’s law is displayed, as the background brightness is increased, the increment intensity must also increase so the ratio is constant and for the increment to be visible
Once it is no longer visible the Rods can’t hyperpolarize anymore, become saturated, can’t operate, only 10% is bleached

44
Q

What is the equation for Weber’s Law? What is Weber’s constant for scotopic and photopic vision?

A

Delta I = K lb
K= delta I / Ib
K= Webers constant

For scotopic vision, K = 0.14
For photopic vision, K = 0.015

45
Q

Describe sensitivity regulation and how we are able to maintain Weber’s constant?

A

Although the relative sensitivity of the visual system (0.14) does not change as the illumination increases, there is a reduction in the absolute sensitivity (the threshold goes from 14 to 140 units).
(Threshold contrast remains constant)

46
Q

According to Weber’s constants how do rod and cones compare in sensitivity to contrast and absolute sensitivity?

A

photopic system is about 10 times more sensitive to contrast than the scotopic system (0.015 vs 0.014)

Photopic system absolute sensitivity is less

47
Q

Hoes does the orientation of rods and cones in the retina explain the fact that photopic condition don’t automatically mean better V/A?

A

Rods are connected in such a manner as to sum up information over space. This produces great sensitivity, but poor resolution.

Cones, on the other hand, manifest connections that maximize visual resolution at the expense of sensitivity.

48
Q

What is spatial summation?

A

scotopic system, to a greater extent than the photopic system, sums up information over space—it manifests greater spatial summation because more rods synapse onto a single ganglion cell

49
Q

Compare the spatial summation and resolution of scotopic and photopic.

A

scotopic system: excellent spatial summation contributes to its high sensitivity, but results in poor spatial resolution. (Ex: we can see a dim star at night, yet have a scotopic acuity of only 20/200)

photopic system: less spatial summation, resulting in poor sensitivity, but excellent spatial resolution (20/20)

50
Q

Describe the temporal summation and result ion of the scotopic system.

A

The scotopic system manifests excellent temporal summation, but poor temporal resolution.

51
Q

Is the scotopic or photopic better able to distinguish two flashes of light overtime?

A

Photopic

52
Q

What will be seen what 2 stimuli are under threshold and outside of the temporal summation period (scotopic)?

A

No flash

53
Q

What will be seen if two stimuli are under threshold and within the temporal summation period (scotopic)?

A

One flash

54
Q

What will be seen if 2 stimuli are above threshold and within temporal summation period (scotopic) ?

A

One flash

55
Q

What will be seen if 2 stimuli are above threshold and outside of TSP (scotopic)?

A

2 flashes

56
Q

Describe the temporal resolution and summation under photopic conditions.

A

The photopic system manifests excellent temporal resolution, but poor temporal summation.

57
Q

What will be seen if 2 stimuli are under threshold outside of TSP (photopic)?

A

No flash

58
Q

What will be seen if 2 stimuli are under threshold within TSP (photopic)?

A

One flash

59
Q

What will be seen if two stimuli are above threshold outside of TSP (photopic)?

A

Two flashes

60
Q

How does the angle at which a light ray strikes the photoreceptors important?

A

Important for cones not so much rods
With centered pupil, cones that most effecting pigment bleach and a brighter stimulus perceived
Scotopic have the same brightness regardless of angles

61
Q

During what instance do the cone change their orientation?

A

With CL cones point to decentered pupil

62
Q

What can we make when increment sensitivity is determined for many different points?

A

VF (done under photopic conditions)

Critical for managing glaucoma
Stimulus for VF is increment on background

63
Q

Where is the blind spot as related to the fixation point?

A

Temporal and inferior

64
Q

Describe the dark adaptation curve with congenital stationary night blindness?

A

Threshold plateaus instead of declining over time

65
Q

What is a AdaptDx Dark Adaptometer used for?

A

To assess ARMD
Allows fast determination of dark adaptation curve

66
Q

How does an early cataract affect the increment thresholds measured during visual fields?

A

Cataracts causing increments intensity to decrease on retina, K remains constant therefore the measured threshold remains the same

VF (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions