Block 10 Flashcards
1
Q
T/F an optical system will alter the properties of light striking it in a predictable way
A
True
2
Q
Image Vergence:
A
Object vergence + Power
3
Q
- vergence
A
Diverging light
4
Q
+ vergence
A
Converging light
5
Q
What makes a real image
A
Exiting light with a positive vergence
6
Q
What makes a virtual image
A
Exiting light with a negative vergence
7
Q
What makes a real object
A
Incident light with a negative vergence
8
Q
What makes a virtual object
A
Incident light with a positive vergence
9
Q
What is paraxial approximation
A
Incident rays are close to the optical axis, which yields point images for point objects
10
Q
What is the optical axis
A
A line joining the centers of curvatures of the 2 surfaces of a lens
It passes through the lens at the optical center
11
Q
What is the axis of rotation
A
The axis perpendicular to the muscle plane around which the eye rotates when acted on
12
Q
What is lens effectivity
A
Change in vergence of light that occurs at different points along its path
13
Q
What are marginal rays
A
Rays on the periphery, far from the optical axis
14
Q
What are paraxial rays
A
Rays in close proximity to the optical axis
15
Q
What is an aperture stop
A
A physical entity that limits the amount of light passing through an optical system
16
Q
What is a field stop
A
The field stop limits the size of the object that can be imaged
17
Q
What is the depth of focus
A
The interval surrounding the retina in which an eye sees an object in focus
18
Q
What is the depth of field
A
The interval surrounding the fixation plane in which an object can reside and still be in focus
19
Q
An increase in aperture size leads to this
2 things
A
Decreased depth of field
Decreased depth of focus
20
Q
What are monochromatic aberrations
A
Wavelength independent aberrations
21
Q
What are some monochromatic aberrations that distort image quality
A
Spherical
Coma
Radial astigmatism
22
Q
What are some monochromatic aberrations that deform the image plane
A
Curvature of field
Distortion
23
Q
What are chromatic aberrations
A
Longitudinal
Transverse
24
Q
What is the basis for spherical aberration
A
Paraxial approximation is not always valid
25
What is longitudinal SA
Length of blur circle
26
What is lateral SA
Area size of blur circle
27
An increase in pupil size leads to _______
A decrease in image quality due to increased aberrations
28
What causes longitudinal SA
Marginal rays focus to a different location compared to paraxial rays
29
That causes coma
Magnification is varied as the height of incident rays above the axis is varied
30
What is coma found in
Off axis point sources
31
What 2 aberrations are irrelevant to ophthalmic optics
Spherical aberration
| Coma
32
What are high powered lenses needed for?
Necessary to compensate for spherical aberration by using aspheric lenses
33
T/F the eye rotates behind a lens to sample different areas
True
34
What are the 2 factors that influence the effective power o a lens
1. Increase in vertex distance for peripheral viewing causing a positive shit in effective power
2. Light rays strike at an oblique angle and induce astigmatism and spherical error
35
Spherical error combines ______
Field curvature
36
Cylindrical error combines ___
OA
37
What is OA due to
Rays hitting the lens obliquely causing the power to be altered by this tilt of the lens
38
What is the result of OA
A flat object plane yields an asymmetrically warped image plane
39
As the eye rotates toward the periphery, the tangential and sagittal planes move further from this
Far point sphere
40
What is tangential power
The power along the tangential Meridian in the periphery of the lens
41
What is sagittal power
The power along the sagittal meridian in the periphery of the lens
42
What is the curvature of field?
It relates to OA when there is a different warping along 2 principle axis
43
What is a petzval surface
Image surface created by a system with no OA, it is still warped due to curvature of field
44
Curvature of field is present in a lens system whenever _____
The petzval surface does not correspond to the far point sphere of the eye
45
What is a point focal lens
A lens corrected completely for OA, curvature of field is uncorrected
46
What is Percival form lens
A lens corrected for curvature of field
| OA is uncorrected
47
What causes distortion
Magnification of a point object depends on the objects distance from the optical axis
48
Distortion does NOT cause these 2 things
Blur and poor resolution
49
When is distortion a problem
In high powered lenses
50
What are the 2 types of distortion
Pincushion and barrel
51
What aberrations are most important for lens designers
1. OA
2. Curvature of Filed
3. Distortion
52
What is refractive index
It describes how much a given material will slow down and change the direction of a ray of light that passes through it
53
The higher the index, the ____ the lens can be and produce the ____ power
Thinner
| Same
54
What is LCA
An on axis aberration that occurs when different wavelengths are focused at different distances from the lens
55
What is TCA
An off axis aberration that occurs when different wavelengths are focuses at different points in the same focal plane
56
What test is used for chromatic aberrations
Red-Green Spherical test
57
What is chromatic dispersion
It quantifies the amount of chromatic aberration of a lens material
58
The lower the chromatic dispersion, the higher/lower the chromatic aberration
Lower
59
Is TCA or LCA more harmful to vision
TCA
60
Does TCA affect peripheral or central vision
Peripheral
61
What is Abbe number (v)
It quantifies the amount of chromatic aberration of a lens material
62
The higher the Abbe number, the higher/lower chromatic aberration
Lower
63
What is Abbe number the reciprocal of
Chromatic dispersive power
64
LCA unit
Diopter
65
LCA equation
LCA+ F/v
66
What is TCA unit
Prism Diopter
67
What is TCA equation
TCA: dF/v
68
TCA increases or decreases as you move to the periphery
Increases
69
Light incident on a lens has what fates
Transmission
Absorption
Reflection
70
Transmission+ absorption+ reflection:
100%
71
When light passes through a lens s it ______ on both surfaces and ______ by the les material
Reflected
| Absorbed
72
What is transmittance
The amount of light energy that gets through an optical system
73
How can light be lost when it hits a lens
Reflected
| Absorbed
74
What is fresnels law
It species the amount f light reflected from a surface
75
Look at equations from lecture 6
There are equations and conversions and some examples throughout
76
What is transmittance factor
The fraction of light transmitted per unit length of solid tin tied material
77
Substances with specific gravity greater than 1 will
Sink
78
Substances with specific gravity less that 1 will
Float
79
Light passing through a plus lens
Converges
80
Light passing through a minus lens
Converges
81
T/F rays of light entering a prism always bend around the base of a prism
True
82
T/F the image or object being viewed though a prism always shifts toward the apex
True
83
What is SSRI
A spherical lens with 2 spherical refracting surfaces
84
Concave lenses converge or diverge
Diverge
85
Convex lenses converge or diverge
Diverge
86
TF when a lens is tilted about the optical center the vertex distance changes
False, it does not change
87
What is pantoscopic tilt
Rotation of lens around the 180 meridian
88
What is faceform tilt
Rotation of a lens about the 90 meridian
89
What affect does rotating a lens have
Induces minus cylinder
90
For single vision lenses you need to make sure the optical axis of the lens passes through what?
The center of rotation
91
For every 2 degrees of pantoscopic you need to move the optical center how much?
1 mm lower
92
What are 4 ways the base curve can be maniplulated
1. Thickness and weight
2. Peripheral lens aberrations
3. Cosmetic considerations
4. Image size and magnification
93
Plano-convex and Plano-concave
One surface is flat the other is curved
94
Biconvex and biconcave
Both surfaces are curved
95
Equiconvex and equiconcave les
Half the total power is due to the front surface and half is due to the back surface
96
Meniscus
Convex front
| Concave back
97
Plano cylinder
One flat
| One cylinder surface
98
Toric
One toric surface
| 1 spherical surface
99
Base curve refers to what
The front sphere power
100
What is spherical equivalent
The sum of the spherical component and half the cylinder component of a lens
101
You want the base curve to be as close to what as possible
+6.00
102
What is vogels law for plus lens
Add the sphere power or spherical equivalent to +6.00
103
What is vogels law for minus lens
Add half the sphere power of spherical equivalent to +6.00
104
What vertex depth
The distance between the posterior pole of the lens and the perpendicular plane containing the posterior edge of lens
105
What is lens bulge
The distance between the anterior pole of the lens and the plane containing anterior edge of the lens
106
What is plane height
The height of the lens when laid down on a flat surface
107
What is a stigmatic system
A point source produces a point image
108
What is an astigmatic system
The power is different along different meridians
109
What is the location of the vertical focal line determine by
The power in the horizontal meridian of the lens
110
What is the horizontal focal line of a lens determined by
The power in the vertical meridian of a lens
111
In a cylindrical lens what is the axis meridian
The direction parallel to the axis of the cylinder
112
In a cylindrical lens what is the power meridian
The direction perpendicular to the axis meridian
113
What is the fitting triangle
When the frame is on a patients face it should touch junction of each ear
And the bridge of the nose
114
How do check that a lens is Co-planar
Check for misalignment from ABOVE
| Nose bridge will either be pushed forward or backward while lens is in correct tilt
115
What is lens X-in and how is it checked
The lens is twisted where eye wires meet at the bridge
Checked from above
116
What is skewed bridge/eyewires?
| How is it checked
Lenses are rotated inward or outward around the bridge
Checked straight on
117
How is face form checked for
From above
118
How do you check fro pantoscopic tilt
From the side
119
How do you check for parallel temples
From the sides
120
How do you check fro open temple angle
About for 90 degree angle
121
How do you check temple fold angle
From the back when the temples are closed
122
If the frames sit too low what should you do
Narrow the bridge
| Lower the vertical position of the pads
123
Is the eyelashes hit the frames what should you do
Narrow the pads to decrease faceform
124
If the frame touches the cheek, what should you do
Narrow the bridge or pads to raise the frame or increase the vertex distance
Reduce panto
125
If the frame slides down the face what should you do
Bring the temples in
Bend down the temple tips
Narrow the nosepads
126
If one lens is closer than the other what should you do?
Straighten the temples
127
If the segment height is too high?
Increase panto
Decrease vertex distance
Widen nose pads
Move pads up
128
If the segment is sitting too low
Reduce panto
Increase vertex distance
Narrow nosepads
Move pads down
129
If the fram is not level
Adjust the temple angle
130
If the right side of the fram is down
Move right temple down
131
If the right frame is up
Move the right temple up
132
What is lens thickness
It describes the edge or center thickness of a spectacle lens
133
Describe the thickness of a minus lens
Thicker on the sides
| Thinner in the center
134
Describe the thickness of a plus lens
Thicker in the center
| Thinner at the edge
135
When is delta t postive
For plus lenses
| Because the center thickness is greater than the edge
136
What are the 3 factors that affect lens thickness
Lens power
Lens diameter
Refractive index
137
Describe the isothickness curve of a spherical lens
Circular and centered on the optical center
138
Describe the isothickness curve of a cylindrical lens
Straight lines parallel to the axis
139
Describe the isothickness curve of a spherocylindrical lens
Circles, ellipses, hyperbolas, or straight lines
140
What is a fresnel prism
It's a prism
Less than 1 mm thick
Useful for short term treatment of binocular vision problems and evaluating whether prism can eliminate symptoms related to vertical imbalance
Adhere with water
141
When combining prisms, if they are going in the same direction you...
Add them like regular addition
142
When combining prisms, if they are perpendicular you....
Use Pythagorean theorum
143
Why is important to take vertical prism into account
If the amount is different, there is vertical imbalance
144
How do you find vertical imbalance
Find the difference in the amount of vertical prism in each eye
145
What is slab off prism
Inducing a vertical prismatic effect in the lower half of one lens to correct vertical imbalance
146
What is the usual effect of slab off prism
Induces BU in most minus lenses in the vertical meridian in order to offset excessive BD in the opposite lens
147
What is reverse slab off
It provides BD so it is always used in the most plus lens in the vertical meridian in order to offset excessive BU prism induced by the opposite lens
148
Where if the slab placed in flat top bifocal
In line with top of bifocal
149
Where is the slab in trifocals
Slab line should be at the bottom of intermediate portion
150
Where is the slab line in progressives
Slab line slightly above the near verification circle
151
How does slab off change the shape of minus lens
The lower half of the lens has more BU
152
What is dissimilar Segs
When you place the optical centers of the right and left segs at different positions
153
What is image jump
The sudden displacement of an image at the bifocal line
