clinical skills > Dispensing 2 > Flashcards

Dispensing 2 Flashcards

(51 cards)

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1
Q

What factors do we need to consider in choosing frames and lenses?

A
  • myope
  • hypermetrope
  • astigmatism
  • presbyope- less accomodation due to age so reduces eyes ability to focus
  • current type of specs/lenses
  • occupations: safety
  • Hobbies
  • asthetics
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2
Q

What do people with distance high prescriptions need to consider?

A
  • Lens thickness
  • Lens weight
  • if they are short sighted/myopic the lenses are thicker at edge therefore heavier
  • Power rings- we get when lenses are thicker which causes reflection on the lens.
  • Magnification- eyes look bigger/ Minification
  • Spherical and transverse chromatic aberrations
  • Must record back vertex distance if Rx>5.00D
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3
Q

How can we minimise lens thickness and weight?

A
  • uncut lens gives thinnest lenses
  • myopic lens thickest at edges
  • hypermetropic lens thickest in middle.
  • aim for smallest frame and minimum decentration of lenses
  • ideally boxed centre distance = PD (frame PD = Patient PD)
  • oval frame gives thinner edges for myopic Rx but cuts into thicker part of lens for hypermetropic Rx.
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4
Q

What is refractive index?

A

n= speed of light in air/speed of light in material

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5
Q

What do high refractive index lens do?

A

Slows light down more
refracts light more
therefore much more thinner lens(lens curvature and thickness is reduced)

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6
Q

What is the advantages of high refractive index lens?

A

thinner lens

lighter lens

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7
Q

What is the disadvantage of high refractive index lens?

A
  • more reflections from lens surface therefore need antireflective coating.
  • lower aberration number(V value)- high variation ‘n’ across wavelength- causes transverse chromatic aberrations.
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8
Q

What are the lens materials?

A
  • specific gravity- density of material/water (weight of lens compared to water)-
  • Impact resistance
  • Chemical resistance
  • Scratch resistance
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9
Q

What is the value of n, specific gravity and V value for

  • crown glass
  • CR39
  • Polycarbonate
  • 1.74 plastic
  • 1.9 glass
A
  • 1.523, 2.54, 59
  • 1.498, 1.32, 58
  • 1.586, 1.20, 30
  • 1.740, 1.40, 33
  • 1.885, 4, 31
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10
Q

What is the advantages of crown glass?

A

scratch resistance, optical performance and chemical resistance

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11
Q

disadvantage of crown glass?

A

poor impact resistance.

heavier than plastic

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12
Q

Advantage of CR39?

A

Lightweight, good optical performance

inexpensive

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13
Q

Disadvantage of CR39?

A
  • susceptible to abrasion (hard coat is needed)
  • poor impact resistance
  • Poor UV protection if uncoated
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14
Q

Advantage of poly-carbonate?

A

good impact
resistance
high n
good UV protection

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15
Q

Disadvantage of poly-carbonate?

A

Susceptible to abrasion`

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16
Q

Advantage of plastic?

A

thinner, lighter than CR29

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17
Q

Disadvantage of plastic?

A

expensive
low V value
surface reflections
prone to abrasions

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18
Q

Advantage of 1.9 glass?

A

highest index ever therefore thinnest lenses but high specific gravity (heavy)

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19
Q

Disadvantage of 1.9 glass?

A

expensive
low V value
surface reflections
scratch resistant to crown glass.

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20
Q

What does an aspheric lens do?

A
  • line of curve of lens changes from centre to periphery
  • creates thinner, flatter lens profile
  • reduces spectacle magnification
  • good for high powered Rx
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21
Q

What is power rings?

Study These Flashcards
A
  • caused by internal reflection at the lens edge

- anti-reflective coating and darker frame rims will help

22
Q

what are examples of plastic frame materials?

Study These Flashcards
A

.cellulose acetate
.optyl
.SPX

23
Q

what are the advantages of cellulose acetate?

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A

. inexpensive
. can be laminated or dyed
. adjust at moderate heat
. reinforced sides

24
Q

what are the disadvantages of cellulose acetate?

Study These Flashcards
A

. colour with age and can react with skin to form white deposits

25
what are the advantages of Optyl?
.Safilo registered . can be laminated or dyed . 30% lighter than cellulose acetate . memory plastic
26
what are the advantages of SPX?
``` . nylon based . sides reinforced . impact resistant . flexible . light weight ```
27
what are the types of metal frame materials?
. nickel silver . nickel titanium . titanium
28
what are the advantages of nickel silver?
. inexpensive . easily adjusted . flexible . contains copper , nickel , zinc
29
what are the disadvantages of nickel silver?
. nickel can react to skin
30
what are the advantages of nickel titanium?
.memory metal .50% titanium . 23% lighter than silver nickel
31
what are the advantages of titanium?
. 50% lighter than nickel titanium . flexible . corrosion resistant
32
what are the disadvantages of titanium?
.. hard to repair | . expensive
33
what are the advantages of using plastic as frame material?
.resistant to permanent deformation when dropped . easy to mould .more hypoallergenic than metal
34
what are he disadvantages of using plastic as frame material?
. tend to have fixed bridges rather than pads .more breakable than a metal frame . tend to be heavier
35
What is power rings?
- caused by internal reflection at the lens edge | - anti-reflective coating and darker frame
36
What lens can help with magnification/minification?
Aspheric, however it is largely unavoidable
37
What lens cause minification?
myopic- make world look smaller to px, and the px's eyes look smaller to everyone else (minification)
38
What lenses causes magnification?
Hypermetropic
39
What are the 3 lenses to correct presbyopia?
trifocal varifocal bifocal
40
How does the d seg bifocal appeear?
looks like a D and the near is in the bottom and distance at top
41
How does the e seg bifocal appear?
line goes across whole lens
42
How does R seg bifocal appear?
round shape
43
What is a E-D trifocal?
has distance at top, intermediate where the line goes across the lens and near at the bottom in the D shape
44
What is a double D trifocal?
Intermediate or near at the top distance in middle intermediate or near at the bottom
45
What is a Progressive lens (known as varifocal)?
distance at top intermediate in the middle reading/near at the bottom The power varies over the lens so there is no line going through the middle of the lens
46
What is the advantage of anti-reflective coating?
using a computer | aesthetics
47
disadvantage of anti-reflective coating?
attract dirt and smudges
48
advantages of tint?
driving | outside
49
disadvantages of tint?
distort colour | doesnt allow enough light into the eye
50
advantages of blue light?
someone who uses computer
51
disadvantages of blue light?
can have a tint which people may n ot like
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