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Optics BLOCK 3 > Optical Abberations > Flashcards

Optical Abberations Flashcards

1
Q

Higher order aberrations

A

What’s left after you take away the defocus and astigmatism

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2
Q

What can reduce higher order aberrations?

A

Reducing pupil size

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3
Q

Plane wavefront

A

Parallel beam

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4
Q

Spherical wavefront

A

Converging beam

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5
Q

Aberrated beam

A

Irregular wavefront

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6
Q

Aberrations

A

Failure for the light rays passing through an optical system to converge at one point. Possibly due to defects or limitations of the system

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7
Q

Lower order aberrations

A

Piston
Title
Astigmatism
defocus

Usually can always be corrected with glasses

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8
Q

Higher order aberrations

A 
Trefoil
Coma
Spherical 
Tetrafoil 
Pentafoil
Hexafoil
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9
Q

Zernike polynomials

A
  • set of basic shapes that are sued to fit the wavefront

- analogous to the parabolic X^2 shape that can be use to fit 2D data

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10
Q

Orthogonal

A

Terms are not similar in any way, so the weighting of one term does not depend on whether or not other terms are being fit also

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11
Q

Normalized

A

The RMS wave aberration can be simply calculated as the vector of all or a subset of coefficients

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12
Q

Efficient

A

Zernike shapes are very similar to typical aberrations found in the eye

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13
Q

Picturing astigmatism

A
  • 2nd order

- 2 different focal planes

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14
Q

Conoid of sturm

A

Shows the two planes where there is perfect focus and the half way point of those as well

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15
Q

Sturms interval

A

The distance between the two planes of perfect focus in the conoid of sturm

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16
Q

Circle of least confusion

A

The area right between the two planes where there is perfect focus

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17
Q

Aberrations in imaging media

A 
Piston
Tilt
Defocus
Spherical aberration
Coma
Astigmatism
Field curvature
Image distortion
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18
Q

What is the only aberration that occurs for both on-axis and off-axis object points?

A

Spherical aberration

-the thickens of the lens is different between the top and bottom and center, there will be spherical aberration

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19
Q

Positive and negative spherical aberration

A

Shows peripheral rays intersecting closer to the lens

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20
Q

What kind of eclipse does LASIK create?

A

Oblate

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21
Q

Coma aberration

A

Comet shaped pattern caused by off-axis point source passing through a spherical system

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22
Q

What eye disorder often has a lot of coma aberration?

A

Keratoconcus

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23
Q

What kind of aberration do they often find in pilots?

A

Vertical coma

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24
Q

Oblique, marginal, or radial astigmatism

A
  • light coming from off axis (aberration, not talking about Rx)
  • passing through cylindrical correction
  • bending sunglasses around face induces cylinder, as does pantoscopic tilt
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25
Q

Field curvature/distortion

A

Focused on a curved surface

-petzval surface

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26
Q

Distortion shapes

A

Barrel and pincushion

-look exactly like what you would think

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27
Q

Resolution

A

The point where you can resolve two points

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28
Q

Unresolved

A

Two dots that look like one

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29
Q

Resolved

A

Two dots that can be differentiated as two dots

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30
Q

Rayleigh criterion

A

The point between resolved and unresolved.

-its the very beginning of being able to see two different dots, a threshold sorta

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31
Q

What is considered to be about the perfect pupil size?

A

2mm

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32
Q

Does resolution get worse to better when pupil gets smaller?

A

It gets better to a certain point and then it gets worse

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33
Q

What kind of limit is there when the pupil gets smaller?

A

Diffraction

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34
Q

How many arc minutes in a 20/20 E?

A

5 minutes

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35
Q

How many cycles in a 20/20 E?

A

30 cycles/degree

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36
Q

Airy disk and airy pattern

A

Descriptions of the best focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light
-as pupil gets smaller, you get this

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37
Q

What is one limitation of the image quality of an optical system?

A

Airy disk

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38
Q

If you want better resolution what type of lens should you use?

A

Sometimes, the bigger the lens, the better the resolution

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39
Q

What does diffraction do to light?

A

Causes it to bend perpendicular to the direction of the diffracting edge

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40
Q

What does interference do to light?

A

Causes the diffracted light to have peaks and valleys

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41
Q

What does a modulation transfer function compare?

A

Contrast and resolution

42
Q

High resolution

A

How small you can see

43
Q

High contrast

A

Color

44
Q

With 20/20 vision the contrast

A

Will be higher (tighter), high frequency

45
Q

Modulation transfer function

A

Indicates the ability of an optical system to reproduce (transfer) various levels of detail (spatial frequencies) from the object to the image

46
Q

What are the units of a modulation transfer function?

A

Ratio of image contrast over the object contrast as a function of spatial frequency

47
Q

What is the optical contribution to the contrast sensitivity function?

A

Modulation transfer function

48
Q

How many cylces per degree are in a 20/20 E?

A

30

49
Q

How many cylces per degree are in a 20/10 E?

A

60 c/d

50
Q

More than 60 c/d

A

Not really necessary

51
Q

cut off frequency

A

Increases by ~30c/d for each mm increase in pupil size

52
Q

What does adding even a little bit of defocus to a “perfect eye” do?

A

Drastically changes vision, but helps with depth of field

53
Q

What does more cycles/degree mean?

A

Better vision

54
Q

1 cycle =

A

2 degrees

55
Q

1 degree equals

A

60 minutes
And
30 cycles

56
Q

the PSF is the

A

Fourier transform (FT) of the pupil function

57
Q

The MTF is the

A

Amplitude of component of the FT of the PSF

58
Q

The PTF is the phase component of what

A

Of the FT of the PSF

59
Q

What does coma wave front aberration and point spread function look like?

A

Look on life 70

60
Q

Shack-Hartmann wavefront sensor

A

Can tell the shape of the wavefront

61
Q

Fitting the wavefront in the shark hartmann wavefront sensor

A
  • the local slope of the wavefront I determined at each lenslet location
  • corresponding wavefront is determined by a least squares fitting of the slopes to the derivative of a polynomial selected to fit the wavefront
  • zernike polynomial is the most commonly used
62
Q

What is the most commonly used polynomial for shack hartman wavefront sensor?

A

Zernike polynomial

63
Q

What is determined at each lenslet location in the shake hartman wavefront sensor?

A

Local slope

64
Q

What is the corresponding wavefront determined by in the shark hartman wavefront sensor?

A

By a least squares fitting of the slopes to the derivative of a polynomial selected to fit a wavefront

65
Q

What kind of pattern do people see at night after RK?

A

Star

66
Q

What kind of pattern does a LASIK patient see at night?

A

Ring

67
Q

What can cause glares, haloes, scattering?

A

Dry eye, cataracts

68
Q

iris tears can cause what?

A

Scattering

69
Q

Age and glare

A

Increases with age (cataracts)

70
Q

What are the metrics to define image quality

A
  • wavefronts
  • zernike terms
  • root mean square
71
Q

Root mean square wave aberration

A

Square each number, add up the squared number, and then take the square root of that number

72
Q

Strehl ratio if pupil is small

A

Would be close to 1, could be 0.5 for large

73
Q

What is the normal strehl ratio?

A

5%

74
Q

What is strehl ratio

A

Point spread function

75
Q

What will the area under the MTF if you have worse vision?

A

Smaller

76
Q

MTF

A

Spatial frequency on X

Contrast on Y

77
Q

Convolution

A

Adding a PSF on every corner of the E to see what someone with that aberration would be seeing

78
Q

Strehl ratios for a 5mm pupil

A

Are about 5% for a 5mm pupil that has been corrected for defocus and astigmatism

79
Q

Strehl ratios for a small pupil

A

Approach 1, but the image quality is poor due to diffraction

80
Q

When do aberrations diminish?

A

Like most optical systems, they diminish as the aperture is reduced

81
Q

Overall the eyes high order abberations ____with pupil size.

A

Reduce

82
Q

Dynamic changes in the wave abberations are caused by

A
  • accommodation
  • eye movement
  • eye translation
  • tear film
83
Q

Change in abberations with age

A

Increase

84
Q

What can increase the depth of field?

A

Negative spherical aberration

85
Q

Custom IOL for abberations

A

Go in after cataract surgery and use light to adjust wavefront correction after the surgery

86
Q

Presbyopia relief

A

Bifocal lenses do not always provide bifocal vision

87
Q

Emmetropization

A

Born hyperopic and shift towards emmetropization

88
Q

What kind of abberations decrease with age?

A

Higher order

89
Q

Adaptive optics

A

Deformable mirror takes shape of wavefront so that it refracts straight
-measure the wavefront

90
Q

What does adaptive optics do to the wave aberration?

A

Flattens it

91
Q

Real time adaptive optics

A

Tear film can change it, needs to be real time

92
Q

How well can someone see with adaptive optics?

A

Can get someone to see 20/7

93
Q

Adaptive optics and retinal image quality

A

It improves retinal image quality

94
Q

Basic science imaging applications of adaptive optics

A
  • reveal properties of single cells in living eyes
  • correlate properties of cellular structure in living eyes with visual performance
  • nonlinear imaging of structure and function
95
Q

Pre-clinical applications of adaptive optics

A
  • facilitate longitudinal tests on animal models
  • test outcomes of drugs and treatments for eye disease
  • correlate phenotype with genotype in animal models of eye disease
96
Q

Clinical applications of AO

A
  • provide early dx for retinal or other systemic disease
  • better understand the etiology of retinal disease for which little is known
  • discover more sensitive biomarkers for retinal disease
  • track progression of eye disease
  • measure response at a cellular levels to therapies that treat disease
  • preselect patietns or diseases that may benefit best from therapies or treatments
97
Q

Tracking cones

A

Use AO to track a cone over time to see how well treatment is working
-can also monitor cone density

98
Q

Functional imaging applications of AO

A
  • facilitate better relationships between structure and function
  • reveal properties of cell networks in living eyes
99
Q

Vision applications of AO

A
  • pre-test the benefits of aberration correction on vision
  • develop optical aberration profiles for long depth of focus
  • test possible signals that drive accommodation and/or eye growth
  • reveal the optical retinal and neural limits of human vision
100
Q

What is Dr. H’s study?

A

Optical aberration profiles for long depth of focus

101
Q

Light delivery applications of AO

A
  • track and stimulate single cells or networks of cells for electrophysiology expts
  • microperimetry
  • targeted laser treatment
  • track eye movement responses to stimulation
  • study role of eye movements for vision

Optics BLOCK 3 (4 decks)

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