Flashcards in Chromatic Aberration In The Human Eye Deck (72)
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1
What are monochromatic aberrations
Lower order aberrations
Higher order aberrations
2
What are the lower order aberrations that we normally deal with when correcting with glasses
Defocus and astigmatism
3
What kind of aberration can you correct with glasses
Lower order aberrations
4
What accounts for 90% of aberrations in the human eye
Lower order aberrations
(Defocus and astigmatism)
5
What are the higher order aberrations we normally deal with in the human eye
Spherical aberration
Coma
Trefoil
6
Can we correct higher order aberrations with glasses
No
7
What accounts for 10% of aberrations in human eyes
Higher order aberrations
8
What is monochromatic aberrations produced with
A single wavelength of light
9
When a mixture of different wavelengths of light (polychromatic light) are considered, then ______________ occur
Chromatic aberrations
10
The transmission speed of light within a refractive medium depends upon the wavelength
Dispersion
11
What is the refractive index for each wavelength in a refractive medium
Each is different
N=vc/Vmed
12
_______ wavelengths of light are more refracted than ________ wavelengths
Shorter
Longer
13
The separation of white light (polychromatic light) into its component elements by an optical element is referred to as ____________
Chromatic dispersion
14
Quantifies the amount of dispersions produced by an optical element
Dispersive power
15
What wavelengths are considered for dispersive power
486 (B)
589 (G)
656 (R)
16
What is the formula for dispersive power
w=(nf-nc)/nd-a)
17
What happens to the dispersion of the optical element (prism or lens) as the dispersive power increases?
It also increases
18
More or less dispersion causes more chromatic aberration?
More
19
What is the inverse of the dispersive power
Constrigence or Abbe number (v) of the refracting element
20
What happens to dispersion as the Abbe number increases
Decreases
21
Watch optical element is selected based on two important factors
-refractive index
-Abbe number
22
Which gets focused first, blue or red wavelength
Blue
23
How do we get the red and blue wavelength to focus on the same point
Glue two lenses together to create an achromat doublet
24
Is the eye a singlet or an achromat doublet
Singlet
25
What is an example of an achromat doublet
Video camera lenses and some optometry instruments
26
Dispersion of water
Not constant, but varies approximately 1% across visible spectrum (0.98%)
27
For dispersion, when the wavelength increases, what happens to the refractive index?
Decreases
28
What is the RI for blue wavelength (400nm)
1.343
29
What is the RI for the red wavelength (700nm)
1.330
30
Chromatic dispersion for the ocular media of the human eyes
0.02
Cornea, aqueous, vitreous all have similar RIs
Lens a little different
31
When the chromatic dispersion occurs, the image of source formed by blue rays will be formed in front of the image formed by the red rays. This chromatic difference of focus is called ____________
Longitudinal (or axial) chromatic aberration (LCA)
32
What is LCA specified by
The 'distance' between image planes
33
What is LCA measured in
Diopters
34
Longitudinal chromatic aberration (LCA) can be quantified in two ways:
1. The variation of power with wavelength-chromatic different of power
2. The vergences of source for which the source is focused at the retina for a range of wavelengths-chromatic difference of refraction
35
The variation of power with wavelength
Chromatic different of power
-a way to quantify LCA
-happens IN IMAGE SPACE
-not ideal to test patients this way
36
Of the two ways that LCA can be quantified, which one happens in image space
Chromatic difference of power
37
Chromatic difference of refraction
The vergences of source for which the source is focused at the retina for a range of wavelengths
-a way to quantify LCA
-happens in OBJECT SPACE
-ideal to test patients this way
38
Of the two ways you can quantify LCA, which one happens in object space
Chromatic differnce of refraction
39
Of the two ways to quantify LCA, which one is easier to test on patients
Chromatic difference of refraction
40
What do you need to test chromatic difference of refraction to find LCA?
-filters or laser to isolate red and blue light
-blue target
-get the blue target to focus and then put the red filter on and move it till its in focus, measure the distance between the two and thats the LCA
41
The variation of position of the image on the retina with wavelength is called _________
Transverse (or lateral) chromatic aberration (TCA)
42
What is TCA specified by
The angel between the refracted chief rays for different wavelengths
43
If you increase the angle, what happens to TCA
Increase
44
What are the two ways in which transverse chromatic aberration (TCA) be quantified
-the variation of postion with wavelength - chromatic difference of position
-the variation of magnification with wavelength- chromatic difference of magnification
45
Chromatic difference of position
The variation of position with wavelength
-a way to quantify TCA
46
For TCA, how is blue positioned compared to red
Below red
47
If the object is off axis, which can be measured, LCA or TCA?
BOTH
The off axis object is needed to measure TCA but you can still measure LCA with this
48
Chromatic difference of magnification
The variation of magnification with wavelength
-one of the ways to quantify TCA
-image on the retina for 400 and 700nm will be different magnifications
49
What axis does TCA=0?
Visual axis
50
What line do we use as a reference line for TCA
Achromatic axis
51
The angle between the visual axis and the achromatic axis
Is usually just a few degrees and is essentially zero for some individuals
52
What are the two types of abberations
Monochromatic
Chromatic
53
What are the types of monochromatic aberrations we deal with
Defocus
Astigmatism
Coma
Trefoil
Spherical aberration
54
What are the types of chromatic aberration we deal with
Longitudinal (LCA)
Transverse (TCA
55
What are the ways to quantify LCA
-Chromatic different of POWER
-chromatic difference of REFRACTION
56
What are the two ways we quantify transverse (TCA) aberration
-chromatic difference of POSITION
-chromatic difference of MAGNIFICATION
57
LCA between 400-700nm range is
About 2.1D
58
The human eye has too much power for
Shorter wavelengths
-too myopic
59
Studies of LCA
It is constant across all studies over 70 years
-2.1D
-the small variation in CA is because the main constituent of the ocular media is water, whose dispersion cannot vary between subjects
60
Why does the eye have too much power for shorter wavelengths
Human eye is more myopic for shorter wavelengths and so a negative spec Rx is required to correct this focusing error
61
LCA and age
LCA does not change significantly over the life span
-small changes in the RI of the eyes media which occurs with age leads to age-dependent changes in refractive error. However, the eyes chromatic aberration is determined by dispersions of the media rather than by the refractive index itself
62
What if chromatic aberration does change with age?
-important consequences for ocular measurement (optometer) and vision itself
-you would need different equipment for each age group
63
____ wavelength is usually in focus for low accommodation stimuli
Long
64
_____wavelgnths are in focus for higher accommodation stimuli
Short
65
What is blue light on the retina a cue for
Accommodation
66
What wavelength is associated with lead accommodation
Red
67
What wavelength is associated with lag accommodation
Blue
68
How does TCA vary
Unlike LCA, TCA varies in magnitude among studies and subjects
69
What does the magnitude of the TCA depend on
Field angle of the object (theta)
70
What is the averaged TCA across population
Zero
71
TCA for any given eye
NOT zero
-averaged TCA is zero, but not the TCA for any given eye
72
