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Year 2 Clinical Studies and Dispensing > High rx dispensing > Flashcards

High rx dispensing Flashcards

1
Q

What issues can a px face when they have a high rx?

A

Thicker/heavier lenses
Magnification or minification of face through lenses

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2
Q

Define refractive index

A

The ratio of velocity of light in a vacuum to the velocity of light in the medium

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3
Q

What happens to TCA with an increase in RI?

A

Increases

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4
Q

How is TCA measured?

A

V-value

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5
Q

Define density

A

mass per unit volume
i.e. how much of the material is within each unit of volume

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6
Q

Define reflectance

A

% of reflection at each surface

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7
Q

Define specific gravity

A

density of a material relative to the density of water

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8
Q

What does the weight of a lens depend on?

A

Density and specific gravity

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9
Q

What is the n of crown glass?

A

1.523

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10
Q

What is the n of CR39?

A

1.498

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11
Q

What is the n of Polycarb?

A

1.586

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12
Q

What is the n of trivex?

A

1.532

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13
Q

What is the density of crown glass?

A

2.5

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14
Q

What is the density of CR39?

A

1.3

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15
Q

What is the density of polycarb?

A

1.2

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16
Q

What is the density of trivex?

A

1.1

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17
Q

What is the v-value of crown glass?

A

59

18
Q

What is the v-value of CR39?

A

58

19
Q

What is the v-value of polycarb?

A

30

20
Q

What is the v-value of trivex?

A

46

21
Q

What is the reflectance of crown glass?

A

4.3

22
Q

What is the reflectance of CR39?

A

4.0

23
Q

What is the reflectance of polycarb?

A

5.2

24
Q

What is the reflectance of trivex?

A

4.4

25
Q

What measurements do you need to take for SV high index dispenses?

A

Mono PD
Heights to pupil centres with dispenser’s rule applied
BVD

26
Q

What measurements do you need to take for BIF high index dispenses?

A

Binoc PD
Heights to lash line
Inset
BVD

27
Q

What measurements do you need to take for Vari high index dispenses?

A

Mono PD
Heights to pupil centre
BVD

28
Q

At what rx should BVD be taken?

A

+/- 5D

29
Q

If you move a lens away from the eye it becomes more:

A

Plus

30
Q

If you move a lens towards the eye it becomes more:

A

Minus

31
Q

Why should BVD be kept to a minimum?

A

Maximise FOV
Reduce distortion
Reduce chromatic abberation
Reduce mag/minification

32
Q

Why is the correct centration important?

A

Rx most effective when looking through centre of lens
Reduces unwanted induced prism
Reduces possibility of ghost images
Reduces one sided thickness

33
Q

What do you need to consider in terms of the lens for high myopic dispenses?

A

Lens material/form
High index lenses
High v-value
AR coat
aspheric/lenticulars

34
Q

What do you need to consider in terms of the frame for high myopic dispenses?

A

Small frame (to cut off edge thickness)
Centration as central as poss
Thick rims to hide thickness of lenses (e.g. plastic)
If nasal thickness will affect positioning of nosepads

35
Q

What benefits could lenticular lenses have to a high minus px?

A

Reduced aperture reduces edge thickness
Good VA and FOV
Controlled abberations
Can choose from wider range of frames
Reduces face minification
Ok cosmetically
Cheaper than high index

36
Q

Who are lenticulars normally dispensed to?

A

> -12.00D (more common if >-20.00D)
Special assessment px’s

37
Q

What do you need to consider in terms of the lens for high hyperopic dispenses?

A

Lens material/form
High index lenses
High v-value
AR coat
Aspheric/lenticulars
Small blank size

38
Q

What do you need to consider in terms of the frame for high hyperopic dispenses?

A

Centration as central as poss
Small eye size
Good fit to avoid slipping
Lightweight frame material
Regular/Fixed/strap bridge

39
Q

What benefits could lenticular lenses have to a high plus px?

A

Reduced aperture reduces centre thickness
Good VA and FOV
Controlled peripheral abberations
Can choose from wider range of frames
Reduces face magnification
Ok cosmetically
Cheaper than high index
Reduces jack in the box effect

40
Q

Which px’s are lenticular bifocals useful for?

A

High powered presbyopes

41
Q

What measurements are needed for lenticular bifocals?

A

Mono PD
Heights of seg top
Inset
BVD

Year 2 Clinical Studies and Dispensing (14 decks)

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