Chromatic Aberration In The Human Eye Flashcards Preview

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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

Mean magnitude of foveal TCA for red and blue light is

0.82arcmin of visual angle