Dispensing 5 - Non Tolerance

Question 1

what is lens non-tolerance?

Answer 1

intolerance to a particular lens type, material, lens form or prescription

Question 2

what is the difference between lens non-tolerance and psychological non-tolerance?

Answer 2

lens non tolerance is an actual intolerance to an aspect of the lens whereas psychological is where the symptoms are irregular and fail to fit any pattern hence there is not usually a physical problem more the problem is due to how the patient feels

Question 3

what are potential reasons for psychological non-tolerance?

Answer 3

-patient feels like they were forced into the purchase
-realised they didnt want to spend that much for their glasses
-changed their mind about the style of frame chosen
-third party made an unfavourable comment about their new specs
-spectacle lens solution chosen does not fit into patient’s lifestyle
-spectacles fail to meet the pxs expectations

Question 4

what are two types of non tolerance?

Answer 4

lens and psychological

Question 5

how do you prevent either form of non-tolerance

Answer 5

-carefully consider optical, functional and cosmetic properties of the spectacles
-carefully consider any changes recommended compared to the pxs previous spectacles
-take a methodical problem solving approach

Question 6

what is the general order or steps when dealing with a non tolerance case in single vision spectacles?

Answer 6

1. focimeter and confirm sphere/cyl/axis
2. Focimeter and confirm prism (ground in or intentional/unintentional shift in
   optical centre)
3. Compare base curve (use a lens clock)
4. check coatings and tints
5. check frame fitting
6. consider px adaptation times/ educate on how to use their lenses
7. recheck considering cycloplegic refraction, any change in cylinder and pathological refractive change (e.g. cataract)

Question 7

what is the general order or steps when dealing with a non tolerance case in bifocals?

Answer 7

1. focimeter and confirm sphere/cyl/axis
2. Focimeter and confirm prism (ground in or intentional/unintentional shift in
   optical centre)
3. Compare base curve (use a lens clock)
4. check near add power and whether it is sufficient for the patient’s requirements
5. check fitting in relation to segment height and inset and check segment choice
6. check coatings and tints
7. check frame fitting
8. consider px adaptation times/ educate on how to use their lenses
9. recheck considering cycloplegic refraction, any change in cylinder and pathological refractive change (e.g. cataract)

Question 8

what is the general order or steps when dealing with a non tolerance case in progressives?

Answer 8

1. focimeter and confirm sphere/cyl/axis
2. Focimeter and confirm prism (ground in or intentional/unintentional shift in
   optical centre)
3. Compare base curve (use a lens clock)
4. check near add power and whether it is sufficient for the patient’s requirements
5. check frame depth to ensure patient can achieve the maximum add and check fitting (fitting cross heights and mono pds) and choice of lens design
6. check coatings and tints
7. check frame fitting
8. consider px adaptation times/ educate on how to use their lenses
9. recheck considering cycloplegic refraction, any change in cylinder and pathological refractive change (e.g. cataract)

Question 9

what could cause single vision non-tolerance assuming the Rx is correct?

Answer 9

o Optical centration errors
o Changes in lens form and/or material
o Incorrect frame fitting or inappropriate frame selection
o Cosmesis
o changing the lens from spherical to aspherical or vice versa
o changes in base curve
o spec mag
o material
o eye size

Question 10

What could cause optical centration errors in non tolerance lenses?

Answer 10

-unwanted prismatic effect
-Binocular fusion system has a greater tolerance for horizontal errors than vertical errors.
-if they need prism/ have the wrong prism D
-calculating differential prismatic effect
-patient not having had enough time to adapt

Question 11

how can unwanted prismatic effect cause optical centration error?

Answer 11

As prism increases with error in centration/ power of the lenses

Question 12

What’ s the difference between horizontally mis-centred lenses and vertically mis-centred lenses?

Answer 12

Horizontally mis-centred lenses can cause the visual system to become
stressed over a period of time whereas vertically mis-centred lenses can cause the visual system to be stressed immediately

Question 13

according to Tunnacliffe and Williams (1985) what did they say to compare how photopic conditions and mesopic conditions affect visual function?

Answer 13

“In photopic conditions one prism-dioptre causes a significant drop in sensitivity at all spatial frequencies and in mesopic conditions as
little as a half prism-dioptre has a similar effect.”

Question 14

what is a common change in lens form?

Answer 14

spherical to aspherical lenses?

Question 15

why does changing from spherical to aspherical lenses cause lens - intolerance?

Answer 15

because, a wearer that has adapted to the off-axis performance of a spherical lens will often find the
sudden correction of the off axis when they are switched to an aspheric lens form (or vice versa) difficult to adapt to

Question 16

how can changes in base curve cause single vision non-tolerance?

Answer 16

Steeper base curves (6 to 8 base) such as those found in many wraparound style sunglass lenses can also lead to intolerance as the spec mag and off axis vision can be hard to adapt to

Question 17

how can you summarise the formula for spectacle magnification (SM)

Answer 17

the product of the shape
factor [ 1 / (1 - (t/n * F1) ) ] and power factor [ 1 / (1 – (d * Fv) ) ] where:
o t = centre thickness
o d = BVD
o Fv = BVP
o F1 = front surface power

Question 18

what variables affect the degree of spectacle magnification?

Answer 18

-centre thickness
-bvd
-bvp
-front surface power

Question 19

for spectacle magnification, what symptoms may Px complain about and why? what do you need to tell the patient

Answer 19

-objects such as the ground appear closer or further away,
although many patients do eventually adapt to this change.
-as SM of a lens directly affects retinal image size
- is important to
emphasise the need for patience while the adaptation process occurs.

Question 20

why may anisometropic patients be non-tolerant to SM?

Answer 20

because a change in the relative image sizes between the right
and left eyes may lead to a breakdown in binocular fusion

Question 21

how can changes in material cause single vision non-tolerance?

Answer 21

because changes in refractive index may give rise to complaints ranging from a lack of clearly defined sharpness to colour fringing around high contrast objects and blur around low contrast objects so careful consideration of the v-values when comparing suitable lenses and by discussing the period of adaptation often required.

Question 22

why can eye size cause single vision non-tolerance?

Answer 22

because the larger the eye size, the greater the oblique astigmatism causing symptoms of clear central vision and increasing degrees of blur and disorientation as oblique
gaze increases

Question 23

what are symptoms of incorrect frame?

Answer 23

poor comfort, contact marks and constant slipping

Question 24

why can incorrect frame fitting cause lens non-tolerance?

Answer 24

because initial symptoms can be fixed with adjustments but failure to consider any vertex distance adjustment can result in an over or under correction of the final lens power

Question 25

how are symptoms on inappropriate frame selection different to incorrect frame fit?

Answer 25

complaint is normally more
to do with the function of the frame rather than its fit or comfort

Question 26

what variables on the frame can vertex distance depend on?

Answer 26

-pantoscopic tilt
-pad angles
-head width
-temple width
-length to bend

Question 27

what kind of prescriptions does vertex distance of a frame have most effect on?

Answer 27

prescriptions of ±5.00D

Question 28

give 4 common cosmesis symptoms

Answer 28

o The lenses are thicker than the patient expected
o The tint is not what the patient expected
o The frame colour doesn’t suit them
o The frame style doesn’t suit them

Question 29

what are specific bifocal non tolerance causes?

Answer 29

o Jump
o A reduced field of view when reading
o The segment inappropriately placed
o Unsatisfactory intermediate vision
o Changes in segment type from a round to flat-top design or vice versa will affect the prismatic effect experienced at the near visual point and thus alter the relative
position of objects viewed through the reading segment.

Question 30

how can the way bifocals are designed, reduce non tolerance?

Answer 30

-flat top design in minus lenses
-round design in plus lenses
means some of the prism created by the main lens when the wearer glances down is neutralised

Question 31

in bifocals, give symptoms of non-tolerance due to a change in segment type

Answer 31

-inability to walk up and down stairs with the new spectacles
-disorientation when glancing down through the segment margin

Question 32

how can you reduce non-tolerance when dispensing bifocals?

Answer 32

-px who already wear bifocals make sure segment size and position should be matched to their previously worn bifocal lenses
-new patients should be establish patient’s expectations in
respect of their use of the spectacles for near, distance and intermediate vision

Question 33

give 5 common solutions for anisometropia in bifocals

Answer 33

o Different diameter round segment bifocals
o Split bifocals
o Prism-controlled bifocals
o Cemented or bonded bifocal segments
o Slab on/slab off

Question 34

what are specific causes of progressive lens non-tolerance?

Answer 34

o Ineffective instruction as to their use
o Inappropriate change in design of progressive
o Inappropriate lens design
o Incorrect positioning

Question 35

how can you avoid unnecessary changes in lens brand/lens design which could lead to progressive lens non-tolerance?

Answer 35

-make sure to properly discuss patient’s lifestyle, hobbies and occupation
-dont change it if px is already happy with current design
-discuss how changes in lens design can mean px will need to adapt

Question 36

in progressive lenses, how can you achieve a shorter corridor?

Answer 36

compress the intermediate and
near zones, leaving the distance area unchanged

Question 37

when may a short corridor progressive lens design cause non tolerance? what are the symptoms of this?

Answer 37

-For both new and existing wearers that require a good field of view for intermediate or close work
symptoms:
-an inability to view a computer screen
-complaints that they can only read through a tiny portion of the lens

Question 38

What is the maximum vertical DPE should be expected to tolerate over long periods of time

Answer 38

1 prism diopter