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Ophthalmic Optics Block 10 > Physical And Optical Chara Of Ophth Lenses > Flashcards

Physical And Optical Chara Of Ophth Lenses Flashcards

1
Q

Relating to the eye, this refers to the interval surrounding the retina in which an eye sees an object in focus

A

Depth of focus

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2
Q

Short focal length leads to _______ depth of field

A

Large

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3
Q

The interval surrounding the fixation plane in which an object can reside and still be in focus

A

Depth of field

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4
Q

An increase in aperture size and depth of field

A

Decreases depth of field and depth of focus

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5
Q

Create optical distortions in image quality or a deformation of the image plane

A

Aberrations

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6
Q

Two types of aberrations

A

Monochromatic and chromatic

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7
Q

Wavelength independent aberrations

A

Monochromatic aberrations

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8
Q

Monochromatic aberrations that distort image quality

A

Spherical
Coma
Radical astigmatism

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9
Q

Monochromatic aberrations that deform the image plane

A

Curvature of field

Distortion

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10
Q

Chromatic aberrations

A

Longitudinal

Transverse

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11
Q

An aberration that occurs when peripheral rays focus at different points on the optic axis than the parasail rays

A

Spherical aberrations

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12
Q

Length of a blur circle

A

Longitudinal SA

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13
Q

Area size of blue circle

A

Lateral SA

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14
Q

What is the basis for SA

A

Paraxial approximation is not always valid

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15
Q

Increase in pupil size leads to a _____ in quality of image due to _______ aberrations

A

Decrease

Increased

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16
Q

Point of focus of a beam of light is dependent on where the light stroked the optical system

A

Longitudinal SA

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17
Q

Marginal rays focus to a different location compared to parazial rays

A

Longitudinal SA

-a point object is no longer forming a point image (the image is blurred)

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18
Q

Results from the fact that mag is varied as the height of incident rays above the axis varied

A

Coma

  • asymmetric comet-shape patch
  • only in off-axis point sources
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19
Q

Relevance of SA and coma

A

Largely irrelevant to ophthalmic optics because the small pupil size only accepts paraxial rays
-very high powered lenses-necessary to compensate for spherical aberration by using aspheric lenses

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20
Q

Two factors that influence the effective power of a lens

A
  • Increase in vertex distance for peripheral viewing resulting in a positive shift in effective power for plus and minus lenses
  • light rays strike at an oblique angle inducing astigmatic and spherical error
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21
Q

Spherical error

A

Field curvature

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22
Q

Cylinder error

A

Oblique astigmatism

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23
Q

Other terms as oblique astigmatism

A

Radical astigmatism or marginal astigmatism

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24
Q

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

A

oblique astigmatism

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25
Q

What is the most important aberrations in lens design

A

OA

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26
Q

A flat object plane yields an asymmetrical warped image plane

A

OA

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27
Q

As the eye rotates towards the periphery, the tangential and Sagittarius planes move furthers from the far point sphere

A

OA

Teacup and saucer

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28
Q

The power along the tangential meridian in the periphery of a lens, the difference between this and Sagittal powers is the oblique astigmatism

A

Tangential power

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29
Q

The power along the sagittal meridian in the peripheral of a lens. The difference between this and tangential powers the OA

A

Sagittal power

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30
Q

Power error

A

Curvature of field

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31
Q

If for each point on that paper,we find the image point we will notice that the image points formed by all points on the paper do not lie on a plane. This means that image plane is warped, even for a lens that is not tilted. This would mean that the quality of an image on a flat screen decreases for larger distances

A

Curvature of field (power of error_

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32
Q

Related to OA when there is a different warping along two principal axis

A

Curvature of field

-stil have warping without OA

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33
Q

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

A

Petzval surface

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34
Q

Present in ophthalmic optics lens system whenever the petzval surface does not correspond to the far point sphere of the eye

A

Curvature of field

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35
Q

Lenses that have been corrected for OA, curvature of field, or both are corrected curve lenses

A

Corrected curve theory

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36
Q

A lens corrected completely for radial astigmatism, but curvature of field is incorrect yes

A

Point focal lens

37
Q

A lens corrected completely for curvature of field, OA uncorrected

A

Percival form lens

38
Q

Results from magnification of a point object depends on the objects distance from the optical axis. Straight line objects form straight line images only if the line passes through the optic axis, all other lines will be curved

A

Distortion

39
Q

How can distortion be minimized

A

Correctly placing stops

40
Q

What are the two types of distortion

A

Barrel and pincushion

41
Q

When is distortion a problem

A

For high powered lenses

42
Q

Which aberration is of the most concern to lens designers

A

OA

43
Q

Teacup and saucer image

A

OA

44
Q

How can OA be reduced

A

Picking the correct base curves

45
Q

Shows best base curve for eliminated OA

A

Tscherning ellipse

46
Q

If incorrect BC used in OA

A

Vision reduced in periphery

47
Q

Limitation of Tschrening ellipse

A

Upper limit is +7.50
Lower limit is -22.00D
Outside the limits-aspheric lenses

48
Q

An optical system (a lens) will alter the properties of light striking it in a predictable way

A

Vergence

49
Q

Measures the degree of converging or diverging of a light wave at a given point in space

A

Vergence

50
Q

Negative vergence

A

Diverging light

51
Q

Positive vergence

A

Converging light

52
Q

Image vergence equation

A

Object vergence + power

V=U+P

53
Q

Exiting light with a positive vergence

A

Real images

54
Q

Exiting light with a negative vergence

A

Virtual image

55
Q

Incident light with a negative vergence

A

Real object

56
Q

Incident light with a positive vergence

A

Virtual object

57
Q

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

A

Paraxial approximation

58
Q

The line joining the centers of curvatures of the two surfaces of a lens and passes through the lens at the optical center

A

Optical axis

59
Q

Optical axis is _________ to each surface, so light passing though the axis is undeviated

A

Perpendicular

60
Q

The axis perpendicular to the muscles plane around which the eye rotartes when acted on

A

Axis of rotation

61
Q

Change in vergence of light that occurs at different points along its path (related to vertex distance)
-two lenses have the same effective power if they form a real or virtual image of an object at the same point

A

Lens effectively

62
Q

Rays on the periphery, far from the optical axis

A

Marginal rays

63
Q

Rays in close proximity to the optical axis

A

Parazial rays

64
Q

Limits an optical systems field of view s

A

Stops

65
Q

Physical entity limits the amount of light passing into an optical system when viewing an object, could be an actual aperture, like in a camera, or another physical element, light the edge of a lens

A

Aperture stop

66
Q

This limits the size of the object that can be images by the system

A

Field stop

67
Q

Light waves travel through transparent media at different speeds

A

Refraction index

68
Q

The ratio of the spend of light in a vacuum (or air) to the speed of light in another medium

A

Refraction index

69
Q

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

A

Refraction index

70
Q

The higher the index, the ____a lens can be and produce the same power

A

Thinner
-a -8.00 with an index of refraction of 1.74 will always be thinner than a lens with an index of refraction of 1.586 with the same power

71
Q

Dependent on the wavelength leading to chromatic dispersion

A

Refraction

72
Q

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

A

Longitudinal chromatic aberration (LCA)

  • dioptric difference between red and blue powers
  • vary by location
  • refers to a lens as a whole
73
Q

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

A

Transverse chromatic aberrations (TCA)

  • blue light is deviated more than red light
  • vary by size
  • prism diopter
74
Q

Leaders the apprentice of color fringes

A

Chromatic aberrations

75
Q

Underlies the use of the red green spherical test in clinical refraction

A

Chromatic aberration

76
Q

Red and green in refraction

A

Discrepancies between red and green yield a more precise estimate of the refractive error of the ey than would a monochromatic stimulus

77
Q

Quantifies the amount of chromatic aberration of a lens material

A

Chromatic dispersion

78
Q

The lower the chromatic dispersion, the ______chromatic aberration present in the lens

A

Less

79
Q

Is lower or higher chromatic dispersion better

A

Lower

80
Q

Transverse chromatic aberration is more _____to vision

A

Harmful

  • results in different prismatic effects for different wavelengths
  • impacts peripheral viewing
81
Q

How to minimize CA when using materials with low Abbe number

A

Use shorter vertex distances
Monocular PD
Add sufficient panto

82
Q

Quantifies the amount of chromatic aberration of a lens material

A

Abbe number

83
Q

Higher the abbe number, the ____chromatic aberration present in the lenses

A

Less

84
Q

Is bigger or smaller abbe number better

A

Bigger

85
Q

Reciprocal of the chromatic dispersive power

A

Abbe number

86
Q

High index materials, have a ______ abbe number

A

Lower

-only use this is you value thin lenses over quality of image

87
Q

LCA equation

A

LCA=F/v

V=abbe value
F=lens power

88
Q

TCA equation

A

TCA=dF/v

V=abbe value
D=distance from optical center of the lens (cm)
F=lens power

89
Q

What is a good abbe number

A

40s into low 50s

Ophthalmic Optics Block 10 (4 decks)

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