1
Q
What allows the human eye to see bright and feeble light?
A
The pupil changes its diameter in response to light, controlling the amount of light that falls upon the retina.
2
Q
What is the log unit range of retinal illuminance?
A
10-log unit range
3
Q
How much of the retinal illuminance log unit adaptation is accounted for by changes in pupillary diameter?
A
1 log unit out of 10 log unit range
4
Q
What accounts for the remaining adaptation of retinal illuminance?
A
Rods and cones
5
Q
Scotopic vision occurs under what lighting conditions?
A
Dim
6
Q
What is the visual acuity of scotopic vision?
A
Poor 20/200
7
Q
Is color discrimination possible with scotopic vision?
A
No, it is absent.
8
Q
What mediates scotopic vision?
A
Rods
9
Q
Photopic vision occurs under what lighting conditions?
A
Bright
10
Q
What is the sensitivity of photopic vision to dim lights?
A
Poor
11
Q
What is the visual acuity of photopic vision?
A
Excellent 20/20
12
Q
Is color discrimination possible with photopic vision?
A
Yes
13
Q
What type of vision do cones mediate?
A
Photopic/color
14
Q
What is the term for the existence of two classes of photoreceptors operating under different lighting conditions?
A
Duplex retina
15
Q
Under twilight (Mesopic) conditions, which photoreceptors contribute to vision?
A
Rods and cones
16
Q
What is the rod photopigment?
A
Rhodopsin
17
Q
How many rods does one eye contain?
A
About 120 million rods
18
Q
How many disks does each rod contain?
A
About 1000
19
Q
How many rhodopsin molecules are in each disk?
A
About 10,000
20
Q
How many photons of light can each rhodopsin molecule absorb?
A
One
21
Q
What conditions do a large number of rhodopsin molecules contribute to sensitivity?
A
Nighttime
22
Q
What happens to light quanta that are incident on rhodopsin but not transmitted?
A
They have been absorbed.
23
Q
What wavelength (nm) has the highest probability of absorption in rods?
A
507 nm
24
Q
What happens to all information regarding a quantum of light’s wavelength once it is absorbed?
A
It is lost.
25
What is the term for the principle that describes the loss of wavelength information upon light absorption?
Univariance
26
What happens to a molecule of rhodopsin when it absorbs light?
It becomes bleached.
27
What is required to bleach a molecule of rhodopsin?
The absorption of only one quantum of light.
28
When a rhodopsin molecule is in the bleached state, can it capture another quantum?
No, it is not capable.
29
What percentage of rhodopsin will recover in 5 minutes?
50% - half-life for rhodopsin
30
What is the physiological response of the visual system to 1000 quanta of 507 nm light compared to 680 nm light?
The same response to 2000 quanta.
31
Does the scotopic system have wavelength discrimination?
No, it is colorblind.
32
What is the minimum amount of energy required for detection of a stimulus called?
Threshold
33
What is the sensitivity curve the reciprocal of?
Threshold function
34
What does a low threshold indicate?
High sensitivity
35
What determines the human scotopic spectral sensitivity function?
The absorption characteristics of rhodopsin.
36
How many quantal absorptions may be sufficient to activate one rod?
Ten, but they must occur within certain space and time constraints.
37
What are the three cone photopigments?
Blue, Green, Red
38
What is the wavelength for blue cones?
426 nm
39
What is the wavelength for green cones?
530 nm
40
What is the wavelength for red cones?
557 nm
41
How many photopigments does each cone contain?
One
42
What does the photopic spectral sensitivity curve show?
A single broad peak in the region of 555 nm.
43
Under what conditions can the photopic spectral sensitivity curve be determined?
Brighter conditions
44
Do S-cones make a significant contribution to spectral sensitivity?
Very little contribution.
45
What is the difference in sensitivity between scotopic and photopic systems for a given wavelength called?
Photochromatic interval
46
When is the scotopic system more sensitive than the photopic system?
At all wavelengths except in the long-wavelength (red) region.
47
What does a photochromatic interval of approximately zero mean?
Rods and cones are almost equally sensitive.
48
Beyond 650 nm, how does the photopic system compare to the scotopic system?
It is slightly more sensitive.
49
How do photochromatic intervals change with retinal eccentricity?
They increase.
50
What happens to interval size for short and medium wavelengths toward the peripheral retina?
It increases at a negative rate.
51
What happens to interval size for long wavelengths toward the peripheral retina?
It increases at a positive rate.
52
As lighting conditions change from scotopic to photopic, what does the wavelength sensitivity increase from and to?
From 507 to 555 nm.
53
What is the relative increase in brightness of longer wavelength stimuli as lighting conditions change from scotopic to photopic called?
Purkinje shift
54
Is the ratio of L- to M-cones constant from person to person?
No, it varies.
55
What percentage of the cone population do S-cones constitute?
3-5%
56
What are the four mechanisms used to allow the visual system to operate over a range of retinal illuminance levels?
1. Changes in pupil size
2. Rods and cones
3. Changes in concentration of bleached and unbleached photopigments
4. Changes in neural responses
57
What is the process that decreases threshold luminance as a function of time in darkness?
Dark adaptation
58
What is the process that increases threshold luminance in response to increased illumination?
Light adaptation
59
What do rods and cones recover at different rates after exposure to bright light?
Sensitivity
60
What is recovery in rods and cones related to?
The regeneration of photopigment molecules.
61
What are the two steps of dark adaptation by psychophysical threshold technique?
Step one: expose the eyes to a supra-threshold adapting light.
Step two: turn off the adapting light and present a test flash.
62
How much does the threshold reduce in rods over a period of 35 minutes in the dark?
5 log units
63
After 35 minutes in the dark, how much more light sensitive is the eye?
100,000 times more light sensitive.
64
What does a higher threshold indicate?
Lower sensitivity.
65
Are rods or cones more sensitive to light?
Rods are more sensitive to most wavelengths of light.
66
At what percentage of rhodopsin regeneration do rods become more sensitive than cones?
90%
67
What is the rod-cone break?
The point in time when rods become more sensitive than cones.
68
What is the photochromatic interval?
The difference between the cone plateau and the rod plateau.
69
What does the cone plateau represent?
Minimum photopic threshold for a stimulus.
70
What does the rod plateau represent?
The minimum scotopic threshold for a stimulus.
71
What factors affect the shape of the dark adaptation curve?
Retinal location, size of test flash, wavelength of adapting light, wavelength of test flash, intensity of adapting light, duration of adapting light, and task performance.
72
What form does the dark adaptation curve take if the stimulus is 650 nm?
It shows only a cone portion because the photochromatic interval for 650 nm is zero.
73
Are rods more sensitive than cones for long wavelengths?
No.
74
What is the visual system's ability to adapt to changes in illumination levels?
Light adaptation
75
How may light adaptation be studied?
With an increment threshold procedure.
76
What does the light adaptation curve show?
Increment threshold as a function of background adapting intensity.
77
What is the Weber fraction for scotopic vision?
0.14
78
What is Weber's law with scotopic light adaptation?
The slope of the curve is equal to 1 and the ratio of increment intensity to background intensity remains constant.
79
If the background intensity is 100 units, what must the increment intensity be to be detected?
14 units
80
If the background intensity is 1000 units, what must the increment intensity be to be detected?
140 units
81
How does absolute sensitivity change as illumination increases?
There is a reduction in absolute sensitivity.
82
What is the tradeoff between relative and absolute sensitivity called?
Sensitivity regulation.
83
What is the Weber fraction for photopic vision?
0.015
84
How much more sensitive is the photopic system to contrast compared to the scotopic system?
10 times more sensitive.
85
Where are cones mostly concentrated?
Fovea
86
Where are rods concentrated?
Periphery of the retina
Block 09
flashcards
Decks in class (33)
# Cards
-
Epi: Introduction126
-
Mono: Photometry And Radiometry79
-
Pharm: Introduction14
-
Pharm: Pharmodynamics93
-
Mono: Lightness36
-
Mono: Sources and Filters46
-
Epi: Transmission Of Disease90
-
Pharm: Pharmacokinetics 192
-
Pharm: Pharmacokinetics 255
-
Mono: Duplex Retina86
-
Micro: Introduction To Viruses74
-
Micro: dsDNA Viruses134
-
Micro: HepaDNAvirus25
-
Micro: ssDNA viral pathogens14
-
Micro: (+)ssRNA enveloped viruses136
-
Epi: Disease Occurence77
-
pharm: pharmacokinetics 343
-
pharm: pharmacokinetics 461
-
pharm: pharmacokinetics 556
-
micro: naked (+) ssRNA viruses43
-
mono: spatial resolution and summation59
-
mono: spatial vision75
-
mono: clinical implications to CSF39
-
mono: temporal vision59
-
pharm: pharmacogenomics36
-
micro: -ssRNA and -dsRNA viruses122
-
micro: retroviruses and prions36
-
epi: ocular and systemic disease and disorders148
-
Micro: Virus review121
-
Mono: Motion Perception80
-
Mono: Depth Perception51
-
Epi: Epidemiology In Appalachia18
-
Micro: Flora96
