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OV2021 dispensing > Varifocals > Flashcards

Varifocals Flashcards

1
Q

What do our single vision glasses allow ?

A

for the px to see the prescription through the whole lens

  • concentrating on a task fro a long period of time
  • no good for multitaskers
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2
Q

Why do px with reading glasses pull their glasses down ?

A
  • to give themseleves a multifocal lens

- look over top of lens for distance and bottom for reading

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3
Q

Why do px go for bifocals?

A

-focuses at distance and near

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4
Q

What are varifocals?

A
  • focuses at distance , intermediate and near
  • provide gradual change in prescription
  • think about trifocal lens but with lines rubbed out
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5
Q

What are some advantages of varifocals?

A
  • no jump- smoother transition- no visible lione
  • good cosmetics- no lines- not indicative of older age
  • look like a SVD
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6
Q

What are some disadvantages of varifocals?

A
  • peripheral distortion - to the sides of the lenses
  • lot of horizontal head movements are therefore required for px to get on with these lenses- particularly with older types of varifocals
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7
Q

What are enchanted readers/ occupational lenses ?

A

are a form of varifocal where the emphasis on the prescription - largest portion of the lenses is given to the intermediate or near vision unlike the varifocal that is given its largest portion to the distance.
-they allow limited distance vision

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8
Q

What are occupational lenses good for ?

A
  • good for viewing presentation on screen
  • larger zone for near/intermediate work

-

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9
Q

What are occupational lenses not good for ?

A
  • not suitable for driving in
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10
Q

What does the varifocal progressive surface vary in ?

A

it varies in curvature to provide a gradual increase in positive powered down along a central corridor

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11
Q

What does the change in radius of curvature of varifcoal lens do ?

A

cause change in prescription

-prescription is based on r.i of lens

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12
Q

What is the material in the varifocal ?

A

lens is all one material

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13
Q

What happens to the radius of curvature as you go down the varifocal lens ?

A

gets steeper

  • which is increasing this + power
  • elephant trunk design
  • r.o.c getting smaller as we get to bottom of lens
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14
Q

Where is varifocal most clear at?

A

only clear in central viewing corridor

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15
Q

So what happens to varifocal due to changes in curvature at the edges ?

A

-the change of curvature that produces more positive prescription towards bottom of lenses also introduces surface astigmatism

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16
Q

Where does surface astigmatism occur ?

A
  • at the nasal and temporal sides of the lens-
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17
Q

What does surface astigmatism create ?

A

creates unwanted cyl power- resulting in areas of blur and distortion

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18
Q

What is the amount of surface astigmatism experienced on lens proportional to?

A
  • to addition power

- the higher the add the px has - the more distortion the lens has

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19
Q

What is the distribution of surface astigmatism dependant on ?

A

-on design of lens- some have more than other- generally newer / expensive lenses are better

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20
Q

Who are the best candidates for varifocals?

A
  • Previous progressive lens wearers
  • Emerging presbyopes with a low Add power
  • Individuals who are highly motivated
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21
Q

Who are the

candidates that require consideration include:?

A
  • Presbyopes with a relatively high Add power (>+2.25)
  • Previous wide-segment bifocal wearers - area you get Is less in varifocals
  • Individuals sensitive to vertigo or motion sickness - due to head movement requirements
  • Individuals particularly sensitive to changes in vision
  • Those with a vertical imbalance or anisometropia
  • Eye movers/ people who require wide visual areas
22
Q

What is the fitting procedure for varifocals ?

A
  • make sure px sits comfortably
    -select the frame
    -pre adjust the frame- before you begin- so make sure px area of vision will fit into the frame they have chosen
    -amount of measurement depends on lens you choose
    -MSU
    -Measure the fitting heights
    §Measure the distance PDs
    §Verify blank size
    §Take free-form measurements (if necessary)
23
Q

How do we dispense varifocals ?

A
  • Take PD
  • THINK horizontally- px eye is lined up centrally in the corridor vision- to give them as much vision as possible
  • take monocular PD
  • cant assume px is exact same distance to nose
  • THINk position of pupil vertically- make sure px is starting the progression zone at the right point (From distance to intermediate to reading)
  • take heights
24
Q

What is monocular PD?

A

distance from centre of pupil to the centre of bridge of nose

25
Q

How do you take the vertical measurements when dispensing varifocals? (HEIGHTSP)

A
  • using horizontal centre line
  • measure from centre of pupil to HCL
  • whilst you measure this point- look at centre of pupil to bottom of rim- manufacturers will specify how long that zone needs to be make sure the lens fits in all the vision
  • face wrap/face tilt
26
Q

Why are heights also taken?

A

to make sure the lens are positioned properly

  • also to make sure the lens will fit into the chosen frame
  • manufacturers will specify from the centre of pupil and top of lens- to make sure the amount of distance vision can fit in
27
Q

What is the required frame depth\?

A

pupil centre to bottom of lens - is 14mm (result in areas of Intermediate and near ebbing smaller and transition being quicker- not all px tolerate this
-some px prefer a longer corridor- that gives more gradual change in prescription - make sure that shorter corridors are wanted or not.

28
Q

What happens if a frame is too small for required depth?

A
  • px misses out on some d vision and n vision

- make sure frame choice is suitable for the Lens given

29
Q

What happens if frame is big but sits quite high on px bridge?

A

they still might not have enough area for near vision

  • in this case you can adjust the frame so its in the correct space- where pupil would sit centrally- s
  • or might have to change the frame- if cant get too sit in the right place
30
Q

What are some other measurements to how px sees through their varifocals?

A

pantoscoptic tilt

31
Q

Why is pantoscoptic tilt important in varifocal lenses?

A

brings near vision closer to the eye which increase the field of view

  • area for reading little larger
  • optical and visual axis of lens are aligned when px is looking down to read
32
Q

How can pantoscoptic tilt help?

A

just by increasing this can make a large difference to how much they are seeing

33
Q

What happens if px has a orthoscopic angle or retroscopic angle ?

A
  • the lens is almost bending outwards from the bottom- going to need to alter that sitting on px head- look at frame from side
  • or alter on the frame
34
Q

What is face wrap / face tilt ?

A
  • isn’t required for all varifocal lenses but required for many of the free form Lens designs
  • inclination of the temporal edge of each lens towards the face- makes sure the front of the frame is following naturally the shape of the skull
  • peripheral distance zone closer to the eye- increasing the field of view
  • also moves the peripheral areas of distortion out of the wearers immediate field of view
35
Q

Why might px not tolerate varifocal lenses?

A
  • incorrect prescription or measurements - technical
    -misunderstanding of measurements
    -px not sat correctly or frame not sat correctly
    -have to make sure px has a natural head position when taking measurments
    -not been educated on what to expect
    -
36
Q

what is the distance between the 2 engraving dots?

A

always 34mm

-alignment distance markings

37
Q

What is the engraved temporally ?

A

will be the reading addition

e.g 15- means 1.50

38
Q

What is engraved nasally?

A

manufacturers mark

  • brand of lens
  • supplier
39
Q

What is the fitting point?

A

-where you want the distance prescription to start- line up with px pupil

40
Q

What is the prism reference point ?

A
  • where we measure any prescription we find in a varifocal lens
  • dont measure at fitting point
41
Q

What is near vision checking point ?

A
  • vision at near portion
  • due to design of varifocal more better to use engraving
  • but can draw if you feel like px hasn’t got full area of vision in near
42
Q

Why do we measure the prism from reference point rather than any other point on the lens?

A

prism thinning

43
Q

Why do we do prism thinning ?

A
44
Q

What does prism thinning do ?

A

-so therefore prism thinning is used to equalise the thickness of the top and bottom of lens

45
Q

What does prism thinning do ?

A
  • so therefore prism thinning is used to equalise the thickness of the top and bottom of lens
  • making thickness equal throughout lens
46
Q

How do we do prism thinning ?

A

remove base up prism from the top of the lens- which makes that part of the lens thinner

  • leaves us with base down prism- work on 2/3rds of the addition .
  • some manufacturers use intelligent thinning
47
Q

What is intelligent thinning ?

A

calculate the amount of base down to put with the lens to produce the best finished result

48
Q

What happens if px does not have prism in their prescription ?

A

-looking at prism reference point even if px does not have any prism you will find 2/3rds of the add at that prism point

49
Q

Why do px get on with this well ?

A
  • same right and left
  • no problem when px looks down to read as the amount of prism they experience at near vision point is equal
  • however if they have different adds to right and left eye- will be problem -can request lens without thinning
50
Q

How to choose a progressive lens?

A
  • look at the size and location of the useful areas of vision they require- (e.g large intermediate area, or distance etc)
  • think of width and length of corridor vision- (E.g what px needs as part of their visual task analysis but also from the Frame they have chosen and where it sits)
  • the rate of power change in the corridor
  • the location , magnitude and axis of unwanted spy and cyl refractive powers - if px has suffered with distortion in the past - wants to use a lens where less distortion and place the lens so px doesnt look through it
51
Q

What to make sure you discuss with px?

A
  • pros and cons with px
    -Head movement ØPeripheral distortion ØChange in Rx over lens
    § Demonstrate
    § Adaptation period
    § What to do if there is no progress § Confidence
    § Talk positively!

OV2021 dispensing (7 decks)

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