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Contact lenses year 3 > Presbyopic contact lens fitting > Flashcards

Presbyopic contact lens fitting Flashcards

1
Q

list 5 ocular structures that you need to take into consideration which can change with age when wanting to fit presbyopic contact lenses

A
  • Eyelids
  • Cornea
  • Tear film
  • Conjunctiva
  • Pupils
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2
Q

list 3 ageing changes that can occur with the eyelids

A
  • Reduced elasticity (reduced muscle tonus)
  • Atrophy of orbital fat
  • Change in position of eyelids e.g. ectropion, entropion, ptosis
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3
Q

why can’t you fit a patient who has ectropion with contact lenses

A

there is no lubrication so the eyes will dry out - if you put flourescein will see staining at the bottom, the same will happen to the CL

eyelid affects the lens stability

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4
Q

list 5 ageing changes that can occur with the cornea

A
  • Decreased corneal sensitivity
  • Age related corneal degenerations
  • Corneal aberratiosn increases-also pupil size changes and lens changes
  • Corneal curvature changes (astigmatism will change and affects multifocal fitting)
  • Changes to all layers of cornea including epithelial, stromal and endothelial changes
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5
Q

list 2 ageing changes that can occur with the tear film

and 5 intrinsic factors that cause these changes

A
  • Decrease in tear production
  • Decrease in tear stability
    = CL will get dry

Intrinsic factors:

  • Decrease in conjunctival goblet cell density = less mucous production
  • Change in meibomian gland secretions = less lipid produced
  • Lid changes- affect tear film e.g. blinking
  • Changes to lacrimal ducts and gland
  • Change in tear osmolarity
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6
Q

what systemic ageing factors can cause dry eye

A
  • medications a px takes e.g. hormone replacement therapy

- older px also have more systemic conditions which can also cause dry eye e.g. arthritis

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7
Q

list 2 ageing changes that can occur with the conjunctiva

when can they not be too much of a problem
what can be taken to help with any symptoms

A
  • Pterygium
  • Pingueculae

if these are of low grade then they don’t tend to affect CLs to much and a soft lens can just wrap around that
these px may sometimes need artificial tears

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8
Q

list 2 ageing changes that can occur with the pupils

A
  • More miotic with age, ‘senile miosis
  • Weakening of iris radial dilator muscles

some designs of CL required pupil to change

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9
Q

list 3 types of presbyopic CL options available

A
  • over spectacles
  • multifocal CLs
  • monovision
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10
Q

how are over spectacles CLs used

A
  • Full distance correction CLs
  • near ADD specs on top of CLs to read
    (but blurred when looking up for distance)
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11
Q

list 3 advantages to over spectacles CLs

A
  • No difference to cost, px may continue to use existing brand of CLs (if fit etc is adequate)
  • Allows stable distance vision (no fluctuation)
  • Simple, inexpensive, easy to use
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12
Q

list 2 disadvantages to over spectacle CLs

A
  • Still need specs to see, therefore might be inconvenient

- Use of specs negates some of the cosmetic benefits provided by CL wear

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13
Q

why are ready readers not an ideal option of glasses to use for over spectacle CLs

A

because they are no good for concentration tasks and long reading times as the PD’s are set and this can cause prismatic effect if the PD is not centred

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14
Q

how is a mono vision CL used

A
  • Patient wear single vision contact lenses
  • Other (non-dominant) eye has reading prescription added to distance rx.
  • One eye (the dominant eye) is fully corrected for the distance
sometimes you dont have to give the whole reading add and can just give partial add for better tolerance 
e.g.
-3.00D px with a +1.00 ADD 
= 
-3.00D in dominant eye 
-2.00D in non-dominant eye
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15
Q

which type of add will a mono vision CL work well for and not work well for and why

A
  • may work well for low adds
  • may not work well for higher reading adds ~+2.50D i.e. older presbyopes
    because:
    +2.50D is the limit to the amount of difference between the 2 eyes that can be tolerated
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16
Q

list 5 advantages of using mono vision CLs

A
  • No increase in cost
  • No change in lens type, only lens power (so don’t need to do a new fit)
  • Wider range of lens material options as using single vision lenses
  • Useful for existing wearers
  • Easy for practitioner to fit = high success rate
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17
Q

list 6 disadvantages of using mono vision CLs

A
  • Loss of stereopsis
  • Loss of contrast - as with many multifocal corrections
  • Adaptation required – as with all multifocal options
  • Cannot be used with px who are monocular
  • Px must have strong ocular dominance
  • Not suitable for a patient with strong near visual task demands
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18
Q

what causes the loss of stereopsis with mono vision CLs

A

because the eyes are receiving different images, one corrected for distance and one corrected for near.
so is no good for driving

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19
Q

how are multifocal CLs classified

A
  • RGP:
  • alternating or simultaneous
  • alternating: solid or fused
  • simultaneous: aspheric
  • Soft:
  • alternating or simultaneous
  • alternating
  • simultaneous: multi-zone or zonal aspheric or aspheric
  • aspheric: centre near or centre distance
20
Q

how does a alternating sign (translating) multifocal CL work

A

Two distinct sectors - just like a bifocal lens

  • Patient looks out of the distance portion, this is located at the top of the lens
  • On down gaze, the upper eyelid holds the lens in place and patient looks out of lower portion for reading/near vision. Some texts state that the lens must move up on downward gaze to bring near portion of lens into pupil area
21
Q

what 3 conditions are there for fitting a alternating design (translating) multifocal CL

A
  • Lower eye lid should be no lower than the inferior limbus- this helps support lens
  • If lens moves a lot during blinking, the incorrect portion of lens may be moved into the pupil region, this would cause blur
  • Rule of thumb: approx ¾ of pupil region must be covered by the correct section of lens for successful wear at the correct time
    e. g. for distance viewing, 3/4 of the pupil must be covered by the top seg and for near viewing the same applies with the bottom seg
22
Q

list 3 advantages of a alternating design (translating) multifocal CL

A
  • Binocularity (no loss of stereo)
  • Good visual quality
  • Stereopsis should be unaffected
23
Q

list 4 disadvantages of a alternating design (translating) multifocal CL

A
  • Lens stability is important and relies on lens-eyelid interaction. Need lens to move
  • Px who read at eye level or higher (e.g. professions such as plumbers who need to do near tasks but are looking above is no good as lens moves along with eye wherever you look)
  • Adaptation required (won’t know straight away how its going to work out)
24
Q

what are the 2 types of RGP alternating lens
which out of these 2 are usually thinner
what different designs are RGP alternating lenses available in

A
  • solid and fused
  • fused usually thinner
  • different segment sizes available
25
Q

what is 2 advantages of RGP alternating lenses

A
  • RGP MF lenses allow more flexibility as they are easier to customise (so allows for more control with parameters)
  • Plus all the usual benefits of RGPs e.g. correction of astigmatism
26
Q

what are the 3 conditions for a alternating design (translating) fused segmented bifocal lens to work

A
  • On downward gaze, lens should be lifted by at least 2mm
  • In normal lighting, the top of the segment should be level with or slightly below the inferior pupil margin
  • Lens needs to be stabilised e.g. using prism ballast, or truncation
27
Q

how will you troubleshoot for a alternating design (translating) fused segmented bifocal lens if:
Its a high riding lens?
the segment is too high?
px has very low lower lids?

A
  • Try increasing prism and centre thickness to bring lens down
  • Increase truncation to bring lens down
  • Avoid fitting px with these lenses (don’t fit a px with ptosis or ectropion)
28
Q

how is a alternating design (translating) solid segmented bifocal lens designed

how is it fitted

name an example of this lens design

what seg shape varieties are there of this design of lens

other than bifocal, what other translating design RGP lens can you get

A
  • One-piece hard bifocal
  • Bit like an executive spec bifocal
  • Usually fitted so sits a little lower, flatter fit
  • e.g. Tangent Streak lens
  • Flat across or crescent shaped seg
  • a trifocal translating design RGP lens
29
Q

what is the most popular design of multifocal CL

A

simultaneous design

30
Q

how does a simultaneous design multifocal CL work and what advantage does this have

A

Two images placed simultaneously on the retina and the brain picks the one for the right job e.g. for distance or near

Does not rely on lens movement

31
Q

list the 3 types of simultaneous design soft lens subcategories available and which manufacturer they are available from

A
  • Aspheric design
  • Multizone
  • Zonal aspheric

All available from J and J

32
Q

how does a aspheric type of the simultaneous design soft lens work and how is it fitted

A

centre distance:

  • central part used for distance
  • near powered surround
  • difference is due to the use of a back surface aspheric curve

centre near:

  • central part used for near
  • distance powered surround
  • difference is due to the use of a back surface aspheric curve
  • fit the centre-distance in the dominant eye and the centre-near in the non-dominant eye
33
Q

what affect does low and high illumination have on the centre-near lens in the aspheric type of the simultaneous design soft lens and hence what has an affect on these lenses

A
  • Low illumination = larger pupil = distance VA favoured
  • High illumination = smaller pupil = near VA favoured

lighting conditions can have an affect especially for those who work in different lighting conditions

34
Q

list 2 advantages of the aspheric type of the simultaneous design soft lens

A
  • Does not rely on lens movement (so don’t need to worry about lid position)
  • Stereo acuity
35
Q

list 4 disadvantages of the aspheric type of the simultaneous design soft lens

A
  • Dependence on pupil size
  • Adaptation required
  • Lens centration critical otherwise effects such as ghosting can occur
  • Loss of contrast sensitivity
36
Q

list 3 things that need to be considered with the simultaneous design soft lens

A
  • Consider the implications for older px with senile miosis
  • Lens movement - don’t want too much
  • Centration is important (if moves in the eye = can look through wrong bit)
37
Q

how is a multi zone type of multifocal soft CL designed and what advantages does this have over the simultaneous design

A
  • Increase the number of concentric zones powered for D and N alternately
  • Centre-distance multizone design
  • Brain will pick up on the right image

Advantages over simultaneous design:

  • Reduced reliance on pupil size
  • To enable good function in different lighting conditions
38
Q

how is a zonal aspheric type of multifocal soft CL designed

A
  • Uses principles of aspheric and multi zone lenses
  • Zone distribution for each add power (high, med, low) is optimised for the normal physiological change in pupil size that occurs with age
39
Q

what range of ADD is available in the zonal aspheric design of multifocal soft CL

A

+0.75 - +2.50

40
Q

How is a RGP simultaneous multifocal lens designed and which 2 lens types are available

what type do we mostly prescribe

how is this multifocal type of aspheric different to a single vision aspheric lens

what is the principle of this design of multifocal simultaneous aspheric lens

A
  • Designed as aspheric multifocal lenses
  • Front surface aspheric: C-D or C-N
  • Back surface aspheric: C-D
  • We mostly prescribe back surface aspherics
  • Degree of flattening in periphery is much greater than for a SV aspheric
  • The higher the e-value, the greater the + power generated in the periphery…enhancing near VA
    (the higher the degree of flattening in the periphery, the higher the near add = you get that same centre distance effect)
41
Q

list 3 alternatives of presbyopic contact lenses

A
  • Enhanced monovision
  • Partial monovision
  • Modified mono vision
42
Q

what is a enhanced mono vision CL

A

Monovision with DV corrected in dominant eye and a bifocal lens in the non-dominant eye

43
Q

what is a partial mono vision CL

A

When full near correction isn’t incorporated into the non-dominant eye, only a partial correction used
(minimum add required in non-dominant eye, to keep vision fairly ok because will prescribe px binocularly, so don’t give full add)

still correct px for distance in the dominant eye

44
Q

what is a modified mono vision CL

A

Dominant eye = C-D design
Non-dominant eye = C-N design

(used by various manufacturers)

45
Q

list 7 very important considerations you need to make/think about when fitting a presbyopic CL

A
  • History and symptoms, particular attention to occupation and hobbies
  • Consider the patient’s expectations - it will be a compromise, so don’t guarantee for satisfaction and inform px it won’t be fully clear
  • Refractive error – distance and near
  • Check sight test records for presence of other ocular conditions e.g. cataracts
  • Pupil size - think about lighting and how that might affect pupil size
  • Glare? Related to lens design, lens movement, pupil size
  • Checking contrast sensitivity - a test which is often missed, but is useful when fitting MF lenses or resolving MF lens issues
  • Lens centration is critical to most designs
46
Q

what type of sensitivity does multifocal lenses affect and how can you measure the correlation with the success of the contact lens

A
  • contrast sensitivity

- get px to read off the pelli-robosn chart, as this will correlate with the success of the contact lens

47
Q

what are the different ways of determining your dominant eye

A
  • Can use a hole in piece of card or ask px to make a triangle at arms length.
  • Practitioner watches which eye the triangle is moved towards, px will tend to keep dominant eye central
  • Px fixates on a distant target and gradually brings triangle closer to their eyes, maintaining the target in the centre of the triangle

or

  • Extend both hands forward of your body and place the hands together making a small triangle (approximately 1/2 to 3/4 inch per side) between your thumbs and the first knuckle
  • With both eyes open, look through the triangle and center something such as a doorknob in the triangle.
  • Close your left eye. If the object remains in view, you are right eye dominant. If closing your right eye keeps the object in view, you are left eye dominant

or

Use a defocussing lens:

  • Correct patient for distance and ask them to fixate a distant target - Present a plus powered lens (~+2.00) unilaterally. Alternate presentation of lens between the eyes
  • Ask the patient when the letters on the distance chart appear worse
  • The letters will appear less blurred when lens is presented in front of the non-dominant eye, most blurred when the lens is in front of the dominant eye

Contact lenses year 3 (15 decks)

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