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Optics 6 - Physiological Optics > Final Review > Flashcards

Final Review Flashcards

1
Q

The peripheral cornea provides how much of the optical power of they eye?

A

2/3

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2
Q

What makes the corneal epithelium transparent?

A

Cells have a homogenous index of refraction
Cells are void of opacities and pigments
Cells are packed tightly with no extracellular fluid

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3
Q

What makes the corneal stroma transparent?

A

Organized lamellae of equal spacing at less than 1/2 the wavelength of light

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4
Q

Corneal thickness is about __ larger than what appears through a pachymeter.

A

1/3rd

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5
Q

Pachymetry requires knowledge of what two things?

A

Corneal refractive index

Radius of anterior corneal surface

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6
Q

What is the vergence equation?

A

L’ = L + F

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7
Q

Diverging light has a __ (+,-) vergence.

A

Negative

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8
Q

What does OCT stand for?

A

Optical coherence timography

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9
Q

What is the power equation?

A

F = (n2-n1) / r

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10
Q

What is the thickest layer of the tear film?

A

Middle aqueous layer (10 microns)

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11
Q

What is the thinnest layer of the tear film?

A

Bottom mucous layer (0.01-0.1 microns)

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12
Q

Why is Purkinje image 1 the brightest?

A

The largest index of refraction mismatch occurs between air and the tear film

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13
Q

What is the spacing of the corneal stromal lamellae?

A

About 60nm

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14
Q

What is the equivalent power formula?

A

Fe = F1 + F2 - [(d/n) F1 * F2]

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15
Q

With the equivalent power formula, if d increases, what happens?

A

Fe decreases

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16
Q

With the equivalent power formula, if n increases, what happens?

A

Fe increases

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17
Q

What is the formula for the vergence equation given index of refraction and distance?

A

n’/l’ = n’l + F

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18
Q

In pachymetry, does the image of the iris appear more anterior or posterior than it really is?

A

Anterior

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19
Q

OCT uses which properties of light?

A

Intensity
Wavelength
Polarization
Coherence

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20
Q

If you increase the depth of the anterior chamber, what happens to the overall power?

A

Decreases

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21
Q

Where do blue or green irides have pigment?

A

Melanin only in the epithelium

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22
Q

Image brightness is directly proportional to what?

A

Pupil area

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23
Q

Depth of focus is in the ___ plane.

A

Object

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24
Q

Depth of field is in the ___ plane.

A

Image

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25
Q

What is the blur equation?

A

B = P x K

pupil size) (refractive error

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26
Q

Large pupils give way to what?

A

Aberration

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27
Q

Small pupils cause what?

A

Diffraction

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28
Q

What limits supernormal vision?

A

Number and size of photoreceptors

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29
Q

Which is larger, the entrance pupil, or the exit pupil?

A

Entrance pupil

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30
Q

How far away from the real pupil is the image?

A

About 0.5mm in front

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31
Q

What forms the exit pupil?

A

The lens

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32
Q

Where is the exit pupil found?

A

In the vitreous

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33
Q

How far behind the real pupil is the exit pupil?

A

About 0.1mm

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34
Q

What is the overall magnitude of depth of field?

A

Between 1/2 and 1 diopter

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35
Q

What two things will increase depth of field?

A

Smaller pupil

Increasing ambient light

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36
Q

What kind of relationship exists between retinal blur and pupil diameter when in the presence of refractive error?

A

Linear relationship

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37
Q

Why does a pinhole lens make you see better?

A

Reduces all the aberrations

Doesn’t actually correct refractive error

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38
Q

What does LA-SD stand for?

A

Large pupil, only Aberration

Small pupil, only Diffraction

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39
Q

What is the point spread function equation?

A

r = 1.22λ f/d

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40
Q

What is the limit of resolution?

A

Reyleigh criterion

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41
Q

What does optical transfer function measure?

A

Loss in contrast of an image of a sinusoidal target

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42
Q

The higher the ___, the better the optics

A

MTF

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43
Q

The higher the __ __ the lower the MTF.

A

Spatial Frequency

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44
Q

What is RMS?

A

Variance of the aberration wave front

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45
Q

What is the Strehl Ratio?

A

Heye / Hdl

46
Q

The smaller the Strehl ratio, the ___ the optics.

A

Worse

47
Q

What is Zernicke Z20?

A

Defocus

48
Q

What is Zernicke Z2-2?

A

Astigmatism

49
Q

What is Z3-1?

A

Vertical coma

50
Q

What is Z31?

A

Horizontal coma

51
Q

Coma is common in what disease?

A

Keratoconus

52
Q

What is the most common Zernicke Polynomial?

A

Z20 - defocus

53
Q

What is Z40?

A

Spherical Aberration

54
Q

When does the eye have positive spherical aberration?

A

When relaxed

55
Q

When does the eye have negative spherical aberration?

A

When accommodating

56
Q

Cornea induces ___ spherical aberration.

A

Positive

57
Q

Which part of the eye induces negative spherical aberration?

A

Lens

58
Q

When is spherical aberration minimized?

A

At about 1.5D of accommodation

59
Q

What is TCA?

A

Difference in chromatic magnification across the retina

60
Q

What is the CDM equation?

A

Z x Kλ

61
Q

What is the equation for Kλ?

A

K_λ= K_L- K_S

62
Q

The average person has how much CDM?

A

0.8%

63
Q

Why is there chromatic aberration in the eye?

A

The watery medium in the eye has a refractive index that varies with wavelength

64
Q

What property of the photoreceptors helps mitigate the effects of chromatic aberrations in our vision?

A

The narrow sensitivity profile of the photoreceptors

65
Q

Which is refracted more, short or long wavelengths?

A

Short

66
Q

LCA is also known as:

A

Difference in Focus

67
Q

TCA is also known as:

A

Difference in Mag

68
Q

Off-Axis astigmatism is also known as:

A

Oblique astigmatism

69
Q

With off-axis astigmatism, what occurs with displacement?

A

It acts like a plus cyl with the axis perpendicular to that meridian

70
Q

Which plane is stronger, and therefore more anterior, tangential or sagittal?

A

Tangential

71
Q

To reduce astigmatism, where is the retina placed?

A

Between the tangential and sagittal planes

72
Q

Polarized light in the transmission axis appears what color?

A

Blue

73
Q

Polarized light perpendicular to the transmission axis appears to be what color?

A

Yellow

74
Q

In which condition is Hadinger’s brush not seen?

A

Macular edema

75
Q

In eccentric viewing, where is Hadinger’s brush seen?

A

Not in the center

76
Q

Under diffuse conditions, when will a shadow from inside the eye reach the retina?

A

Only if the opacity is the size of the pupil, or very close to the retina

77
Q

Which is the dimmest Purkinje image?

A

2

78
Q

Which is the larges Purkinje image?

A

3

79
Q

Which is the brightest Purkinje Image?

A

1

80
Q

Which is the only real Purkinje image?

A

4

81
Q

Which ocular surface reflects the most light?

A

Tear film/anterior cornea

82
Q

How much retinal mag is there per degree?

A

0.3mm per degree

83
Q

A 45 degree fundus photo will show how many mm?

A

13.5mm

84
Q

Which Purkinje Image is found 10-11mm behind the cornea?

A

3

85
Q

What is the optical axis?

A

Line connecting centers of curvature of the eye’s surfaces

86
Q

What is the visual axis?

A

Line connecting fovea and fixation that passes through the nodal point

87
Q

What is the pupillary axis?

A

Line passing through the center of the pupil and center of curvature of the cornea

88
Q

In the equation K = K’ -Fe, what does K’ represent?

A

Dioptric length of the eye

“Needs”

89
Q

In the equation K = K’ -Fe, what does K represent?

A

Refractive error

90
Q

In the equation K = K’ -Fe, what does Fe represent?

A

Dioptric power of the eye

“Has”

91
Q

1mm of elongation of the eye equates to about how many diopters of change?

A

3D

92
Q

Which eye model is best for studying the back vertex of the cornea?

A

Le Grand (4 surface)

93
Q

Which eye model is best for studying lens accommodation?

A

Gullstrand #2 (3 surface)

94
Q

Which eye model is best for studying refractive error?

A

Reduced eye

95
Q

Which eye model has a representation of the gradient index of the lens?

A

Gullstrand #1 or exact eye (6 surface)

96
Q

Which eye model is good for studying the optical power of the lens with changing indices?

A

Gullstrand #1 or exact eye (6 surface)

97
Q

What property do photoreceptors exhibit to catch light?

A

Total internal reflection

98
Q

Which wavelengths are best from producing an image of the retina?

A

Near-infrared light (700-1200)

99
Q

Light of what size will cause UV keratitis?

A

less than 0.3 microns

100
Q

Light of what size will cause cataracts?

A

Between 0.3 and 0.4 microns

101
Q

How is scatter reduced near the fovea?

A

Homogenous refractive index
Foveal neural tissue is pushed to the side
Avascular zone at the fovea

102
Q

How much light actually makes it to the retina?

A

42%

103
Q

37% of light is scattered and forms what?

A

A halo

104
Q

What amount of light is reflected or back-scattered by ocular tissues?

A

21%

105
Q

What does the SRK formula predict?

A

Power of IOL

106
Q

What is the power of the unaccommodated lens?

A

21.35D

107
Q

How “deep” is the unaccommodated lens?

A

6mm

108
Q

What is the power of the accommodated lens?

A

31.85D

109
Q

How “deep” is the accommodated lens?

A

10mm

110
Q

How does a gradient index lens reduce spherical aberration?

A

It is able to focus on one point, instead of multiple (like a uniform lens)

111
Q

What keeps the lens transparent?

A

Cell nuclei are near the equator
Close packing of cells reduces scatter at cell boundaries
Lens is avascular and w/o pigments, so absorbs little light

112
Q

Where is the index of refraction of the lens the greatest?

A

In the middle

Optics 6 - Physiological Optics (2 decks)

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