Multifocals L4 Flashcards

1
Q

How to describe Trifocals?

A

Described by seg size sg s = straight top, the depth of the int seg and the diameter of the seg eg s728

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2
Q

What is the IP/RP ratio?

A

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

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3
Q

Advantages of trifocals?

A
  • Int section
  • No distortion
  • Full dist portion which isnt available in progressive lenses
  • Wide int and near portions
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4
Q

Disadvatages of trifocals?

A
  • seg top 3mm above limbus - may interrupt dist vision
  • reading portion 2mm lower than bifocals
  • 2 areas of jump
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5
Q

Occupational Bifocals

A
  • can dispense IV/NV instead of DV/NV

- set seg 2mm higher

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6
Q

Different types of Trifocals

A
  • DOUBLE D - we can prescribe a sep rx above and below, people need this like mechanics and plumbers
  • ED seg
  • CONCENTRIC DOWN CURVE
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7
Q

What are hard varifocals?

A
  • 1st generation
  • surface astigmatism is conc in lower and nasal areas of the lens
  • very narrow progression corridor
  • wide reading area and full width distance portion
  • closely spaced isocylinder lines = rapid change of astigmatism
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8
Q

What are soft varifocals?

A
  • 2nd gen
  • 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 int portion but blur introduced into dist portion
  • Easier adaptation
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9
Q

What are freeform varifocals?

A
  • eg varilux s or zeiss individual 2
  • created by computer driven equipment and made to suit each individual specification
  • traditional lenses had progressive surface on the front
  • freeform can have progressive surfave on front, back or both
  • multidesign - back surface designs which allow modification of lens parameters eg variable inset, corridor length
  • physiological - 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
  • add
  • body posture
  • behaviour
  • frame chosen
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11
Q

Effect of increasing the add:

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 int and reading areas
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12
Q

What are compensated areas?

A
  • focimeter position isnt a natural wearing position
  • effects add mostly, but can also affect DV rx
  • compensated powers take into account BVD, pantoscopic tilt, face form angle, px position
  • can result in diff readings for sph, cyl and axis
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13
Q

Occupational progressive lenses:

A

1) restricted vision
- eg varilux computer 3v
- full distance rx reached in lens

2) office lenses
- zeiss gradal RD
- corrects up to 5m

3) Intermediate/ near only or Enhanced Readers
- interview lens
- good for pxs who prev had SV near
- low levels of surface astigmatism - wide and stable FOV

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14
Q

Occupational considerations

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

Working distance considerations

A
  • When mainly distance for occupations like driving and landscaping, hard/ freeform are best
  • Whne mainly int vision eg offices and retail, soft, firm or occupationals are best
  • when mainly near vision, eg office worker and product inspection, freeform or occupationals are best
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16
Q

What qs to ask about px occuaption?

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 occuaptional considerations?

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