Multifocals L4 Flashcards

1
Q

How to describe Trifocals?

A

Described by seg height and shape (i.e s = straight top) AND the depth of the int seg and the diameter of the seg eg s72Attach Images8

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2
Q

What is the IP/RP ratio?

A

IP/RP ratio = (IP add/RP add) x 100

[Smaller % means more diatnce vision is available]

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3
Q

Advantages of trifocals?

A
  • Contain an intermediate section
  • No distortion
  • Full distance portion which isn’t available in progressive lenses
  • Wide intermediate and near portions
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4
Q

Disadvantages of trifocals?

A
  • The seg top is set usually higher than we would set a bifocal seg (seg top 3mm above limbus) - which may interrupt distance vision (but this could be set lower)
  • reading portion 2mm lower than bifocals (thus smaller near section)
  • 2 areas of jump
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5
Q

If a px has Occupational Bifocals and requires them for limited extra near or intermediate use what can we do?

A

We can set the seg 2mm higher - this makes the seg easier to access and gives Px larger area to look through.

[Note - this is not suitable for walking around - so only good for occupations where you are sat at a desk]

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6
Q

What are the different types of Trifocals and who are our recommended Pxs for them?

A
  • DOUBLE D - we can prescribe a sep rx above and below, px for this tend to be professions like pilots, plumbers, mechanics. (For job looking at small print above and below eye print).
  • ED seg - Large IV and NV (for px who don’t get on with varifocals but don’t like straight top look of seg)
  • Rodenstock C40
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7
Q

What are hard varifocals?

A
  • 1st generation of design.
  • surface astigmatism is concentrated in lower and nasal areas of the lens - very narrow progression corridor
  • wide reading area and full width distance portion
  • closely spaced isocylinder lines (this refers to the image) = rapid change of astigmatism ( it means there are steep curve changes whihc mean you have more oblique astigmatism which is interpretated by the Px as distortion)
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8
Q

What are soft varifocals?

A
  • 2nd generation of design
  • surface astigmatism extends into marginal parts of distance portion
  • allows a reduction in amount of surface astigmatism
  • narrow reading area and wide progression corridor
  • wider intermediate portion than hard design but blur introduced into distance portion
  • Easier adaptation
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9
Q

What are freeform varifocals?

What are some examples of freeform varifocals?

A
  • Basically customisable varifocal lenses that use Computer aided design to make them specific (and accurate) to the patient.
  • eg varilux s or zeiss individual 2
  • created by computer driven equipment and made to suit each individual specification
  • freeform can have progressive surfave on front, back or both (traditional lenses had progressive surface on the front only)
  • they allow for multidesign - back surface designs which allow modification of lens parameters eg variable inset, corridor length, etc.
  • They are unique to the point where they even consider physiological factors - e.g. consider head and eye movement
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10
Q

In freeform lenses the design changes with:

A
  • right and left eye
  • level of hyperopia or myopia
  • how much add is present
  • body posture
  • behaviour -whether your a head mover or an eye mover e.g. do you turn your head to glance at mirror or look from the edge of your glasses)
  • frame chosen
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11
Q

Effect of increasing the add in varifocals:

A
  • length of the progression corridor increases and the width of the reading area narrows as the add increases
  • increased surface astigmatism leading to isocylinder lines being closer together - px would notice reduction in the width of the intermediate and reading areas
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12
Q

What are compensated areas? Why are freeform lenses difficult to focimeter?

A
  • focimeter position isn’t a natural wearing position
  • (This means measurement is off -effects add mostly, but can also affect DV rx )
  • This is because freeform varifocals have ‘compensated powers’ which take into account Back Vertex Distance, pantoscopic tilt, face form angle, px position - can result in diff readings for sph, cyl and axis - thus they typically come in packets that dictate all parts of the Rx.
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13
Q

What are the different types of Occupational progressive lenses and what are their main features- give examples of each :

A

1) Driving lenses
- eg varilux computer 3v
- widest possible DV and IV with limited NV
2) office lenses
- e.g. zeiss gradal RD
- gives good visual comfort
- Designed for IV and NV but sacrifices DV thus cannot be worn for driving.
- corrects up to 5m
3) Intermediate/ near only or Enhanced Readers
- interview lens
- Larger IV and NV than office lens
- low levels of surface astigmatism
- wide and stable FOV -e.g. good for receptionists
- wouldn’t use these to look at a distance of a whole room away.

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14
Q

What are Occupational considerations to take note of when prescribing any type of multifocal?

A

1) Visual task analysis - task size - contrast - stereopsis - lighting - working distance - still/moving task - affects peripheral distortion - position of task and px (vertical and horizontal) - area of vision
2) amount of distance vision required
3) amount of int vision required
4) amount of near vision required

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15
Q

Which type of varifocal design is best in what cases?

A
  • When mainly distance vision is needed to be considered i.e. for occupations like driving and landscaping, hard/ freeform are best
  • When mainly intermediate vision is needed to be considered e.g. in offices and retail, soft, firm or occupationals are best
  • When mainly near vision is needed to be considered, e.g. for an office worker and product inspection, freeform or enhanced readers are best
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16
Q

What qs to ask about px occupation before prescribing any type of multifocal?

A
  • what is your occupation
  • how many hours a day are you on a computer screen
  • how many hours a day are you driving
  • what are the main tasks involved in your occupation - also consider their hobbies
17
Q

Other occupational considerations that are not related to the distance at which vision occurs, which need to be asked to the Px?

A

1) safety - lens material
2) glare from artifical lighting - multi AR coating
3) glare from sunlight - tints with UV400 coating or transitions
4) sun glare from surfaces - polarised

18
Q

For most people what is a suitable IP/RP ratio?

A

Around 50-60%

19
Q

If a px has suffered with jump in bifocals is a trifocal a good option?

A

No because there’s now two areas of jump as a pose to one in bifocals.

20
Q

What distances can occupational bifocals be set at?

A

DV and IV or IV and NV

21
Q

What type of Px are hard design varifocals best for?

A

Traditionally don’t have distortion in the distance thus good for Px who do distance work e.g. drivers or golfers.

22
Q

How is distortion experienced in a hard design contact lens?

A

Distortion at periphery is abrupt and obvious this can be seen from lines being close together indicating surface change is steeper.

23
Q

How is distortion experienced in a soft design contact lens?

A

It is softer/more gradual than that of a hard design varifocal thus is less obvious.

24
Q
A