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OP2201- Dispensing > 1. Progressive Lenses > Flashcards

1. Progressive Lenses Flashcards

1
Q

3 common names for progressive lenses?

A
  1. PAL- Progressive Powered Lenses
  2. PPL- Progressive Addition Lenses
  3. Varifocals
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2
Q

3 distinct zones in progressive lenses

A
  1. Distance – a stable zone in the upper portion of the lens that incorporates the necessary distance prescription.
  2. Near – a stable zone in the lower portion of the lens that incorporates the required near addition.
  3. Intermediate – a ‘corridor’ in the central portion of the lens
    that connects the distance and near correction. It is not stable
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3
Q

Is the intermediate portion of progressive lenses stable?

A

The intermediate zone is not stable
but increases in power from distance to near for mid-range vision.

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4
Q

Advantages of progressive lenses?

A
  1. Clear vision at all distances.
  2. More convenient than using 2/3 separate pairs.
  3. Cosmetically, they look like single vision lenses i.e. no visible dividing line.
  4. No image jump occurs as the patient looks down the lens.
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5
Q

Disadvantage of progressive lenses?

A
  1. Distortions in the periphery
  2. Limited field of view for reading
  3. Intermediate and reading areas in a PPL will always be smaller than those in a bifocal
  4. Period of adaption required
  5. Transition between distance and near is narrow so accurate centration is required
  6. Usually, no control of inset
  7. Higher cost
  8. More horizontal head movement needed when reading
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6
Q

Power distribution in PPLs? Upper and Lower portion of lens?

A

Upper portion: Minimum value
Lower portion: Maximum value

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7
Q

What is surface astigmatism?

A

In progressive lenses the change in curvature from distance to near results in unwanted surface astigmatism

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8
Q

What happens if surface astigmatism is in suffient quantity?

A
  1. Blurs vision
  2. Limits wearer’s field of clear vision
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9
Q

By design areas of unwanted astigmatism are in lower quadrants on either side of the intermediate corridor and the near area, why?

A

Less noticeable to the wearer

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10
Q

During dynamic vision, unwanted astigmatism results in?

A

Results in a disturbance called “swim”

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11
Q

Unwanted astigmatism is affected by what 3 factors?

A
  1. Add Power
  2. Length of progressive corridor
  3. Width of the distance and near zone
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12
Q

Relationship between add power and unwanted astigmatism?

A

Amount of astigmatism is proportional to lens add power

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13
Q

Relationship between length of progressive corridor and unwanted astigmatism?

A

Shorter corridors produce more rapid power changes along the corridor and higher levels of astigmatism - reduces eye movement required to reach the near zone.

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14
Q

Relationship between unwanted astigmatism and width of the distance and near zones?

A

Wider distance and near zones have wider fields of clear vision, confine astigmatism to smaller regions of the lens surface on either side of the corridor, but produce higher magnitudes of unwanted astigmatism

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15
Q

3 progressive lens designs are?

A
  1. Hard designs
  2. Soft designs
  3. Firm (super soft) designs
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16
Q

Describe hard design progressive lenses?

A
  1. Larger distance area, short and narrow intermediate corridor with rapid increase in plus power and wide reading area.
  2. Peripheral distortions confined to limited nasal and temporal areas.
  3. Distance virtually distortion free.
  4. Good for previous bifocal wearers.
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17
Q

Describe soft design progressive lenses?

A
  1. Distortion extends to distance area which affects peripheral vision.
  2. Px will have to move head more to view objects in the periphery.
  3. Wider and longer intermediate corridor that increases slowly in plus power.
  4. Narrower reading area.
  5. Good for first time presbyopes- especially VDU Users.
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18
Q

Describe firm (Super soft) design?

A

Offers larger distance, intermediate and reading area. Ideal for all presbyopes, previous bifocal wearers and those non-tolerant to other PPL designs.

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19
Q

Methods of presenting PAL designs?

A
  1. Iso-cylinder lines
  2. Vector plots
  3. Is0-mean power lines
  4. Just noticeable blur
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20
Q

Iso-cylinder lines show?

A

Regions of equivalent cylinder power

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21
Q

Vector plot shows?

A

The magnitude and direction of astigmatism

22
Q

Iso mean power lines show?

A

Regions of equivalent sphere power

23
Q

Just noticeable blur shows?

A

The regions where px will typically 1st notice blur

24
Q

True or false- progressive lenses have limited area of clear vision?

A

True- for both distance and near.
Head movements required to look around

25
Q

Advise to patients using progressive lenses?

A

Point nose at what they want to look at instead of eyes. To find correct power for a given distance px needs to raise/ lower chin.

26
Q

Adaptation period for progressive lenses?
How to ensure successful adaptation to progressive lenses?

A

2 weeks
Continuous wearing of new progressives

27
Q

How to dispense progressive lenses?

A
  1. Select a correct size and shape of frame.
  2. Adjust frame so it sits straight before taking measurements.
  3. Pantoscopic tilt should be 10 degrees.
  4. Use monocular PDs for distance.
  5. Height of pupil- state if below or above HCL.
  6. Ensure chosen lens will fit into chosen frame.
  7. Shorter corridor lenses are available for pxs that insist on shallow frames
28
Q

Depth of standard lenses from pupil to bottom of lens should be approx?

A

18-20mm

29
Q

PPLs are supplied with 2 types of markings for?

A

Layout, power verification, dispending and identification purposes

30
Q

Alignment reference marking used to?

A

Used to reapply the ink markings and for verifying horizontal alignments

31
Q

Distance reference point used for?

A

Represents the location on the surface that provides the extra base curve, which is the optimal location for verifying the distance Rx.

32
Q

Fitting point or cross represnts?

A

The point of the lens that lies directly infront of the pupil.

33
Q

Prism reference point represents?

A

Position for verifying prescribed prism or prism thinning. It is positioned exactly in-between permanent alignment reference marking.

34
Q

Near reference point represents?

A

Location that provides full add power and is the location for verifying the add power of the RX using focimeter.

35
Q

Manufacturer marking represents?

A

Manufacturer logo and is always below the nasal alignment reference marking.

36
Q

Add on progressive lenses is found at what location?

A

Always below the temporal alignment reference marking.

37
Q

Reading area in hard vs soft design?

A

Reading area is wider in hard design in comparison to soft design.

38
Q

‘Swim’ meaning in relation to progressive lenses?

A

This is the disturbance caused by unwanted astigmatism especially during dynamic vision (objects moving). Leads to distortion of images and px experiences sensation of balance loss.

39
Q

Why is monocular PDs taken when dispensing progressive lenses?

A

Centration of lens is very important- if off by a few mm it results in high cylindrical error and vision will not be clear.

40
Q

What is the solution when accommodation drops so low that px can’t see clearly at intermediate distances? Long term vs short term solution

A

Long term: Use of trifocals or progressive lenses.
Short term: Moving closer to the screen.

41
Q

Minimum fitting height for general purpose progressive lenses?

A

18-20mm (vary between manufacturers)

42
Q

How far apart are engraved horizontal reference markings?

A

34mm apart

43
Q

What do iso-cylinder lines represent?

A

Lines of equal cylindrical power joining.

44
Q

What do vector plot lines represent?

A

Longer vector plot lines indicate a bigger magnitude and the orientation of lines determines the direction of cylinder. HENCE MAGNITUDE AND DIRECTION OF ASTIGMATISM.

45
Q

Can plot/ vectors determine what the px is expected to see?

A

The plots do not determine the vision the px will experience

46
Q

Hard vs soft design- which design has more unwanted surface astigmatism?

A

Soft design has small distance of unwanted astigmatism compared to hard design.

47
Q

Implication of ‘swim’ on pxs?

A

Image through the lens appears to be distorted and some pxs will experience loss of balance.

48
Q

Iso mean power shows?

A

Shows regions of equivalent sphere power

49
Q

Just noticeable blur shows?

A

Shows the regions where px will typically 1st notice blur

50
Q

Cyan (blue dotted lines) indicate?

A

Indicate where astigmatism is low ( <0.50D)

OP2201- Dispensing (7 decks)

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