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Optics 6 - Physiological Optics > Final Review > Flashcards

Final Review Flashcards

(112 cards)

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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
What is the blur equation?
B = P x K | pupil size) (refractive error
26
Large pupils give way to what?
Aberration
27
Small pupils cause what?
Diffraction
28
What limits supernormal vision?
Number and size of photoreceptors
29
Which is larger, the entrance pupil, or the exit pupil?
Entrance pupil
30
How far away from the real pupil is the image?
About 0.5mm in front
31
What forms the exit pupil?
The lens
32
Where is the exit pupil found?
In the vitreous
33
How far behind the real pupil is the exit pupil?
About 0.1mm
34
What is the overall magnitude of depth of field?
Between 1/2 and 1 diopter
35
What two things will increase depth of field?
Smaller pupil | Increasing ambient light
36
What kind of relationship exists between retinal blur and pupil diameter when in the presence of refractive error?
Linear relationship
37
Why does a pinhole lens make you see better?
Reduces all the aberrations | Doesn't actually correct refractive error
38
What does LA-SD stand for?
Large pupil, only Aberration | Small pupil, only Diffraction
39
What is the point spread function equation?
r = 1.22λ f/d
40
What is the limit of resolution?
Reyleigh criterion
41
What does optical transfer function measure?
Loss in contrast of an image of a sinusoidal target
42
The higher the ___, the better the optics
MTF
43
The higher the __ __ the lower the MTF.
Spatial Frequency
44
What is RMS?
Variance of the aberration wave front
45
What is the Strehl Ratio?
Heye / Hdl
46
The smaller the Strehl ratio, the ___ the optics.
Worse
47
What is Zernicke Z20?
Defocus
48
What is Zernicke Z2-2?
Astigmatism
49
What is Z3-1?
Vertical coma
50
What is Z31?
Horizontal coma
51
Coma is common in what disease?
Keratoconus
52
What is the most common Zernicke Polynomial?
Z20 - defocus
53
What is Z40?
Spherical Aberration
54
When does the eye have positive spherical aberration?
When relaxed
55
When does the eye have negative spherical aberration?
When accommodating
56
Cornea induces ___ spherical aberration.
Positive
57
Which part of the eye induces negative spherical aberration?
Lens
58
When is spherical aberration minimized?
At about 1.5D of accommodation
59
What is TCA?
Difference in chromatic magnification across the retina
60
What is the CDM equation?
Z x Kλ
61
What is the equation for Kλ?
K_λ= K_L- K_S
62
The average person has how much CDM?
0.8%
63
Why is there chromatic aberration in the eye?
The watery medium in the eye has a refractive index that varies with wavelength
64
What property of the photoreceptors helps mitigate the effects of chromatic aberrations in our vision?
The narrow sensitivity profile of the photoreceptors
65
Which is refracted more, short or long wavelengths?
Short
66
LCA is also known as:
Difference in Focus
67
TCA is also known as:
Difference in Mag
68
Off-Axis astigmatism is also known as:
Oblique astigmatism
69
With off-axis astigmatism, what occurs with displacement?
It acts like a plus cyl with the axis perpendicular to that meridian
70
Which plane is stronger, and therefore more anterior, tangential or sagittal?
Tangential
71
To reduce astigmatism, where is the retina placed?
Between the tangential and sagittal planes
72
Polarized light in the transmission axis appears what color?
Blue
73
Polarized light perpendicular to the transmission axis appears to be what color?
Yellow
74
In which condition is Hadinger's brush not seen?
Macular edema
75
In eccentric viewing, where is Hadinger's brush seen?
Not in the center
76
Under diffuse conditions, when will a shadow from inside the eye reach the retina?
Only if the opacity is the size of the pupil, or very close to the retina
77
Which is the dimmest Purkinje image?
2
78
Which is the larges Purkinje image?
3
79
Which is the brightest Purkinje Image?
1
80
Which is the only real Purkinje image?
4
81
Which ocular surface reflects the most light?
Tear film/anterior cornea
82
How much retinal mag is there per degree?
0.3mm per degree
83
A 45 degree fundus photo will show how many mm?
13.5mm
84
Which Purkinje Image is found 10-11mm behind the cornea?
3
85
What is the optical axis?
Line connecting centers of curvature of the eye's surfaces
86
What is the visual axis?
Line connecting fovea and fixation that passes through the nodal point
87
What is the pupillary axis?
Line passing through the center of the pupil and center of curvature of the cornea
88
In the equation K = K' -Fe, what does K' represent?
Dioptric length of the eye | "Needs"
89
In the equation K = K' -Fe, what does K represent?
Refractive error
90
In the equation K = K' -Fe, what does Fe represent?
Dioptric power of the eye | "Has"
91
1mm of elongation of the eye equates to about how many diopters of change?
3D
92
Which eye model is best for studying the back vertex of the cornea?
Le Grand (4 surface)
93
Which eye model is best for studying lens accommodation?
Gullstrand #2 (3 surface)
94
Which eye model is best for studying refractive error?
Reduced eye
95
Which eye model has a representation of the gradient index of the lens?
Gullstrand #1 or exact eye (6 surface)
96
Which eye model is good for studying the optical power of the lens with changing indices?
Gullstrand #1 or exact eye (6 surface)
97
What property do photoreceptors exhibit to catch light?
Total internal reflection
98
Which wavelengths are best from producing an image of the retina?
Near-infrared light (700-1200)
99
Light of what size will cause UV keratitis?
less than 0.3 microns
100
Light of what size will cause cataracts?
Between 0.3 and 0.4 microns
101
How is scatter reduced near the fovea?
Homogenous refractive index Foveal neural tissue is pushed to the side Avascular zone at the fovea
102
How much light actually makes it to the retina?
42%
103
37% of light is scattered and forms what?
A halo
104
What amount of light is reflected or back-scattered by ocular tissues?
21%
105
What does the SRK formula predict?
Power of IOL
106
What is the power of the unaccommodated lens?
21.35D
107
How "deep" is the unaccommodated lens?
6mm
108
What is the power of the accommodated lens?
31.85D
109
How "deep" is the accommodated lens?
10mm
110
How does a gradient index lens reduce spherical aberration?
It is able to focus on one point, instead of multiple (like a uniform lens)
111
What keeps the lens transparent?
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
Where is the index of refraction of the lens the greatest?
In the middle

Optics 6 - Physiological Optics (2 decks)

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