4. Non- tolerance

Question 1

Lens non-tolerance meaning?

Answer 1

Intolerance to a particular lens type, material, lens form or Rx.

Question 2

Physiological non-tolerance meaning?

Answer 2

Irregular symptoms that fail to fit any pattern. Apparent determination to simply ‘not get on’ with the new specs.

Question 3

If Px is physiologically rejecting the specs, how to eliminate actual lens intolerance?

Answer 3

Adopt a diplomatic approach to finding a mutually acceptable solution. Vital to retain Px confidence.

Question 4

2 types of non-tolerance?

Answer 4

Lens and psychological

Question 5

Single vision lenses with correct RX, what other factors can cause single vision non-tolerance?

Answer 5

1. Optical centration errors
2. Change in lens form or material
3. Incorrect frame fitting
4. Cosmesis

Question 6

Optical centration error results in?

Answer 6

Unwanted prismatic effect- Prism increases with errors in centration or power of lens.

Question 7

Binocular fusion system has getter tolerance for horizontal or vertical errors?

Answer 7

Horizontal

Question 8

Impact of horizontal vs vertical mis-centered lenses?

Answer 8

Horizontal mis-centered les cause stress to visual system over a period of time. Vertical mis- centered lens cause immediate stress to the visual system.

Question 9

2 ways of confirming prism in a lens?

Answer 9

1. Mark optical centers with focimeter using marking tools and ask px to wear the lens and see if px is looking through the optical centers.
2. Mark px pupils on the lens when worn then focimeter through those points to read off the prism.

Question 10

Change in base curve from what px was using before can lead to?

Answer 10

Can lead to distortions

Question 11

How is lens fitting checked?
Single and bifocal lenses

Answer 11

Single visions: Is lens pitching on nose, uncomfortable, red marks, pads need adjustment?
Bifocals: Check add power- sufficient? Check fitting (seg height, choice and inset)

Question 12

How is lens fitting checked- Progressive lenses?

Answer 12

Is near power sufficient?
Check frame depth- to ensure px has maximum add.
Check frame fitting- fitting cross heights, mono PDs and lens design

Question 13

How much vertical mis-centration is not tolerated by the eyes?

Answer 13

Not more than 1 diopter over a long period of time.

Question 14

Aspherical lenses pose a get risk of?

Answer 14

Potential single vision lens intolerance

Question 15

What factors affect spectacle magnification (SM)?

Answer 15

Surface power, lens thickness and refractive index

Question 16

Spectacle magnification (SM) directly affects?

Answer 16

Retinal Image Size

Question 17

In anisometropic px’s change in relative image size between RE & LE leads to?

Answer 17

Leads to breakdown in binocular fusion and non-tolerance

Question 18

Change in material- px will complain of?

Answer 18

Lack of clearly & defined sharpness to colour fringing around high contrast objects and blur for low contrast objects

Question 19

How is v value picked?

Answer 19

Comparing suitable lenses and by discussing the period of adaptation required.

Question 20

Pxs vision through a lens is perfect, but they still complain of poor comfort or frame keeps slipping/ contact marks, why?

Answer 20

Incorrect frame fitting or inappropriate frame selection

Question 21

Failure to consider any vertex distance results in?

Answer 21

Over or under correction of final lens power

Question 22

Vertex distance depends on?

Answer 22

Pantoscopic tilt, pad angles, head width, temple width and length

Question 23

Adjusting pantoscopic tilt can make small adjustments in?

Answer 23

Small adjustments in vertical positioning of optical centres

Question 24

Symptoms of bifocal non-tolerance

Answer 24

1. Jump
2. Reduced field of view when reading
3. Segment inappropriately placed
4. Unsatisfactory intermediate vision

Question 25

Benefit of flat-top design in minus lenses and round designs in plus lenses?

Answer 25

Neutralizing some prism created by the main lens when wearer glances downwards.

Question 26

How to reduce non-tolerance in Px’s that previously wore bifocals?

Answer 26

Examine previous bifocals worn by Px- seg size and position should be the same as previous lenses.

Question 27

Non-tolerance in anisometropic patients?

Answer 27

Issue of differential prism- if this is not resolved at near vision point risk of intolerance

Question 28

Non-tolerance in anisometropic patients solutions?

Answer 28

1. Different diameter round segment bifocals
2. Split bifocals
3. Prism controlled bifocals
4. Cemented or boned bifocal segments
5. Slab on/ slab off

Question 29

How is TCA calculated?

Answer 29

TCA = p/V (p =cF)

Question 30

What is constringence?

Answer 30

Abbe number/ v value

Question 31

What axis is considered when calculating vertical DPE?

Answer 31

Value along 90 meridian

Question 32

When is TCA value a reason for concern?

Answer 32

When TCA > 0.1. Px likely to notice the effects

Question 33

Relationship between refractive index and v value?

Answer 33

As refractive index increases, v value decreases.

Question 34

What is required to calculate jump?

Answer 34

Radius in cm
Add power
And ans will be BD (because jump causes image to move up)

Question 35

What is anisometropia? S

Answer 35

Significant difference in Rx between both eyes