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Optics II block 5 > Axes And Angles > Flashcards

Axes And Angles Flashcards

1
Q

Any two optical systems are required to be aligned _______ to do efficient transmission

A

Coaxially

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2
Q

The human eye has 4 major optical surfaces, 1 aperture, and the retina, all of these are approximately ________

A

Equal

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3
Q

What are the axes of the eye

A
  1. Optical axis
  2. Pupillary axis
  3. Pupillary axis
  4. Line of sight
  5. Achromatic axis
  6. Fixation axis
  7. Keratometric axis
  8. Receptor axis
  9. Neural axis
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4
Q

The axis containing the centers of curvature of the eyes optical surfaces

A

Optical axis

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5
Q

The straight line along whihc a ray both enters and leaves the system

A

Optical axis

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6
Q

This axis a line of rotational symmetry

A

Optical axis

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7
Q

What are the decentered lights reflected off the surface of the eye

A

Purkinji images

-from 4 surfaces of decentered eye, and cant be aligned

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8
Q

Roatationally symmetric optical systems need one axis, which is

A

Optical axis

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9
Q

Not rationally symmetrical systems need _______

A

More axes

Like humans do

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10
Q

Some axes are dependent on

A

Idealized properties of the eye (nodal points, center of rotation)

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11
Q

This axis is used for all visual functions

A

Visual axis

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12
Q

The lone connecting the foveola and the fixation point passing through the nodal points

A

Visual axis (fovea achromatic axis)

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13
Q

Visual axis is called as ____________ as the rays passing through nodal points of the eye exhibit zero transverse chromatic aberration (TCA)

A

Foveal achromatic axis

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14
Q

The place of intersection of visual axis with the cornea is known as ____________, whihc is used in order to characterize cornea exactly

A

Ophthalmometric pole

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15
Q

The curvature of the cornea ________ as it moves away from the apex

A

Flattens

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16
Q

_______________ exactly locates the postion on the cornea

A

Ophthalmic pole

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17
Q

What is the ophthalmometric pole not influenced by?

A

Pupil fluctuations or accommodation

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18
Q

This axis is convenient reference point for visual functions

A

Visual axis

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19
Q

What does the visual axis not depend on

A

Pupil position

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20
Q

The line normal to the cornea passing through the center of the pupil

A

Pupillary axis

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21
Q

Which axis is important for treating eccentric fixation

A

Pupillary axis

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22
Q

This axis is used for aligning optical instruments to the eye

A

Pupillary axis

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23
Q

If the eye was a centered system and the pupil was also centered, the pupillary axis would lie along what axis

A

Optical

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24
Q

Adaptation to heterotropia

A

Eccentric fixation

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25
Q

Ray from fixation point that reaches the foveolar via center of the pupil

A

Line of sight

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26
Q

The path of foveal chief ray from fixation point

A

Line of sight

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27
Q

The paraxial optics, line of sight is called

A

Paraxial pupil ray

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28
Q

The postion at which the line of sight intersects the cornea is called the

A

Corneal sighting center

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29
Q

Where is the corneal sighting center in relation to the ophthalmometric pole

A

Superior

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30
Q

As useful reference when examining corneas that are undergoing refractive surgery

A

Line of sight axis

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31
Q

The line connecting the nodal point and the center of the pupil

A

Achromatic axis (foveal achromatic axis)

32
Q

The ray passing through the achromatic axis does not suffer from what

A

Any transverse chromatic aberration (TCA)

33
Q

Achromatic axis is similar to optical axis, but dependent on what

A

Pupil position

34
Q

The line passing through the fixation point and the center of rotation of the eye

A

Fixation axis

35
Q

This axis is the reference for measuring eye movements

A

Fixation axis

36
Q

This axis is just an approximation, depends on direction of rotation

A

Fixation axis

37
Q

The line passing through the fixation point and the center of curvature of anterior cornea

A

Keratometric axis

38
Q

This axis is used for alignment of corneal topography measurements

A

Keratometric axis

39
Q

The point at which the keratometric axis intercepts the cornea is sometimes called the what

A

Vertex normal

40
Q

__________ is the center videokeratographs showing corneal contour

A

Vertex normal

41
Q

Light from pupil has to be _______ to cone receptors

A

Coaxially

42
Q

Due to the fiber optics characteristics of the retinal photoreceptors, light arriving at the retinal plane along the photoreceptors axis will be ___________ and have a higher probability of being absorbed by the photopigment

A

Totally internally reflected

43
Q

Why are humans more sensitive to light passing through the section of the pupil that is coaxial with the receptor axis

A

Due to the fiber optics characteristics of the retinal photoreceptors, light arriving at the retinal plane along the photoreceptors axis will be totally internally reflected and have a higher probability of being absorbed by the photopigment.

The pupil appears to apodized

44
Q

Light brighter centrally than peripherally. Cones like signaled from center of pupil, not peripherally

A

Apodization

45
Q

The sampling density, and hence the spatial band-width of the neural image peaks at the _______ and declines monotonically with increasing eccentricity

A

Foveola

46
Q

Angle between the optical and visual axis

A

Angle alpha

47
Q

Angle formed at the first nodal point by the optical and visual axis of the eye

A

Alpha angle

48
Q

The angle between the visual axis and the optical axis (angle alpha) is considered to be ______ if the visual axis is on the _______ side of the optical axis in _________

A
  • positive
  • nasal side
  • object space
49
Q

The mean value of angle alpha is often taken to be about _________

A

+3-+5 degrees horizontally

50
Q

The visual axis is downwards relative to the optical axis by _____

A

2-3 degrees

51
Q

Angle between the pupillary axis and line of sight (LOS)

A

Angle lambda

52
Q

Angle formed at the first nodal point by the optical and visual axis of the eye

A

Angle lambda

53
Q

For most patients, the pupillary axis is _______ to the line of sight in ________. This is called a ______ angle

A

Temporal
Object space
Positive

54
Q

Angle lambda between the two eyes

A

Should be similar

55
Q

The angle lambda is important for diagnosis of

A
  • eccentric fixation (monocular testing)

- heterotropia (binocular testing) (Hirschberg)

56
Q

Angle between the pupillary axis and visual axis

A

Angle Kappa (k)

57
Q

For practical purposes, angle kappa is the same as _____

A

Angle lambda

58
Q

Angle between the visual axis and achromatic axis

A

Angle psi

59
Q

Both the visual axis and and achromatic axis both pass through the ____

A

Nodal points

60
Q

The mean psi angle was determined to be _____

A

+2.1 degrees

61
Q

Positive sign of angle psi indicates that visual axis is incline ______ to the achromatic axis in _____ space

A
  • nasally

- object

62
Q

Angle between the optical axis and he fixation

A

Angle gamma

63
Q

The angle gamma is within _____ of angle alpha for objects distances greater than 50cm

A

1%

64
Q

The images formed by reflection off the optical surfaces of the eye are referred to as

A

Purkinje images

65
Q

What is the brightest purkinje image

A

PI off the anterior cornea

66
Q

What Purkinje image is real and innerverted?

A

PIV from the posterior lens

67
Q

What are the major refracting surfaces what produce a purkinje image

A
  • anterior corneal surface
  • posterior corneal surface
  • anterior lens surface
  • posterior lens surface
68
Q

What are some things that purkinje images are important for

A
  • keratometry
  • corneal topography
  • alignment of optical instruments
69
Q

What are the steps for calculating the location of the Purkinje image I?

A
  1. Calculate the reflective power of the cornea
  2. Location of the reflected image
  3. Distance from the corneal surface
70
Q

Determine the location of the PI by treating the anterior corneal surface as a _______

A

Mirror

71
Q

Consider the light source to be at infinity and anterior cornea is 7.80mm, calculate PI

A

P=F=-2/r
F=-2/(.0078)
F=-256.41D

L’=L+F
L’=0-256.41D (light at infinity =0)
L’=-256.41

L’=-1/l
L’=-1/-256.41=.0038=3.90mm

72
Q

Alternate method for finding PI if light is at infinity

A

F=r/2
F=(7.8mm)/2
F=3.90mm

73
Q

A light is located 10.00cm anterior to the cornea of the eye. Assuming that the anterior surface of the cornea has a radius of 7.80mm, locate the first purkinje image

A

P=F=-2/r
-2/.00780=-256.41

L’=L+F
L’=-1/.1 + -256.41
L= -266.41

L’=-1/l
I’=-1/-266.41
I’=3.75mm

Purkinje image located 3.75mm to the right of the cornea

74
Q

Combining the refracting surface and mirror as a single system

A

Equivalent mirror

75
Q

Steps for finding the location of PIII image

A
  1. Calculate the reflective power of the cornea
  2. Treating the anterior lens as the object, find its image after refraction by the cornea
  3. Next, treat the anterior lens’ center of curvature as an object and find its image after refraction by the cornea

Optics II block 5 (11 decks)

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