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OV2021 dispensing > multifocal lenses > Flashcards

multifocal lenses Flashcards

1
Q

what are trifocals thought of ?

A

. can be thought of as a bifocal with an additive intermediate section

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2
Q

what are trifocals described by?

A

. trifocals are described by segment size

. s= straight top, the depth of the intermediate section and the diameter of the segment
eg s728

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3
Q

how does the size of the intermediate section vary?

A

. the size of the intermediate section varies between lenses
. if px does more intermediate work we are able to extend that
. if px does limited intermediate work , we can make that section smaller

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4
Q

how to work out prescription required in the intermediate section of trifocal?

A

. to work out prescription required in the intermediate section of trifocal
. we use the IP/RP ratio

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5
Q

what is the IP/RP ratio?

A

. IP/RP ratio= (IP add/RP add) x100

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6
Q

what is the most suitable IP/RP ratio ?

A

50-60%

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7
Q

what are the advantages of trifocals?

A

. intermediate section
. full distance portion which is not available in progressive lenses
. no distortion
. wide intermediate and near portion

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8
Q

what are the disadvantages of trifocals?

A

. seg top 3mm above limbus-may interrupt distance vision
. reading portion 2mm lower than bifocals
. 2 areas of jump- if px suffered with jump in bifocals, trifocal isn’t a good option

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9
Q

when to set the segment 2-3mm higher than normal ?

A
  • if a px is getting on with bifocals, but just requires the limited extra near or intermediate use
  • we can set segment 2-3 mm higher than normal
  • make segment easier to assess and give them larger area
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10
Q

what are some occupational trifocal lenses?

A
  1. double D segment trifocal is popular for pilots and other occupations where they will be looking at small detail above and below the eye line
  2. rodenstock C40 datalit trifocal - gives a large area for intermediate and near
    - intermediate is section is 10mm deep
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11
Q

what are varifocal design?

A
  1. hard design

2. soft design

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12
Q

what is the difference between close and far lines in varifocal designs?

A

. know as isocylinder lines

. the closer the lines are together, the steeper that surface astigmatism is , the quicker the px will get to it

. the far apart lines tend to indicate that astigmatism is more gentle

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13
Q

what is a hard design?

A

. has no distortion in distance portion
. good for drivers, golfers

. intermediate is very narrow - - obvious distortion

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14
Q

what is a soft design?

A

. more distortion in distance portion

. wider intermediate section - softer distortion

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15
Q

what is firm / ultra soft design?

A

. combination of hard and soft design

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16
Q

what are freeform design lenses ?

A

. has less surface stigmatism
. available in different fitting heights - suitable for different frames
. they employ computer aided technology in the manufactures , which increases the accuracy of their design

17
Q

what do traditional lenses use to create the progressive surface ?

A

. traditional lenses use a glass mould to create the progressive surface on the front

. this meant no change can be made to the front surface, distance prescription can be worked on the back

18
Q

where do free form lenses have the progressive surface?

A

. can have the progressive surface on the back, front or mixture of both surface

19
Q

what is the benefit of freeform lenses being highly individual?

A

. freeform lenses are highly individual , this helps to compensate for the aberrations and distortions a patient might notice when wearing traditional bifocals

20
Q

what is the benefit of freeform lenses being available in multidesign?

A

. back surface designs which allows modification of lens parameters such as the inset
. we can alter the corridor length - how quickly the patient gets into NV

21
Q

what is the difference between head and eye movers?

A

. patients will either be head or eye movers
. eye movers - experience chromatic aberrations
. head movers - get into varifocals better , because they don’t look into that area of surface astigmatism

22
Q

how does freeform lens put distortion in different areas?

A

. can match astigmatism on right and left eye
. can put distortion in different area
. e.g. if px does a lot of reading , the distortion may be put towards the temporal side instead on nasal side

23
Q

what are the benefits of freeform lenses?

A

. framization -takes into account frame measurement
e.g. pantoscopic tilt

. multidesign - back surface designs which allow modification of lens parameters
e.g. variable inset, corridor length

. physiological - consider head and eye movement

24
Q

what do the freeform lenses take into account ?

A

. the design of freeform lenses changes with

  • right and left eye
  • the level of hyperopia or myopia
  • the add
  • the body posture
  • behaviour
  • frame chosen
25
Q

why are freeform lenses difficult to focimeter?

A

. the focimeter doesn’t adopt a natural wearing position
. powers you read for the focimeter might not be accurate for the lens
. these lenses when dispensed , will often be sent with lens packages which tell you which powers you should be reading on the focimeter

26
Q

what some occupational progressive lenses?

A

. driving lenses
. office lenses
. intermediate/near only

27
Q

what are driving lenses ?

A

. driving lenses concentrate on having wider distance and intermediate section
. have limited near vision section

  • not good for long term NV use
28
Q

what are office lenses?

A
  • give good visual comfort when looking at intermediate and near
  • not good for DV
  • wider corridor for the IV and NV section
  • good for px with indoor use
  • not suitable for driving
  • can be tailored for px depending on the intermediate work they do
  • often coated
29
Q

what are the names of manufactures of office lenses?

A

. zeiss gradal PD
. Varilux digitime room
. Norville bureau HD
- which correct up to 5m- good for office worker

30
Q

what are enhanced readers?

A

. good for patients who do large IV and NV use
. don’t need to look far
. low levels of surface astigmatism
. ordered differently to varifocal design - order them with reading prescription and how much distance prescription you want

31
Q

what are some occupational considerations?

A
  1. visual task analysis
    - ask px about task size
    - ask px about working distance
    - still/moving task
    - position of task and patient
  2. amount of distance vision required
  3. amount of intermediate vision required
  4. amount of near vision required
32
Q

what to do when asking question regarding occupation?

A

. make sure you are specific
e.g. ‘ how many hours a day do you use a computer’

  • how many hours a day are you driving
  • what are the main tasks involved in your occupation
33
Q

what to consider when thinking about task px does?

A
  1. important to know task size and if its still or moving
    . this can affect the amount of distortion the px is aware of

. if task is moving px will benefit from free form lens or an occupational lens

  1. important to consider the position of task -
    - if intermediate task is high , the px will look through the distance section and vision will be blurred
34
Q

what to recommend if working distance is mainly distance

A

. if DV is what they will be using the best - recommend an occupational lens designed for driving

. hard, freeform, occupational varifocals are the best option

35
Q

what to recommend if mainly using IV?

A

. soft , firm or occupational varifocal with a wide corridor for intermediate vision

36
Q

what to recommend if mainly NV ?

A

. freeform or occupational varifocals are the best option

37
Q

what else to consider for occupational lenses?

A
  1. safety
    - lens material
  2. glare from artificial lighting
    - multi antireflection coating
  3. glare from sunlight
    - tints with UV400 coating
    - transitions
  4. sun glare from surface
    - polarised

OV2021 dispensing (7 decks)

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