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Ophthalmic Optics > Block 10 > Flashcards

Block 10 Flashcards

1
Q

T/F an optical system will alter the properties of light striking it in a predictable way

A

True

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2
Q

Image Vergence:

A

Object vergence + Power

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3
Q
  • vergence
A

Diverging light

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4
Q

+ vergence

A

Converging light

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5
Q

What makes a real image

A

Exiting light with a positive vergence

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6
Q

What makes a virtual image

A

Exiting light with a negative vergence

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7
Q

What makes a real object

A

Incident light with a negative vergence

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8
Q

What makes a virtual object

A

Incident light with a positive vergence

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9
Q

What is paraxial approximation

A

Incident rays are close to the optical axis, which yields point images for point objects

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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

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11
Q

What is the axis of rotation

A

The axis perpendicular to the muscle plane around which the eye rotates when acted on

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12
Q

What is lens effectivity

A

Change in vergence of light that occurs at different points along its path

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13
Q

What are marginal rays

A

Rays on the periphery, far from the optical axis

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14
Q

What are paraxial rays

A

Rays in close proximity to the optical axis

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15
Q

What is an aperture stop

A

A physical entity that limits the amount of light passing through an optical system

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16
Q

What is a field stop

A

The field stop limits the size of the object that can be imaged

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17
Q

What is the depth of focus

A

The interval surrounding the retina in which an eye sees an object in focus

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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

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19
Q

An increase in aperture size leads to this

2 things

A

Decreased depth of field

Decreased depth of focus

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20
Q

What are monochromatic aberrations

A

Wavelength independent aberrations

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21
Q

What are some monochromatic aberrations that distort image quality

A

Spherical
Coma
Radial astigmatism

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22
Q

What are some monochromatic aberrations that deform the image plane

A

Curvature of field

Distortion

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23
Q

What are chromatic aberrations

A

Longitudinal

Transverse

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24
Q

What is the basis for spherical aberration

A

Paraxial approximation is not always valid

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25
Q

What is longitudinal SA

A

Length of blur circle

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26
Q

What is lateral SA

A

Area size of blur circle

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27
Q

An increase in pupil size leads to _______

A

A decrease in image quality due to increased aberrations

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28
Q

What causes longitudinal SA

A

Marginal rays focus to a different location compared to paraxial rays

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29
Q

That causes coma

A

Magnification is varied as the height of incident rays above the axis is varied

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30
Q

What is coma found in

A

Off axis point sources

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31
Q

What 2 aberrations are irrelevant to ophthalmic optics

A

Spherical aberration

Coma

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32
Q

What are high powered lenses needed for?

A

Necessary to compensate for spherical aberration by using aspheric lenses

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33
Q

T/F the eye rotates behind a lens to sample different areas

A

True

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34
Q

What are the 2 factors that influence the effective power o a lens

A
  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
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35
Q

Spherical error combines ______

A

Field curvature

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36
Q

Cylindrical error combines ___

A

OA

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37
Q

What is OA due to

A

Rays hitting the lens obliquely causing the power to be altered by this tilt of the lens

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38
Q

What is the result of OA

A

A flat object plane yields an asymmetrically warped image plane

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39
Q

As the eye rotates toward the periphery, the tangential and sagittal planes move further from this

A

Far point sphere

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40
Q

What is tangential power

A

The power along the tangential Meridian in the periphery of the lens

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41
Q

What is sagittal power

A

The power along the sagittal meridian in the periphery of the lens

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42
Q

What is the curvature of field?

A

It relates to OA when there is a different warping along 2 principle axis

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43
Q

What is a petzval surface

A

Image surface created by a system with no OA, it is still warped due to curvature of field

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44
Q

Curvature of field is present in a lens system whenever _____

A

The petzval surface does not correspond to the far point sphere of the eye

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45
Q

What is a point focal lens

A

A lens corrected completely for OA, curvature of field is uncorrected

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46
Q

What is Percival form lens

A

A lens corrected for curvature of field

OA is uncorrected

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47
Q

What causes distortion

A

Magnification of a point object depends on the objects distance from the optical axis

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48
Q

Distortion does NOT cause these 2 things

A

Blur and poor resolution

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49
Q

When is distortion a problem

A

In high powered lenses

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50
Q

What are the 2 types of distortion

A

Pincushion and barrel

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51
Q

What aberrations are most important for lens designers

A
  1. OA
  2. Curvature of Filed
  3. Distortion
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52
Q

What is refractive index

A

It describes how much a given material will slow down and change the direction of a ray of light that passes through it

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53
Q

The higher the index, the ____ the lens can be and produce the ____ power

A

Thinner

Same

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54
Q

What is LCA

A

An on axis aberration that occurs when different wavelengths are focused at different distances from the lens

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55
Q

What is TCA

A

An off axis aberration that occurs when different wavelengths are focuses at different points in the same focal plane

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56
Q

What test is used for chromatic aberrations

A

Red-Green Spherical test

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57
Q

What is chromatic dispersion

A

It quantifies the amount of chromatic aberration of a lens material

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58
Q

The lower the chromatic dispersion, the higher/lower the chromatic aberration

A

Lower

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59
Q

Is TCA or LCA more harmful to vision

A

TCA

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60
Q

Does TCA affect peripheral or central vision

A

Peripheral

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61
Q

What is Abbe number (v)

A

It quantifies the amount of chromatic aberration of a lens material

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62
Q

The higher the Abbe number, the higher/lower chromatic aberration

A

Lower

63
Q

What is Abbe number the reciprocal of

A

Chromatic dispersive power

64
Q

LCA unit

A

Diopter

65
Q

LCA equation

A

LCA+ F/v

66
Q

What is TCA unit

A

Prism Diopter

67
Q

What is TCA equation

A

TCA: dF/v

68
Q

TCA increases or decreases as you move to the periphery

A

Increases

69
Q

Light incident on a lens has what fates

A

Transmission
Absorption
Reflection

70
Q

Transmission+ absorption+ reflection:

A

100%

71
Q

When light passes through a lens s it ______ on both surfaces and ______ by the les material

A

Reflected

Absorbed

72
Q

What is transmittance

A

The amount of light energy that gets through an optical system

73
Q

How can light be lost when it hits a lens

A

Reflected

Absorbed

74
Q

What is fresnels law

A

It species the amount f light reflected from a surface

75
Q

Look at equations from lecture 6

A

There are equations and conversions and some examples throughout

76
Q

What is transmittance factor

A

The fraction of light transmitted per unit length of solid tin tied material

77
Q

Substances with specific gravity greater than 1 will

A

Sink

78
Q

Substances with specific gravity less that 1 will

A

Float

79
Q

Light passing through a plus lens

A

Converges

80
Q

Light passing through a minus lens

A

Converges

81
Q

T/F rays of light entering a prism always bend around the base of a prism

A

True

82
Q

T/F the image or object being viewed though a prism always shifts toward the apex

A

True

83
Q

What is SSRI

A

A spherical lens with 2 spherical refracting surfaces

84
Q

Concave lenses converge or diverge

A

Diverge

85
Q

Convex lenses converge or diverge

A

Diverge

86
Q

TF when a lens is tilted about the optical center the vertex distance changes

A

False, it does not change

87
Q

What is pantoscopic tilt

A

Rotation of lens around the 180 meridian

88
Q

What is faceform tilt

A

Rotation of a lens about the 90 meridian

89
Q

What affect does rotating a lens have

A

Induces minus cylinder

90
Q

For single vision lenses you need to make sure the optical axis of the lens passes through what?

A

The center of rotation

91
Q

For every 2 degrees of pantoscopic you need to move the optical center how much?

A

1 mm lower

92
Q

What are 4 ways the base curve can be maniplulated

A
  1. Thickness and weight
  2. Peripheral lens aberrations
  3. Cosmetic considerations
  4. Image size and magnification
93
Q

Plano-convex and Plano-concave

A

One surface is flat the other is curved

94
Q

Biconvex and biconcave

A

Both surfaces are curved

95
Q

Equiconvex and equiconcave les

A

Half the total power is due to the front surface and half is due to the back surface

96
Q

Meniscus

A

Convex front

Concave back

97
Q

Plano cylinder

A

One flat

One cylinder surface

98
Q

Toric

A

One toric surface

1 spherical surface

99
Q

Base curve refers to what

A

The front sphere power

100
Q

What is spherical equivalent

A

The sum of the spherical component and half the cylinder component of a lens

101
Q

You want the base curve to be as close to what as possible

A

+6.00

102
Q

What is vogels law for plus lens

A

Add the sphere power or spherical equivalent to +6.00

103
Q

What is vogels law for minus lens

A

Add half the sphere power of spherical equivalent to +6.00

104
Q

What vertex depth

A

The distance between the posterior pole of the lens and the perpendicular plane containing the posterior edge of lens

105
Q

What is lens bulge

A

The distance between the anterior pole of the lens and the plane containing anterior edge of the lens

106
Q

What is plane height

A

The height of the lens when laid down on a flat surface

107
Q

What is a stigmatic system

A

A point source produces a point image

108
Q

What is an astigmatic system

A

The power is different along different meridians

109
Q

What is the location of the vertical focal line determine by

A

The power in the horizontal meridian of the lens

110
Q

What is the horizontal focal line of a lens determined by

A

The power in the vertical meridian of a lens

111
Q

In a cylindrical lens what is the axis meridian

A

The direction parallel to the axis of the cylinder

112
Q

In a cylindrical lens what is the power meridian

A

The direction perpendicular to the axis meridian

113
Q

What is the fitting triangle

A

When the frame is on a patients face it should touch junction of each ear
And the bridge of the nose

114
Q

How do check that a lens is Co-planar

A

Check for misalignment from ABOVE

Nose bridge will either be pushed forward or backward while lens is in correct tilt

115
Q

What is lens X-in and how is it checked

A

The lens is twisted where eye wires meet at the bridge

Checked from above

116
Q

What is skewed bridge/eyewires?

How is it checked

A

Lenses are rotated inward or outward around the bridge

Checked straight on

117
Q

How is face form checked for

A

From above

118
Q

How do you check fro pantoscopic tilt

A

From the side

119
Q

How do you check for parallel temples

A

From the sides

120
Q

How do you check fro open temple angle

A

About for 90 degree angle

121
Q

How do you check temple fold angle

A

From the back when the temples are closed

122
Q

If the frames sit too low what should you do

A

Narrow the bridge

Lower the vertical position of the pads

123
Q

Is the eyelashes hit the frames what should you do

A

Narrow the pads to decrease faceform

124
Q

If the frame touches the cheek, what should you do

A

Narrow the bridge or pads to raise the frame or increase the vertex distance
Reduce panto

125
Q

If the frame slides down the face what should you do

A

Bring the temples in
Bend down the temple tips
Narrow the nosepads

126
Q

If one lens is closer than the other what should you do?

A

Straighten the temples

127
Q

If the segment height is too high?

A

Increase panto
Decrease vertex distance
Widen nose pads
Move pads up

128
Q

If the segment is sitting too low

A

Reduce panto
Increase vertex distance
Narrow nosepads
Move pads down

129
Q

If the fram is not level

A

Adjust the temple angle

130
Q

If the right side of the fram is down

A

Move right temple down

131
Q

If the right frame is up

A

Move the right temple up

132
Q

What is lens thickness

A

It describes the edge or center thickness of a spectacle lens

133
Q

Describe the thickness of a minus lens

A

Thicker on the sides

Thinner in the center

134
Q

Describe the thickness of a plus lens

A

Thicker in the center

Thinner at the edge

135
Q

When is delta t postive

A

For plus lenses

Because the center thickness is greater than the edge

136
Q

What are the 3 factors that affect lens thickness

A

Lens power
Lens diameter
Refractive index

137
Q

Describe the isothickness curve of a spherical lens

A

Circular and centered on the optical center

138
Q

Describe the isothickness curve of a cylindrical lens

A

Straight lines parallel to the axis

139
Q

Describe the isothickness curve of a spherocylindrical lens

A

Circles, ellipses, hyperbolas, or straight lines

140
Q

What is a fresnel prism

A

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
Q

When combining prisms, if they are going in the same direction you…

A

Add them like regular addition

142
Q

When combining prisms, if they are perpendicular you….

A

Use Pythagorean theorum

143
Q

Why is important to take vertical prism into account

A

If the amount is different, there is vertical imbalance

144
Q

How do you find vertical imbalance

A

Find the difference in the amount of vertical prism in each eye

145
Q

What is slab off prism

A

Inducing a vertical prismatic effect in the lower half of one lens to correct vertical imbalance

146
Q

What is the usual effect of slab off prism

A

Induces BU in most minus lenses in the vertical meridian in order to offset excessive BD in the opposite lens

147
Q

What is reverse slab off

A

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
Q

Where if the slab placed in flat top bifocal

A

In line with top of bifocal

149
Q

Where is the slab in trifocals

A

Slab line should be at the bottom of intermediate portion

150
Q

Where is the slab line in progressives

A

Slab line slightly above the near verification circle

151
Q

How does slab off change the shape of minus lens

A

The lower half of the lens has more BU

152
Q

What is dissimilar Segs

A

When you place the optical centers of the right and left segs at different positions

153
Q

What is image jump

A

The sudden displacement of an image at the bifocal line

Ophthalmic Optics (1 decks)

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