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Optics > 1. Properties of light and visual function > Flashcards

1. Properties of light and visual function Flashcards

1
Q

optical radiation

A

lies between x-rays and mircowaves

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2
Q

how many subdivisions

A

seven
UVC, UVB, UVA, visible , IRA, IRB, IRC

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3
Q

wavelength for uvc

A

200-280nm

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4
Q

wavelength for uvb

A

280-315nm

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5
Q

wavelength for UVA

A

315-400nm

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6
Q

wavelength for visible

A

400-780nm

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7
Q

wavelength for IRA

A

780 - 1400

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8
Q

wavelength for IRB

A

1400-3000NM

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9
Q

wavelength for IRC

A

3000-10,000nm

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10
Q

shorter wavelength

A

greater energy

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11
Q

cornea and sclera absorb

A

very short UVB and UVC
very long IRB IRC

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12
Q

crystalline lens absorbs

A

UVA

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13
Q

what passes through

A

visible light and IRA
400 - 1,400nm

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14
Q

white loght

A

mixture of all visible light

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15
Q

colour and cone

A

Short = blue
Middle = green
Long = red

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16
Q

Blue, green and red wavelength length

A

blue 440
green 535
red 560

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17
Q

Green colour blind

A

deuteranopia

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18
Q

red colour blind

A

protanopia

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19
Q

blue colour blind

A

tritanopia

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20
Q

Clinical testing of colour vision

A

Farnsworth-Munsell FM hue 100
D-15
Ishihara - congenital red-green
Lanthony new colour test - paeds

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21
Q

Retinal photoreceptors are ALSO sensitive to

A

UVA (near UV)
350-400

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22
Q

UVA is normally absorbed by

A

the crystalline lens

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23
Q

retinal damage

A

350-441nm
UV to visible light

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24
Q

define fluorescence

A

property of a molecule to spontaneously emit light of a longer wavelenght when stimulated by light of a shorter wavelength

–> longer = less energy

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25
Q

Fluorescein

A

Excited by blue light (465-490)
Emits yellow (520-530)

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26
Q

fluorescein angiography assess

A

retinal and choroidal circulation

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27
Q

Describe FA

A

white light flash
goes thorugh blue excitation filter
blue light on fundus
most absorbed, some reflected unchange some is changed by fluorescence
seperate the reflected (unchanged + yellow)
camera only dtets the yellow (which is flureoscein leak from vessels)

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28
Q

indocyanine green

A

absorbs 805nm
emits 835nm (IR)

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29
Q

How does indocyanine green work

A

RPE doesn’t absorb ICG thf you see chorodial circulation

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30
Q

path of light

A

is always straight

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31
Q

wave motion

A

is a disturbance of energy passing through a medium
medium does not move but it vibrates at right angles to the direction of the wave

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32
Q

wavelength

A

distance between two symmetrical points

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33
Q

cycle

A

one complete oscillation (up and down)

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34
Q

white light

A

waves inphase = coherent

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35
Q

light waves out of phase

A

incoherent

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36
Q

two waves are in phase

A

CONSTRUCTIVE interference
resultant wave = summation of the two

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37
Q

two waves (of equal amplitude) byt out of phase by half cycle

A

DESTRUCTIVE intereference
cancel each out out

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38
Q

two waves out of step (less than half a cycle)

A

intermediate summation

39
Q

when does destructive interence occur

A

in the stroma
collagen bundle eliminate light with destructive interference

40
Q

define defraction

A

when a wave fronts encouters a narrow opening or the edge of an obstruction - the wave motion spread out on the far side of the obstruction

41
Q

fixation in babies

A

central, steady and maintained

42
Q

between 2-5months

A

visually directed reaching develops

43
Q

catford drum

A

white cylinder marked with blacks dots of increasing size
can measure from 6/6 to 2/60
when viewed at 60cm

44
Q

what are visually evoked potentials

A

electrical responses generated in the occiptal cortex by stimulation of the eye

45
Q

Optotype testing

A

for children between 18 and 24 months
match symbols

46
Q

Logmar

A

more prescise than snellen

47
Q

near vision

A

distance of 25-33cm

48
Q

potential visual acuity testing

A

used e.g. when cataract in the way
pin hile testing

49
Q

contrast sensitivity

A

ability to see low contrast objects, e.g. faces
lost in cataract, glaucoma, optic neuritis

50
Q

principle of contrast sensitvity measurement

A

sine wave grating, gradual transition between light and dark bands
narrower bands - higher spatial frequency

51
Q

how is contrast sensitivity measured clinically

A

Pelli robson chart

52
Q

glare testing

A

test VA in the prescence of a source of glare

53
Q

how is polarized light made

A

ordinary light encountering a polarizing substance ar agenet

54
Q

polarising agent

A

calcite crystals - only transmit light going in one plan

55
Q

how does a polarising agent affect light

A

reduces the radiant intensity but does not affect the spectral composition

56
Q

how can light also be polarised

A

reflected from a plane surface e.g. water if the angle of incidence if equal to the polarising angle for the substance

57
Q

birefringence

A

molecular structure which transmits light waves lying parallel to its structure but which selectively slows and therefore redirects light waves vibrating in a plane prependicular to its structure

58
Q

why do things that use biregringence have two refractice indcies

A

as they split inciden unpolairsed light into two polarised beams travelling in different directions

59
Q

define dichroism

A

causes light to be split up into different wavelengths
or
waves of different polorisations are absorbed by different amounts

60
Q

what effect does a dichroic substance have on light

A

completely blocks trasnmission of light waves not aligned with its structre by absoprtion
only one beam of polarised light emerges (much weaker)

61
Q

steroscopic vision

A

ability to fuse slightly dissimplar images procuding depth perception

62
Q

how should the retina be stimulated for stereoscopic vision

A

different parts of the retina that are WITHIN Panum’s fusional areas

63
Q

how is steroscopic vision graded

A

measured in seconds of arc
least horizontal disparity of the retinal image that evokes depth preception

64
Q

what is normal steroracuityu

A

60 seconds of arc or better

65
Q

what grading system measures steroacuity

A

Frisby stereotest range 600-15 seconds (minimum thf is 15 seconds)

66
Q

what is good steroacuity the product of

A

central single binocular vision

67
Q

what does steroacuity worse than 250 seconds suggest

A

amblyopia

68
Q

vectograph

A

two superimposed views presented in such a way that the light entering each eye is plan polaised
meaning that the light from one view being at right angles to that from the other
the compsoite pictreu must be view with polrising glasses

69
Q

Titmus / Writ fly test

A

graded sets of anumals and circles one of which is disparate and appears to stand foward
must be viewed be 40cm
range 3,000 to 40 seconds of arc

70
Q

Frisby test

A

three clear plastic plates of different thciknes
on each plate if four squares filled with random shapes
one scare has a ‘hidden’ circle
viewined at 40cm

71
Q

what seconds of arc can frisby give

A

340, 170 and 55 –> plates
by adjusting the viewing distance can give a range of 600 to 15 seconds

72
Q

TNO test

A

Random dot test using anaglyphs
480 to 15 seconds

73
Q

anaglyphs

A

sterogram in which two disparate views ae printed in red and green on a white backgroun
red green glasses are worn
through red fliteter only see green as balck and vice versa
two views may be fused to give a steroscopic effect

74
Q

Lang sterotest

A

fine vertical lines which are seen alternately by each eye when focused through bulit in cylindical lens elements
must be hled parallelt to the patient’s face to avoid uniocular clues

75
Q

what arcs does lang measure

A

1200 to 550 seconds of arc
uses preferntial looking for paeds

76
Q

define radiometry

A

quantifies radiant energey in all parts of the EMS

77
Q

define photometry

A

quanitfies only the raidant energy the evokes a visual reponse

78
Q

quantity of light emitted

A

radiant flux watt = joule / sec
luminous flux = lumen (lm)

79
Q

light emitted per unit solid angle

A

raidant intensity = watt / steradian
luminonous intensity candela = lm/sterraidna

80
Q

light refelcted or emitted by surgae in a ginve direction per solid angle per unit area

A

radiance = watt / steraidan/m2
luminance = candela / m2

81
Q

light per unit area incidence at surface

A

irradaince= watt /m2
illuminance = lux = lm/m2

82
Q

Emitted form light source
Intensity
Amount falling on a surface
Reflected

A

Radiant flux / luminous flux
radiant intenisty / luminois intensity
irradiance / illliuminance
radiance / luminance

83
Q

what is the peak photopic sensitivyt of the eye

A

555nm yellow / green

84
Q

1 wat of monochromati light

A

has the photometric equivalent of 685 lumens

85
Q

555nm has the

A

maxiumum luminous effencivty

86
Q

luminous efficienty is the

A

conversion factor specific for each wavelegnght determinded by the sensitivity of the eye to it
this is where radimetric and photmetric units are related

87
Q

what happens towards the end of the EMS in the eye

A

eye is progressivel y less sesnsitivt to wavelenghts towards each end of the EMS spectrum

88
Q

when does the conversion factor fall towards zero

A

outside the range of 400-700nm (visible light)

89
Q

STERADIAN

A

unit of solid angle (Resemblinga cone)

90
Q

define a steradia

A

anlge at the centre of a spehe which subtends an area onthe surgface of the spehe meauring the square of the radia

91
Q

defined perimetry

A

measures the light sensitivity of point on ht ertina by the ability of a patient to detect light stimuli of varuing intensity presented at corresponding points in the visual fields

92
Q

what is the standard backgroun luminance of most perimeters

A

31.5 apostilbs (asb)

93
Q

varaition of light intesnity in perimtery

A

between 0.8 to 10,000 asb

Optics (18 decks)

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