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Ophthalmic Optics Exam 2 + Final Material > Multifocals Lenses > Flashcards

Multifocals Lenses Flashcards

1
Q

2 different types of add on lenses

A

Cemented bifocals & fresnel D seg

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2
Q

What are cemented bifocals?

A

Small plus lens glued to the back. Good optics but collects dirt and could fall off

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3
Q

What are fresnel d seg lenses

A

Sticker on lenses can be temporary but poor optics

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4
Q

What are fused bifocals

A

Small high n glass inserted into a hole in the front of the lens. (Only in glass so aberrations)

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5
Q

What is an up curve bifocal? Advantages and disadvantages

A

Lens was ground for reading rx and the distance portion was made flatter to reduce the plus. Invisible line but aberrations and BD prism on the distance rx

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6
Q

What is the perfection bifocal

A

2 lens held to get her by a groove. Difficult to manufacture

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7
Q

Modern one piece bifocal

A

Increased plus by grinding a different curve on the front or back of the lens, can feel the ledge

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8
Q

What bifocals are change of curvature

A

On piece
Perfection
Up curve

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9
Q

Which bifocal has a change in refractive index

A

Fused bifocals

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10
Q

Seg width

A

The size of a bifocal or trifocals segment measured across its widest section

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11
Q

Seg depth

A

The longest vertical dimension of the lens segment before the lens has been edged

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12
Q

Seg height

A

Vertically measured distance from the lowest point on the frame to the level of the top of the segment

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13
Q

Seg insert

A

The lateral distance from the PRP to the OC of the segment

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14
Q

Seg drop

A

the vertical distance from the PRP to the top of the segment

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15
Q

Flat tops/ D segments:
Seg OC is:
Advantages
Disadvantages

A

Seg OC is 5mm below ledge

Cheap and light

No intermediate

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16
Q

Round segs

A

-Used to be used with hig index but now available in plastic called a blended bifocal

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17
Q

What is a ultex bifocal

A

Round segment with large diameter for a larger reading area

Rarely used

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18
Q

Round segs disadvantages

A

Narrow FOV
In the way of distance
The oc is in the middle of the round segment so high image jump

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19
Q

Executive bifocal?
Advantages ?
Disadvantages?

A

The add seg covers the whole bottom half of the lens
Front surface is ground with a smaller radius of curvature
OC is at the top of the seg

_Wide FOV , no image jump
- heaviest bifocal, edge chops, thick ledge is obvious

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20
Q

Curved top seg

A

Oc is 2 mm higher than FT which allows for easier access to the wider part of seg.
Fewer reflections than FT
But same disadvantages as FT

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21
Q

Ribbon seg/ b segment

A

Ft but with button cut off.
Small depth of seg reduced riding area
2 lines increases reflections
( can be used with one eye and other eye FT to reduce vertical imbalance)

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22
Q

Is an usual lens, as gaze moved away from the OC,

A

Prims is progressively experienced , the effect is gradual and wearer is unaware (prentice rule)

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23
Q

When there is a second lens attached to the main one. The Gradual increase is interrupted

A

Image jump

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24
Q

What is image jump?

A

The apparent displacement of an object as the eye crosses the top edge of the segment (independent if distance RX)

25
Q

What else is seen during image jump?

A

Scotoma of visual information

26
Q

What bofical has no image jump

A

Executive because oc is right at the edge

27
Q

Which bifocals show the most image jump

A

Round segs/ ultex

Because oc is in the center of the circle ( far for top of seg)

28
Q

Where is the OC in flat bifocals

A

5mm from top

29
Q

Where is the OC in round bifocals

A

Diameter/2 (different for all kinds)

30
Q

Oc of ultex is usually

A

19 (huge image jump)

31
Q

In image jump, the further the separation between the segment OC and the top of the segment

A

The more pronounced the effect (image jump)

32
Q

What is the typical intermediate power in a trifocal?

A

1/2 of the near add power, but can depend on their intermediate needs

33
Q

FOV of trifocals is

A

Decreased so used with caution for computer add

34
Q

When can trifocals be considered

A

> +1.50 add struggle to see intermediate

Mechanics/ card players

35
Q

What are the different types of trifocals and the numbers use to describe them?

A
  • Flat top trifocals ( first # how tall the intermediate seg is, second # how wide the segment )
  • E/D trifocal ( executive with a D seg) executive is for intermediate, D seg is for reading)
  • Executive trifocal (franklin)
36
Q

How do we fit trifocals?

A

Lower pupil margin to the deepest part of the frame

Bifocal- lower eyelid

37
Q

What are occupational multifocals?

A

Lens styles that are specifically designed with certain work circumstances in mind

38
Q

What is a double segment lens

A

Occupational bifocal
Pt can view overhead tasks at near viewing distanced
Top and bottom usually have same power

39
Q

Quadrafocal lens

A

4 different powers

40
Q

Golfers bifocal

A

Near is at the inferior temporal of the lens usually on one eye
Can write down score but see ball when looking down

41
Q

Rede rite bifocal

A

Distance is a circle at the top. Rest is near rx

42
Q

In a PALS lens the add increases in the central region which is called

A

Corridor or channel

43
Q

Progressive/intermediate Zone of a PALS?

A

Transition between distance and near zones where clear vision is possible

44
Q

How is the additional power achieved in a PALS ?

A

Variable curvature/ continually shrinking spheres
Horizontally the curves are different radii
The amount of cyl is related to the rate of power change

45
Q

Base curve of PALS

A

Min value at upper distance and max value at lower near portion

46
Q

Prism thinning

A

Equal amounts of vertical prism can reduce the overall thickness/thickness difference

BU is removed
Vertical prism is equal in each eye -> no prism imbalance

47
Q

What are disadvantages of variable curve PALS

A

Unwanted astigmatism/distortIon at the bottom

Blur/swimming sensation

48
Q

The degree of distortion in a PALS lens is influenced by

A 
Add power (higher add-narrower corridor) 
Length of the corridor (shorter corridor) 
Width of the distance and near zones (affect size of corridor)
49
Q

The amount of unwanted cyl is represented as an ______ plot. Which are unique to___.

A

Isocylinder plot

Unique to the brand of PALS and the rx

50
Q

2 design policies of PALS

A

Hard and soft

51
Q

What are hard pals

A

Concentrates distortion into smaller areas expanding the area of clear vision requiring less head/eye movement. But creates higher levels of blur and narrow corridor

52
Q

What are soft pals

A

Spreads distortion across larger areas reducing blur and creates larger corridors. But narrows the distance and near zones of clear vision requiring more head movement

53
Q

What type of design is the newer PALS

A

Between short and hard design

54
Q

Horizontal symmetry in PALS

A

Minimizes difference in induced cylinder between corresponding points on the nasal and temporal sides of the corridor

55
Q

PAL disadvantages include

A
  • Adaptation period to peripheral distortion
  • having a narrow intermediate area
  • need head movement
56
Q

OPLs /occupational progressives

A

Computer progressives have a wide intermediate and near zones with low levels of peripheral astigmatism

57
Q

How to fit a pt in a PAL

A

Monocular PD

Seg height is measure from the center of pupil to deepest part of frame

58
Q

What are additional measurements to individualize PAL lenses?

A

Frame
Patient ( arm length)
Measure w mm ruler

Ophthalmic Optics Exam 2 + Final Material (3 decks)

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