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Flashcards in Optics Deck (186):
0

Vergence

U+V=D

1

Prentice rule

PD=h*D

h (cm)
D diopter of lens power

2

Focal length

1/D=f

D= dist to object in m

3

Spherical equiv

Sphere+1/2cyl

4

Transverse mag

Image dist/obj dist

5

Axial mag

M transvrse^2

6

Simple magnifier

D/4

D= dioptic pwr of lens

7

Spectacle lens magnification

Mag=2% per diopter of pwr

8

Magnification of a telescope

Deyepiece/Dobjective

9

Refracting power of a spherical surface

D= n'-n/r

10

Power of a thin lens immersed in fluid

Dair = nIOL-nAIR
------- ------------
D aqu. nIOL-nAQU

11

REFLECTING power of a spherical mirror

Dreflecting= 2/r

r= radius of curvture

12

SRK formula

A-2.5(axl)-0.9K

13

In lens prob if image is + and is on other side of lens it is....

Real and inverted

14

In lens prob if image is - and forms on left side it is...

Virtual and upright

15

In schematic eye how far is K from nodal point?

5.5mm

16

In schematic eye how far is nodal point to the fovea?

17mm

17

In schematic eye, what is the axial length of the eye?

22.5 mm

18

In schematic eye, whats the diameter of the ON?

1.7 mm

19

Whats the refractive index of the cornea?

1.37

20

Whats the refractive index of air

1

21

Whats the refractive index of aqueous?

n=1.33

22

How much arc does the 20/20 E subtend?

5 min of arc

23

What's the radius of the corneal curvature in meters?

r=0.07m

24

How many min of arc does a 20/200 letter subtend?

50 min

25

How tall is a 20/20 letter?

9mm

26

What does laser stand for?

Light amplification by stimulated emission of radiation

27

what do you worry about w hyperopic shift?

orbital tumor

28

focal length?

f=1/D

29

What kind of mirror is a shaving mirror?

concave

30

reflecting power of a mirror

Drefl=1/f=2/r

31

when you use u+d=v and the answer is -, what does that mean in terms of real vs virtual etc

if its negative then its VIRTUAL AND UPRIGHT.
In a lens problem it to the left and in a mirror problem its to the right

32

how do you fix diplopia in anisometropic glasses?

put a "slab-off" prism on the more minus lens

33

whats placido disc keratometry?

looks like an ophthalmoscope projects rings onto the K gives a sense of irregular astigmatism

34

if you see scissoring on retinoscopy whats the dx?

kcn

35

what are the 5 steps in calculating rigid lens power?

1) chose a BC +0.50 steeper than low K value
2) convert rx to minus cyl form
3) drop the cyl
4) convert to zero vertex distance
5) subtract +0.50 from final value

36

how do you solve vertex distance questions?

1) understand that the glasses rx is not the refactive error of the eye!
2) find FP from the glasses and add the vertex dist- that's the true fp of the eye
3) find reciprocal of that dist to find real D error of eye

37

what's constructive interference?

two light waves from SAME LIGHT SOURCE are added together (laser?)

38

whats destructive interference?

two light waves from SAME LIGHT SOURCE cancel each other out

39

whats coherence?

the ability for two light waves or two parts of the same beam to produce interference (ie to interact w each other)

40

whats diffraction?

a light wave bends when it encounters an obstruction or apperture

41

what types of wavelengths diffract most?

long wavelengths

42

how does violet light behave in terms of refraction and diffraction

short wavelengths are refracted more and diffracted less

43

what phenomenon causes the sky to be blue?

scattering (blue is scattered, the rest of the wavelengths are diffracted)

44

whats the refractive index of the cornea?

1.376

45

a pt will feel comfortable using how much of their accommodative amplitude?

1/2

46

whats compound myopic astigmatism?

both images fall in vit

47

whats simple myopic astigmatism?

1 image falls on retina 1 falls on vitreous

48

whats mixed astigmatism?

one image in vit, one image behind retina

49

how do you make a CL fit tighter (2 options)

1) decr BC
2) incr diameter

50

what does angular magnification refer to?

magnification of SIMPLE MAGNIFIERS ie just divide by 4

51

how do you know what size aciol to put in?

take horizontal white to white and add 1

52

how can you help anisometropia in glasses without cl? hint: reduce everything

a) reduce central thickness of the lenses
b) reduce vertex distance- bring glasses closer to face
c) reduce the front surface power of the lens

53

what type of telescope is the operating microscope? kepler or galileo?

kepler (then theres a built in prism that flips the image)

54

whats the critical angle for total internal reflection of the K?

46 degrees

55

geometric optics deals w light as a...

ray

56

quantum opics deals w light as a...

photon

57

physical optics deals w light as a...

wave

58

whats the visble light spectrum (what nm to what nm?)

400-700nm

59

whats infrared spectrum what wavelength?

>700 (longer than red)

60

what wavelength is ultraviolet?

<160 (much shorter than violet)

61

whats interference?

when 2 rays of light are brought togther

62

whats destructive interference?

when 2 waves brought together and the intensity is minimized

63

what does coherence mean?

the ability of 2 light rays to make interfernce

64

in what direction are sunglasses polarized?

vertival slats, so any horizontal waves are blocked (light reflected off water is mostly horizontal)

65

what type of wavelength diffracts (ability to bend around edges) more?

longer wavelengths (like red)
think long stretch Armstrong bending around corner

66

whats brewsters angle?

the angle at which only 1 part of light that is polarized can be completely transmitted

67

when/how does scattering occur?

when light hits an irregularity in its path, it scatters

68

what are K edema, tindall effect and halos real life examples of?

scattering of light

69

whats the unit of photometry (light in units based on the response of the eye?)

candela

70

whats luminence?

amount of light emited by a surface measured in APOSTILLBS. real world example is GVF

71

whats the wavelength of yag and what spectrum is it in?

1064- infrared

72

whats the wavelength of argon green

514

73

do convex mirror act like + or - lenses?

minus

74

do concave mirrors act like + or - lenses?

+

75

whats the circle of least confusion

it represents the best overall focus of a spherocylindrical lens

76

what the conoid of sturm?

the complicated geometric envelope of light rays emanating from a spherocylindrical lens. The middle of it is the circle of least confusion

77

if a Maddox rod is held horizontally in front of you, how do you see the line?

vertical red line

78

why does nighttime exacerbate myopia?

bc pupil is big, light comes through all parts of cornea and causes spherical aberration (light from the steeply curved part of K gets focused anteriorly in the vitreous)

79

what test uses chromatic aberration?

duochrome (blue falls in vit, red falls behind retina)

80

whats the optical axis of the eye?

the line that best approximates light passing thru K, puil, lens and fovea

81

whats the pupillary axis?

imaginary line passing through K and exact center of pupil

82

whats the visual axis?

line between target and fovea

83

how does pupil size affect depth of focus?

smaller pupil gives better depth of focus

84

what is the diameter of the pinhole?

1.2mm

85

using a PH sc is only good for what refractive errors?

-5 to +5

86

how tall is a 20/20 E?

8mm

87

how is amplitude of accommodation expressed?

in D

88

how is range of accommodation expressed?

in mm

89

whats "emmitropization" of the eye?

the phenomenon that as a kid's eye grows, it doesn't become hugely myopic! the K actually sheds power so that the eye remains emmetropic

90

during retinoscopy for astigmatism, how do you know if you found the axis?

the reflex appears narrowest

91

whats the ideal add segment for hyperopes?

round top- decr image displacement but incr jump

92

whats the ideal bifocal seg for myopes?

flat top- decr jump and displace

93

how do you use press-on prisms

in one direction in 1 eye or you can out it the opposite direction in the other eye

94

whats the best way to correct for prismatic effect of anisometropia?

slab-off prism (aka bicentric grinding)

95

how do scl change the ability to accomodate

myopes have less ability to accommodate
hyperopes have more ability to accomodate

96

what type of cornea gets high BC?

flat K

97

How do you create a looser fit with a scl?

1) make BC flatter (incr BC #)
2) Decr the diameter (less of a suction cup)
3) decr the saggital depth

98

where do you measure white to white?

across horizontal cornea

99

how close to accurate does an iol with power <25D have to be?

within 0.4D

100

whats 2 example of a diffractive multifocal iol and how does it work?

reSTOR and technis multifocal IOL
back surface is like Fresnel prisms

101

IOL 25-30 diopters how close to accurate does it have to be?

0.5D

102

IOL >30D how close to accurate does it have to be?

within 1 diopter!!
so if you have a supershort eye youre screwed

103

whats the Q factor of the human cornea (the difference between central and peripheral K)

-0.26

104

whats the definition of angle kappa in optics terms?

the difference between the visual axis and the pupillary axis

105

whats the mag of the eye when using a direct?

15x (60/4)

106

what part of the slit lamp is made of an astronomical telescope?

the eyepiece (theres a prism that flips the image to upright)

107

what part of the slitlamp is a Galilean telescope?

the mag fxn (knob or flip thingy)

108

how does the image of the retina appear with a contact lens (tucker style)

minified upright

109

whats the diameter of the tonometer?

3.06mm

110

how does specular microscopy work?

its a reflection of the interface of the endothelium and the aqueous

111

how does a keratometer work? what does it measure?

it measures REFLECTING power (and infers refracting power)

112

what does placido disc measure

K topography (steepness only)

113

whats the A scan measure

TIME it takes for the sound wave to bounce back (looks like series of spikes) can be used to measure EOM thickness in TED

114

How does the laser inferometer work?

projects 2 light beam through dense cataract to macula, pt tries to discern 2 light beams

115

whats a brightness acuity tester?

looks like a small GVF dome, tests pt with cataract by glaring them w a dome of light

116

whats the WHO definition of legally blind

1) BCVA better eye of 20/200
or
2) field in better eye 20 degrees or less

117

how do blind pple deal w scotomas?

perceptual completion- the brain fills in missing parts of image

118

a pt with a scotoma is able to utilize an eccentric point of the retina for fixation, whats that called in optics terms?

preferred retinal locus

119

at what dist and w what chart is Va tested in low vision pple?

10 ft
ETDRS chart (has more low vision lines)

120

how do you determine add for a blind person? (kestenbaum rule)

take the inverse of the Va (ex 400/20 = 20)

121

what should you incorporate into glasses for super blind pple?

BI prism to bring eyes in

122

whos not a good candidate for handheld magnifier?

parkinsons, RA,

123

whats a stand magnifier?

a bulky thing you plop down on top of your newspaper

124

how should pple w low vision set up lamps in their house?

most illumination with least glare possible

125

How will a thick lens change the dioptric pwr of a lens?

will reduce the power

126

how much angular mag will be created if the image is virtual?

none

127

how do you calculate the K for a post-lasik pt if no historical data- do hard pmma lens refraction?

K= BC + Rcl - Rbare

K= K power
B= BC of hard PMMA ie the K
Rcl- refraction w cl on
Rbare= refraction with CL off

128

how do you calculate the K for a post-lasik pt if no historical data- do hard pmma lens refraction?

K= BC + power cl+ Rcl - Rbare

K= K power
B= BC of hard PMMA ie the K
Rcl- refraction w cl on
Rbare= refraction with CL off

129

who inserted the first IOL (in 1949)

Ridley

130

how can hard CL damage the K?

causes central epithelial edema

131

what can SCL cause on the k?

micropannus

132

diffraction sets a limit on visual acuity when the pupil is less than what size?

2.5mm

133

whats the wetting angle of a cl?

the degree to which water beads on the surface

134

0.13 meters = how many mm?

130mm

135

given lens +2, how do you find focal length?

d=1/f therefore f= 1/d
1/2
0.5m

136

how many decimal points do you move over for meter to centimeter?

2!!!!

137

how many decimal points do you move over for conversion from meter to millimeter?

3!!!!

138

if u+v+d if the answer is - then what does the image formed look like, and where does it fall in a lens problem vs a mirror problem?

if the answer is (-) then its virtual and upright!
in a lens question it goes to the left of the lens
in a mirror problem it goes to the right of the mirror

139

an angle of 20 dgrees corresponds to how many PD?

40
Double the angle (unless its >20)

140

an angle of 45 degrees corresponds to how many PD?

100

141

in a pt with 20/100 vision can you use a +/- 0.25 D Jackson cross?

no! too weak
must use a 0.75 or 1D Jackson cross

142

how do you make a Jackson cross cylinder?

the sph equiv of the rx = 0

143

if given BC in RGP problem, for every 0.05mm difference between the K reading and the BC you should do what?

0.25D/0.05mm
if flatter add plus
if steeper add minus

144

each clock hour is how many degrees in astigmatism?

30 degrees

145

how do you calculate post-op lasik K given pre-op refraction and Ks?

0.8 * starting refraction
then take that number and subtract from the avg starting K

146

indirect ophthalmoscop works like what type of telescope?

kepler (+20 lens of held lens and +60 lens of eye)

147

using a direct ophthalmoscope on a +10 hyperope, whats the mag?

acts like +50 mag (less condensing bc hyperopic) is 12.5

148

what type of telescope is the fundus camera?

kepler (the camera is plus lens and the eye works as the other plus lens)

149

if pt has a small pupil what things you can change on the indirect?

1) move your eyepieces further apart (decreases the EFFECTIVE pupillary distance)
2) bring triangular mirror closer to YOU
3) increase the distance between you and the pt

150

when prescribing high + add, what else do you have to give pt in his glasses?

give BI prism if add is >+4
give 2 PD greater than the reading add
ex: giving +8D add you should also give 10PD BI prism in each eye

151

how can you improve low vision in a pt w homonomous hemianopsia

give them prisms with the base toward the hemianopsia

152

whats 1/1.5? (multiply top and bottom by 2 = 2/3)

0.66

153

whats 0.5/1.5 (multiply top and bottom by 2= 1/3)

0.33

154

how do you calculate the power of piggyback lens?

hyperopia- 1.5*refractive error
myopia- 1*refractive error

155

whats the most vertical phoria that can be tolerated by anyone?

2 PD

156

What type of scan is best for measuring choroidal melanoma height?

a scan

157

whats the term that means the most amount of hyperopia and eye can take wo blurring the image?

manifest hyperopia

158

whats the term for the minimum hyperopic correction needed to see clearly?

absolute hyperopia

159

whats the term for cycloplegic hyperopia-manifest hyperopia?

latent hyperopia

160

whats spatial coherence?

when 2 parts of the same wave can produce interference

161

whats temporal coherence?

when 1 beam of light produces interference with itself

162

whats the definition of power in phaco?

the length that the phaco tip can travel relative to overall length

163

whats cavitation in phaco

when the phaco tip forms bubbles which breaks down lens

164

whats load in phaco?

the amount of lens in contact w the phaco tip

165

what 2/3?

0.66

166

whats 1/5

0.2

167

whats 1/6

0.16

168

whats 1/7

0.14

169

whats 1/8

0.12

170

whats 1/9

0.11

171

whats 1/15

0.066

172

how could you see polarized light?

wear polarized glasses and look at blue background (ie sky)

173

you give a pt more cyl than hes used to, what can you do to help him adjust?

1) turn axis more toward 90/180
2) decrease vertex distance
3) grid cyl onto back of lenses
4) decrease power of the cyl

174

how does giving a child w XT myopic glasses help?

makes the eye more hyperopic (image falls behind retina) they have to accommodate/converge/bring eye in

175

how many D of accommodation do you lose every 4 years?

1D

176

in HCL questions if given radius of K how to adjust?

for every 0.05mm adjust by 0.25D

177

which is the best iol formula for long eyes?

srk/t

178

which is the best iol formula for short eyes?

hofferQ

179

SPK at 3 and 9 o clock indicates tight fitting XXX cl

RGP

180

how will a spherical lens focus incoming light rays?

blur circle

181

amplitude of accommodation is what?

near point (D) - far point (D) IT IS NOT THE NEAR POINT

182

If you mess up axial length, which types of eyes are more effected?

short eyes

183

lensmeter works based on what principle?

badal principle

184

when a lens is submerged in water what happens to power?

becomes less powerful. careful if its half in air vs totally in water

185

what should be the power of the trifocal portion of glasses?

1/2 the add