dispensing 1 Flashcards

1
Q

what are the issues of having a high power Rx?

A

-the lenses are thicker so more conspicuous
-heavier since more volume of lens
-spectacle magnification/ minification making faces appear larger/ smaller

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2
Q

what are the 4 types of plus lenses?

A

-equi-biconvex
-biconvex
-planoconvex
-meniscus forms

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3
Q

what are the 4 types of minus lenses?

A

-equi-biconcave
-biconcave
-planoconcave
-meniscus forms

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4
Q

How do you calculate CVF?

A

(n’-1)/(n-1)

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4
Q

what measurements do you need for HI Single vision (SV) lenses?

A

Mono. PD
Heights of pupil centre (Dispenser’s Rule applied – DV only)
BVD

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5
Q

what measurements do you need for High index (HI) bifocals (BIF)

A

Binocular PD (Mono. PD if Rx>8D or face asymmetrical)
Inset
Heights at lower limbus
BVD

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6
Q

what measurements would you take for high index varifocal lenses (PPL)?

A

Mono. PD
Heights of pupil centre
BVD

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7
Q

how do you find densitiy

A

density = mass per unit volume

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8
Q

how do you work out specific gravity?

A

density of a material relative to the density of
water (which is 1g/cm3)

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9
Q

why should BVD be kept to a minimum?

A

-maximise FOV
-reduce distortion
-reduce chromatic aberration

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10
Q

why is it important to correct centration?

A
  • correct Rx most effective in front of pupil
  • reduces unwanted differential prism
  • reduces possible formation of ghost
    images
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11
Q

what are the effects of inwards decentration of high power lenses

A

-increased temporal edge thickness in negative lenses
-increased nasal edge thickness in positive lenses

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12
Q

why can dispensing in high myopia be a problem?

A

because of edge thickness

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13
Q

what can help dispensing lenses with high myopia?

A

-lens material and form
-high index lenses
-high v value (abbe number)
-AR (anti reflection) coating
-aspheric or lenticular lenses

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13
Q

how can you improve frames in high myopic glasses?

A

-little to no decentration frame
-small eye size
-plastic rimmed and thicker rimmed metal frames support and help hide edge thickness

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13
Q

what are polynomial lenticulars vs standard lenticulars

A

polynomials have a gradual change between margin and centre whereas standard have a sudden change between margin and centre

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13
Q

what is the aperture of a lens?

A

the area in the centre of the lens that have the Rx

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13
Q

what are lenticular lenses?

A

reduced aperture lense

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13
Q

what are the benefits of lenticulars

A

-good vas
-good FOV
-controlled aberrations
-improved edge thickness and mass
-allows wider frame selection
-help remove minifcation of the face

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14
Q

what are the main concerns of dispensing for a high hpermetrope?

A

-nasal edge thickness
-centre thickness
-weight

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14
Q

what kind of prescription are lenticulars dispensed for?

A

+-12D

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15
Q

what helps high hypermetropia lenses?

A

-lens material and form
-HI lenses
-high V value
-AR coating
-aspheric or lenticulars
-small blank size

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16
Q

what helps dispensing frames for high hypermetropes?

A

little/no decentration
-small eye size,
good fit to avoid
slipping as ‘front heavy’, consider regular, fixed pad bridge and strap
bridges
-choose lightweight frame material

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16
Q

what affects can high hypermetropia lenses have and how can these be improved?

A

jack in the box effect, can be reduced with lenticulars

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17
Q

what kind of patients would be good candidates for bifocal lenticulars

A

high powered presbyopes

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18
Q

what coatings are used in sports eyewear?

A

-MAR (anti reflective coating)
-hydrophobic coatings
-smudge resistant coatings

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19
Q

what filters are used in sports eyewear?

A

-image enhancement
-UV and IR protection

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20
Q

what categories does sports eyewear need to cover?

A

-visual correctiom
-maximum field of view
-safety so has impact resistant
-protection against foreign bodies like dust/dirt
-practical

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21
Q

what are the 7 benefits if wearing contact lenses instead of spectacles in sport?

A

Wider field of view
Reduced magnification/minification
Enhanced depth perception
Fewer aberrations and reflections
Lenses not exposed to environmental conditions e.g. rain,
dirt etc.
Protect against UV
Lesser risk of damage or loss

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22
Q

what features should glasses being worn by people who play racquet sports have?

A

-lenses should be made of polycarbonate / trivex
-close fitting nylon goggles
-silicone bumpers/ side shields as they can take the impact on bridge and temples if hit providing impact resistance and prevent fractures of the orbit
-should ideally be worn with a headband to keep in place

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23
Q

for skiing and snowboarding, what material should spectacle lenses be made of?

A

polycarbonate as it provides robustness and has anti-fogging properties

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24
Q

what are the qualities of polycarbonate lenses?

A

-anti fog
-scratch resistant
-impact resistant
-very flexible
-can be thermoformed to any shape

25
Q

for skiing and snowboarding what coating should you put on the spectacles?

A

100% UV protection - mirror coatings good for reflecting back UV and reducing glare (do not use polarised lenses as not advised for safety because they remove the contrast making it harder to see details in snow surface)

26
Q

what should skiing and snowboarding glasses be made of?

A

nylon, propionate or rubber so they dont go brittle in the cold

27
Q

how do skiing and snowboarding add protection?

A

they have large wrap around goggles / masks to shield the eyes

28
Q

for skiing and snowboarding glasses, what filter should be used?

A

BS EN 12312 states the use of Filter Category 4 i.e. at least 15% LTF

29
Q

for skiing and snowboarding glasses, would you use tints?

A

yes as they improve contrast

30
Q

when are tints available in diving masks?

A

When using 4mm CR39 to increase contrast

31
Q

what are the features of a diving mask?

A

-Full mask with polycarbonate frame and
silicone skirt with well-fitting seal and nosepiece
-With tempered infinity glass flats when no Rx
-Available with Rx glazed insert giving wide
FOV
-Available in custom Rx glass-bonded
lenses
-Usually have option to have gauge reader as BIF
-Sometimes limited to standard OCs (would need to compensate for BVD
change)

32
Q

when dispensing for children, what should a well fitting frame have?

A

the frame PD should be the same as the patient’s PDs

33
Q

when dispensing glasses for a highly myopic child, what should you look for in the glasses you choose?

A

-plastic frame to hold the lens and hide some edge thickness frames
- wide sides help hide edge thickness and give durability
-rectangular in shape

34
Q

when dispensing glasses for highly hyperopic children, what should you look for in the glasses you choose?

A

-a lens as small as possible to try and minimise the blank size (MSU)
-round oval shape

35
Q

what can sport bands be used for in paediatric dispensing

A

to keep the frames in place

36
Q

what do sprung hinges do in glasses?

A

make the frame more durable

37
Q

what 3 lens properties are important in paediatric dispensing?

A

-impact resistance and durability
-that they are relatively thin and lightweight so better comfort and both child and parent can be happier with cosmetic outcome
-they protect against UV as UV radiation dangerous to developing eyes and skin

38
Q

how much UV protection should children’s glasses have in nm

A

at least 380nm up to max of 400nm

39
Q

how can you make communicating with children more effective?

A

-Use familiar words - use short sentences
-Think about the order of words in sentences
-Ensure you are at eye level when you speak to your px
-It is best to speak directly to the child whilst including the parent
-Try and keep the conversation light, laugh with the px and have fun
-It is important they feel welcome in
practice so that they are happy to return
-Try giving the child a sticker as a reward when they leave

40
Q

what are prismatic readers?

A

ready readers with base IN prism

41
Q

what do prismatic readers do?

A

Relieves eye strain when focussing on
close objects
Aids convergence
Good for occupations requiring
prolonged NV at short working distance
e.g. tailor, jeweller etc.

42
Q

who is a ptosis prop for?

A

pxs with a droopy upper eyelid which can be due to trauma to the levator muscle or damage to the oculomotor nerve. this may be caused by diabetes or brain tumour

43
Q

what is a ptosis prop? what is it for?

A

Metal silicone-covered support fitted to upper back plane of spex, holds up droopy upper lid as a short term measure for those awaiting treatment e.g. botox

44
Q

what is the negative of a ptosis prop?

A

Pxs unable to blink freely so lubricant drops needed

45
Q

what measurements are needed for a ptosis prop?

A

length of support (A) and distance from back plane of spex to upper lid (B)

46
Q

who can be dispensed with myopia control spectacles?

A

teenagers/ children who have increasing myopia

47
Q

name the 2 myopia control spex on the market

A

HOYA introduced MiYOSMART 1st followed by Essilor who introduced Stellest

48
Q

what is a feature of myopia control glasses?

A

they have either highly/ slightly aspherical lenslets

49
Q

what are the 4 types of protective eyewear?

A

-afocal one-piece
-box type goggles
-cup type goggles (used very infrequently as they are uncomfortable)
-face shields or visors

50
Q

what is housing and oculars in protective eyewear?

A

housing = frames
oculars = lenses

51
Q

what are box type goggles made of?

A

housing is usually polyvinyl chloride (pVC) and oculars made of polycarbonate or cellulose acetate and have no Rx

52
Q

what are face shields or visors useful for?

A

allow for good protection against splashes and flying particles

53
Q

what are afocal focal one piece protective eyewear? What are they made of?

A

wrap around eye protection - they are the most basic and they generally manufactured in only one size - made of polycarbonate

54
Q

what do most protective eyewear protect against?

A

mechanical impact

55
Q

why are frames in protective eyewear usually made of plastic not metal?

A

as its safer

56
Q

on protective eyewear, what should side shields be made of?

A

a transparent and vented material which is normally polycarbonate

57
Q

what standard does protective eyewear need to conform to and where was this standard derived from?

A

he European standard EN 166 (2002), from the practical test of to drop the ball from a height of 1.3m

58
Q

what practical test does the oculars and housing of protective eyewear need to meet for increased robustness S

A

Oculars - 22mm diameter steel ball of 43g @ 5.1 m/s
Housing - 6mm diameter steel ball of 0.86g @ 12m/s

59
Q

what practical test does protective eyewear need to meet for low energy impact (F)

A

6mm diameter steel ball of 0.86g @ 45 m/s

60
Q

what practical test does the oculars and housing of protective eyewear need to meet for medium energy impact (B)

A

6mm diameter steel ball of 0.86g @ 120 m/s

61
Q

what practical test does the oculars and housing of protective eyewear need to meet for high energy impact (A)

A

6mm diameter steel ball of 0.86g @ 190 m/s

62
Q

how should protective eyewear oculars be marked?

A

-manufacturers mark
-Optical class (1 = continuous, 2 = occasional, 3 = intermittent) – 1 most common
-If present, impact grade (usually S, F, B or A)
There may be a Kitemark, which is not a regulatory requirement, but a
manufacturer’s stamp of quality.

63
Q

how does housing of safety spectacles need to be marked?

A

-Manufacturer’s mark,
offering traceability
(plus Kitemark, not a
requirement).
-EN 166 (relevant standard).
If present, impact grade (F,B or A as no marking on housing are
required for Grade S, increased robustness).
-CE / UKCA mark - products must meet legal requirements before sold
within the EU

64
Q

what materials are used for plastic protective oculars?

A

-polycarbonate
-trivex
-columbia resin 39 (CR39)

65
Q

what is the most commonly dispensed ocular material?

A

polycarbonate

66
Q

what is the positives and negatives of using polycarbonate as ocular material for safety specs?

A

Advantages
-highest impact resistance of all safety ocular materials
disadvantages
-low abbe number so colour fringing
-very soft
-resistance to common chemicals is negligible

67
Q

what is the positives of using trivex as ocular material for safety specs?

A

what is the positives and negatives of using polycarbonate as ocular material for safety specs?

68
Q

what are the two methods of toughening glass and what is the preferred method of the UK?

A

-heat toughened glass and chemically toughened glass
-heat toughened is preferred

69
Q

what us vital when you dispense safety specs?

A

making patient’s case records

70
Q

once supplied and fitted, what happens if safety specs get damaged?

A

no repairs should be carried out on the eyewear. Should be returned to the original manufacturer and replaced to maintain the manufacturers guarantee.