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Optics Block 7 > Chromatic Aberrations In The Human Eye > Flashcards

Chromatic Aberrations In The Human Eye Flashcards

1
Q

What are the types of monochromatic aberrations

A 
Defocus
Astigmatism
Coma 
Trefoil 
Spherical aberration
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2
Q

What are the chromatic aberrations

A

Longitudinal (LCA)

Transverse (TCA)

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3
Q

What are the two things we care about in LCA

A
  • Chromatic difference of power (focus, defocus, blur..)

- chromatic difference of refraction

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4
Q

What two things do we care about in transverse chromatic aberration (TCA)

A
  • Chromatic difference of position

- chromatic difference of magnification

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5
Q

What is said about the stimulus if red is focused on the retina

A

It is low stimulus, object far away

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6
Q

What is said of the stimulus of the blue is in focus

A

Object is close, high stimulus

-may cue accommodation

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7
Q

Significance of chromatic defocus (LCA) depends on what

A

Luminance

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8
Q

What does the autorefractor measure people

A

Hyperopic

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9
Q

What is the LCA average (distance from red to blue)

A

2.1D

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10
Q

At what wavelength do people become hyperopic

A

580nm

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11
Q

What happens to the refractive error with higher wavelengths

A

Increases

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12
Q

What do short wavelengths make people

A

Myopic

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13
Q

What do long wavelengths do to people

A

Make them hyperopic

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14
Q

The chromatic difference of focus (CDF) reduces retinal image contrast by _____ of defocus

A
  1. 2D

- relatively minor

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15
Q

What is the amount of defocus in the chromatic difference of defocus equivalent to

A

The amount of defocus is equivalent to the depth of field of the human eye

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16
Q

What does the chromatic difference of focus do for vision

A

Reduces contrast moderately

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17
Q

Effect of chromatic defocus on VA

A
  • Minor effect on the VA

- any attempt to correct would only provide marginal benefit and surface new problems

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18
Q

The chromatic difference of magnification for two wavelengths of light has what kind of relationship with the axial distance (z) from the pupil to nodal point

A

Proportional

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19
Q

What is the equation for the chromatic difference of magnification

A

Change in mag=z(2D)

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20
Q

What is the change in mag usually

A

0.8%

Considered insignificant

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21
Q

What does the magnitude of the effect depend on

A

Axial distance Z

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22
Q

When can magnification be 0

A

Only if the pupil and nodal point are at the same place

0 axial length

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23
Q

What is the axial length we look at for magnification

A

Pupil to nodal point

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24
Q

When is magnification significant

A 
Looking through optical instrument. 
Depth perception (3D glasses)
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25
Q

CDM (chromatic difference in mag) and depth perception

A

Red and blue have different focuse and magnification.
-if one eye view through short wavelength light, the visual system may interpret the different sized retinal images as a difference in relative depth resulting in a distorted perception of 3D world

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26
Q

The chromatic difference of position is directly proportional to

A
  • stimulus eccentricity (certain field angle)

- lateral displacement (foveal vision)

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27
Q

How much is the pupil decentered

A

0.5mm nasally

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28
Q

CDP (chromatic difference of postion) for stimulus eccentricity

A

For object points off the achromatic axis, the amount of TCA as a function of axial location of pupil z, CD-R, and the angle of eccentricity

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29
Q

What happens when you increase eccentricity to TCA?

A

Increases it just slightly

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30
Q

Equation for stimulus eccentricity

A

TCA=(z)sin(e)(2D)

Z=axial length
E=eccentricity
2=given, LCA

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31
Q

Chromatic difference of position induces ________________ which affect image contrast (visual performance)

A

Wavelength depends spatial phase shifts

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32
Q

What does chromatic phase shift affect

A
  • defining color

- luminous contrast in the image

33
Q

CDP (chromatic difference position) for displaced pupil

A

If the limiting aperture is displaced by amount ‘h’ from the visual axis, then the magnitude of TCA present at the fovea is

h(2D)

34
Q

What does a 1mm displaced pupil do to TCA

A

There is 7.2arcmin of TCA

35
Q

1mm of displacement of external pupil is equivalent to ____ of eccentricity for the naked eye. Both generate same amount of TCA

A

15 degrees

36
Q

What is a major limiting factor for foveal vision

A

Displaced aperture
-limitations due to ocular chromatic aberrations may arise due to clinical assessment of visual function using a misaligned optical instrument with respect to the visual axis

37
Q

Effect of TCA on VA

A

-the ocular chromatic aberration accounts for most of the acuity loss suffered when viewing through a displaced pupil

38
Q

The vVA drops from 20/20 to 20/60 when the test instrument is displaced _____ from the visual axis

A

3mm

39
Q

What will all points on the retina image suffer

A

From the combined effect of lCA and TCA

40
Q

What point on the retina will it not suffer from combined effects of LCA and TCA

A

The location on the retinal image when eyes achromatic axis intersects with the retina where TCA=0

41
Q

LCA reduces image contrast how

A

Blur

42
Q

TCA reduces image contrast how

A

By inducing phase shifts

43
Q

Which reduces image contrast more, LCA or TCA?

A

TCA

44
Q

What happens when the pupil is displaced

A

A large amount of TCA results, causing the image to be spread out horizontally like a tiny rainbow

45
Q

When the pupil is displaced and you are myopic, what color will be in focused when a white light source is shown

A

Green

46
Q

When the pupil is displaced and you are hyperopic, what color will be in focus if a white light source is shown to you

A

Red

47
Q

If the pupil is displaced and you are emmetropic, what color will be in focus when you see a white light source

A

Yellow

48
Q

What happens to VA if you increase target vergence (increase defocus)

A

Decreases

49
Q

What could help lessen the affect of that increased target vergence has on VA?

A

Corneal inlay

50
Q

How large is a corneal inlay

A

1.6mm

51
Q

What happens if the inlay is displaced even 1-2mm

A

Dramatic VA decrease

52
Q

What is a good way to reduce displacement of a corneal inlay

A

Use perkinje 1 when laying inlay
-you will still get chromatic aberration
0use aberrometer and make sure TCA=0 during surgery

53
Q

A point object emitting two wavelengths of light will produce a double retinal image whihc gives rise to the perception of a double object, a condition called

A

Chromatic diplopia

54
Q

Chromatic diplopia is the basis for what

A

Chromostereopsis

55
Q

A stereoscopic illusion in which a differently colored object located at the same viewing distance appear to lie at a different distance (3D movies)

A

Chromostereopsis

56
Q

________ is an effect of TCA combined with binocular vision

A

Chromostereopsis

57
Q

In chromostereopsis, what color appears closer

A

Red

58
Q

What is a good example of chromostereopsis?

A

Stained glass trans illuminated by sunlight

59
Q

In chromostereopsis, if the pupil is displaced temporally, what color will appear closer

A

Red

60
Q

In chromostereopsis, if the pupils are displaced nasally, what color appears closer

A

Blue

61
Q

What two things can we fix that will give us the minimum creation to VA

A

Defocus + astigmatism (lower order aberrations)

62
Q

What thing that if we could fix, would correct our VA the best

A

Higher order monochromatic aberrations + chromatic aberrations

63
Q

When only monochromatic aberrations are corrected, the contrast sensitivity of the eye is improved by a factor of

A

2

64
Q

When only monochromatic and chromatic aberrations are corrected, the contrast sensitivity of the eye is improved by a factor of

A

3.2 to 5

65
Q

Optical elements are based on

A

Abbe number and refractive index

66
Q

What quantity of light a material disperses

A

Abbe number

67
Q

Is it better to have a higher or lower abbe number

A

Higher

68
Q

Separation of white light into component elements is referred to as

A

Chromatic dispersion

69
Q

Dispersion of water accounts for about _____ across visible spectrum according the water eye model

A

1%

70
Q

Variation of power with wavelength is chromatic difference of

A

Power (focus, blur, defocus)

-LCA

71
Q

Power of ______ when measuring in object space

A

Refraction

72
Q

Power of ____ when measuring on retina

A

Power

73
Q

TCA may be specified by ____ for a different wavelength

A

Angle

74
Q

True or false, TCA of the human eye does not change over life

A

True

75
Q

Change in chromatic berration is determined by _____ of medium

A

Dispersions

NOT RI

76
Q

Determine chromatic difference of magnification if axial distance is 0.25

A
  1. 25 X 2

0. 50

77
Q

Changes at different positions induces _____ which affect image contrast

A

Phase shift

TCA

78
Q

When viewing a trans illuminated stained glass window, if the chromostereopsis makes blue appear close, the pupils re displaced how

A

Nasally

79
Q

What does the epsilon in the equation for CDP by eccentric stimulus stand for

A

Eccentricity

=zsin(E)(2.1)
Convert to arc min!

Optics Block 7 (6 decks)

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