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Optics 4 > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

How many curves are generally used for base curves?

A

4 to 6

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2
Q

What is the mold consisted of in a traditional lens?

A

Base Curve and Add Power

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3
Q

What part of the lens is grinded by the lab?

A

Back surface

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4
Q

What are traditional PROGRESSIVE lenses designed for?

A

Lensometer

Not the patient

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5
Q

What happens when you decrease the corridor?

A

Astigmatism will increase

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6
Q

Which age group look for fashion more than visibility?

A

18 to 34 yrs

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7
Q

Which frame has crystals in it?

A

Carbon fiber

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8
Q

Which type of frame do you insert cold lenses into?

A

Carbon fiber

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9
Q

What is Nylon made of?

A

Cellulose Acetate Propionate

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10
Q

Which frames are Hypoallergenic?

A 
Nylon
Stainless Steel
Titanium
Optyl
Polyamide
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11
Q

What frame do you use hot water for?

A

Nylon

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12
Q

Which do you not leave on your car dash? Why do you not leave it there?

A

Optyl

It will go to the default position

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13
Q

What specific safety frame do you not use acetone for?

A

Polycarbonate

It will turn into milky texture

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14
Q

What is a major metal allergy?

A

Nickel

Trical

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15
Q

If a pt. has excessive perspiration, what type of frames should you give to your pt.?

A 
Corrosion resistant
Aluminum
Titanium
Metal Alloys (Often)
Stainless Steel
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16
Q

What type screw mounting do you not do on Glass lenses?

A

Conventional screw mounting

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17
Q

What happens to the light speed when you go from Polycarbonate to Trivex?

A

Go faster

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18
Q

If you have a pt. with 3 BU. How many degrees will the lens be at?

A

1.71

3 x .57 = 1.71

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19
Q

What are 2 things prism should be displayed?

A

Quantify ANGLE OF DEVIATION IN DEGREES and

the AMOUNT OF DISPLACEMENT

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20
Q

How much prism power does a prism have if it displaces a ray 5cm. from a distance of .5m from the prism?

A

10 PD

5cm/.5m

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21
Q

A 20Δ BU will deviate a ray how far at 5m and in what direction?

A

100 cm

20 x 5

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22
Q

A prism deviates light 4 degrees. What is the power of the prism?

A

4 x 1.75 = 7.00

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23
Q 
Your patient has the following Rx:  		            
OD Plano - 7.00 x 090
OS -3.00 DS. 
3ΔBO 			 	  
On which lens should the prism be Rxed?
A

OS

OD = -7.00 +7.00 x 180
OS = -3.00 DS (not as thick)
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24
Q

Your patient has suffered a stroke and has a OD blind spot superior temporal. You want to prescribe prism to bring the non-seeing area into his seeing area by 30 degrees.

A

52.5 BU

30 x 1.75 = 52.5

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25
Q

What part of a minus lens is fixed?

A

Center

This is why the edges are variable

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26
Q

What happens when you decrease the refractive index?

A

Increased edge (minus) and center (plus)

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27
Q

Calculate the Lens Thickness
Given: F1 = +2.00, F2 = -8.00 and n = 1.5
lens dia. = 80 mm, and tC = 2 mm.

A

T = 11.6 mm

S = (Fh^2) ÷ 2000(n - 1)
s1 = -6(40^2) ÷ 2000(1.5 - 1) = 9.6mm + 2mm =
11.6 mm

Note: Every minus lens has a minimum thickness where you must add 2mm

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28
Q

When looking for Thickness of lens, what would occur if you increased the diameter?

A

The lens would get THICKER

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29
Q

What is the formula for Total Light Transmission?

A

TIT = L - (reflection + absorption)

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30
Q

What is the formula for Reflection?

A

R = (n’ - n)^2 ÷

(n’ + n)^2

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31
Q

How much light is transmitted by CR-39, assuming no absorption?

A

92.2%

R = (1.498-1)^2 ÷
(1.498 + 1)^2 = 4.0% (F1)

Then 96 would be the I, and since 4% was the reflected, it would be 96% x 4% = 3.8% reflected. 96% - 3.8% = 92.2%

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32
Q

In regards to absorption, if you add more layers, what would that do to the absorption?

A

Absorption will increase and light being refracted will decrease

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33
Q

What does Lambert’s law state?

A

Given an absorptive material such as a tinted lens, layers of equal thickness absorb equal % of light regardless of the intensity…

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34
Q

What is the formula for light transmitted after absorption?

A

Ix = Io x q^x

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35
Q

Find T of crown glass, n =1.523,assuming the q value = 0.8 / 2 mm and tc = 6mm

A

46.9%

F surface = 4.3%
95.7 (0.8^3) = 0.49

B surface =0.49 x 0.043 = 0.021

T= Ix - Rb
0.49 -0.021 = 0.469 or 46.9%

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36
Q

What is the short cut formula for Total light transmitted?

A

T = Io x (q^x)

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37
Q

What is the order of transmission for UV protection?

A

CR39 (dyed) > Polycarb > CR39 (not tinted) > Crown Glass

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38
Q

What part of the lens will have the least amount of tint?

A

Thickest part of the lens

Oxidates will go to the thickest part of the lens

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39
Q

How do you calculate what AR you need to use?

A

Square root the n of the lens you have.

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40
Q

True or False. Single layer AR will allow more wavelengths to pass through?

A

False. Only one wavelength will pass through

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41
Q

What makes the AR coating tough now a days?

A

Silica

42
Q

What is unique about teflon coating?

A

The increase the degree of water angle, thus beading off.

43
Q

What is a major drawback of modern AR coatings?

A

No UV protection

Use AR with transition (photochromics)

44
Q

Your pt. wants to know how much thinner will be the lenses, what do you do?

A

Current lens / New lens
Ex. 498/586 = 0.85 thick
15% thinner

45
Q

What is the benefit of Aspheric lens in plus lens?

A

Flatten at the EDGE

Note: Only on side

46
Q

What is the benefit of minus aspheric lenses?

A

Steepen at the edge of the lens

Note: Only on one side

47
Q

Which pts. have better optics plus or minus?

A

Plus

48
Q

What is the main feature of an Aspheric Lens?

A

Minimize off-center errors

49
Q

What are 3 things that ashperic lenses reduc

A

SAD

Spherical Abberation, Astigmatism and Distortion

50
Q

What are three main features of having flatter back curves?

A

Reduces corneal vertex distance, Minimize mag, and pts. eye appear normal in size

51
Q

When you need a base curve for a minus lens, what do you do?

A

Spherical equivilent and add 8

Note: For Plus lens you add 4 to the Rx.

52
Q

Where are Aspherics traditionally placed and where are Atorics placed now?

A

Aspherics = Front

Atorics = Back

53
Q

If your pt. shows high amount of cylinder, which type of lens would you fit them in?

A

Atoric

Note: They are limited both material and index

54
Q

How are Aspheric lenses denoted?

A

With Laser engraving. Marks are usually 17 mm from the center

55
Q

What is a good method for reducing edge thickness?

A

Roll and Polish

56
Q

What is one main disadvantage of an Aspheric lens?

A

Cannot compensate for all cylinder power

57
Q

What are 2 terms you don’t use when giving pts. recommendations of glasses?

A

Unbreakable and Shatter Proof

Note: There is no law where we must put pt.s in POLY or TRIVEX

58
Q

True or False. Edging, Coating and tinting a lens becomes a manufacturer is liable for the impact resistance of the lens?

A

True. IMPACT RESISTANCE ONLY

59
Q

What requirements must a dress lens pass?

A

Performance test

60
Q

Which lens fogs easily?

A

Crown Glass

61
Q

What type of tempering must be done for safety lens?

A

Heat tempering

62
Q

What is the best plastic with high optics?

A

Trivex

63
Q

The FDA will not approve of a lens that has a _______ in its lens?

A

Fracture

64
Q

What type of lenses must be tempered in either heat or a chemical bath?

A

Glass lenses

65
Q

When you put on a AR coat, how much protection does the coat provide for the lens?

A

14 times more

66
Q

What type of lens requires just the basic impact test?

A

Plastic

-3.0mm at the lens thinnest point

67
Q

How many lens are tested for each type of lens?

A

3 lenses are tested

68
Q

If you see a “+” on the lens, what does this mean?

A

High impact velocity test was conducted

69
Q

What will be the marker for a safety lens

A

z87-2

70
Q

When can you have diplopia with an aphakic eye?

A

The image will be 25% with the Normal eye

71
Q

What does Mp stand for?

A

Power Magnification

MP = 1 ÷ [1 - h(FV)]

72
Q

What does Ms stand for?

A

Shape factor

MS = 1 ÷ [1 - F1(tc ÷ n)]

73
Q

How do you calculate Mspec?

A

Mp x Ms = Mspec

74
Q

How do you calculate %Mspec?

A

(Mpsec - 1)x 100 = %

75
Q

What are the possible ways to alter Mspec for a plus lens?

A

Increase the index

Decrease Vertex, BC or Tc

76
Q

What are the possible ways you can decrease minification?

A

Increase BC or Tc

Decrease Index or vertex

77
Q

When you have a high plus or high minus, which way do you move the bevel?

A

Towards the front of the lens

78
Q

If you have a pt. with anisometropia, where do you move the bevel to?

A

The front

79
Q

When there axial ametropia, what does this mean?

A

The retinal image cannot fully fuse at the fovea due to length of the eye

80
Q

What would happen to the lens if there was no panto?

A

Sphere power would increase

81
Q

How do you find the tilt angle?

A

Measure in mm between 1 and 2, then double it to find the tilt angle

82
Q

How do you find the wrap angle?

A

measure in mm between 1 and 3 and double it to find the wrap angle in degrees

83
Q

What formula do yu use for calculating the new sphere?

A

S= S {1+(sino^2)/2n}

84
Q

How do you calculate the induced cylinder?

A

C = S’(tan a^2)

85
Q

When do you cancel vertical prisms?

A

When they are the same vertical base

86
Q

When do you cancel horizontal prism?

A

BI and BO

87
Q

What are the 2 factors in regards to prismatic effect when OC is decentered?

A

Cylinder power and Axis Orientation

88
Q

What is the formula for when you would like to Focal Power of a meridian in question?

A

F = Fs + Fc (sin0^2)

89
Q

You are checking your own glasses in the lensometer and find your right lens has unwanted prism. The prism reads 2.00 base 30. What vertical and horizontal values does this prism have?

A

OD 2 Base 30
V = P sin 0
H = P cos 0

V = 2 sin 30
=1 PD

H = 2 cos 30
= 1.73 PD

90
Q

What is the formula when you have base thickness of a prism?

A

P = 100g ( n - 1 ) / d

91
Q

What is the best setup for a pt. who requires little movement from distance to near?

A

Raising segment height

92
Q

When should you NOT preform slab off?

A

If the combined Prismatic effect is less than 1.5 PD

93
Q

Where do you normally grind on a slab off on a pair of lenses?

A

F1

94
Q

Which lens do you use a FT for?

A

Most minus

95
Q

OD -7.00 DS OS -4.50 DS Add +2.00
seg lines 5 mm below distance OCs (seg drop)
reading level 10 mm below distance OCs
Correct the vertical imbalance using dissimilar segment styles for each lens

A

Give the pt. OD FT and OS RS Ultex E

OD = 7 x 1 = 7BD
OS 4.5 x 1 = 4.5 BD
Vert. Imbalance = 2.5 BD OD
Dist. needed btwn seg OCs: 2.5 = 2.00 x 1.25 cm
Seg OC must be 12.5 mm + 5 below seg top
What BF segment OC = 17.5 mm below the top of the segment line?

96
Q 
Distance Rx -2.00D OU with +2.00 add
Frame size 50 mm with 18 mm DBL
Patient’s PD 64/60
Segment inset = ?
Total inset = ?
A

1) Calculate decentration (inset) Frame PD - Pt. PD = 68-64 or 4 mm. Move OC’s 2 mm in, each lens
2) Seg Inset Dist. PD - Near PD = 64-60/2 or… 2 mm in, each lens from dist. OC’s

3) Total Inset Frame PD - Near PD 68-60/2
4 mm in, each lens from GC

97
Q

What is the formula for Linear FOV?

A

FOV = [(d + 2.7) x (2h)] ÷ 2.7

98
Q

Calculate image jump

If FA = +2.50 D with a RD 22 segment…

A

1.1 x 2.50 = 2.75 BD

99
Q

Calculate the Displacement.

If the segment were a +2.00 Add Round 22 bifocal, calculate ΔDD

A

ΔDD = 11-5 = 6 = .6 x 2.00 =

1.2 BD

100
Q

What does Total Image displacement tell you?

A

The sum off both Prism in add and distance

ΔTD) =(dC x FC) + (dS x FS

101
Q

In regards to lens power effectivitty, if the vertex increase what happens to the plus lens?

A

More effective plus lens

102
Q

What is the formula for lens power effectivity?

A

Fn = Fo ÷ (1-dFo)

Fo = BVP needed at the origina vertex distance

Optics 4 (2 decks)

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