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Contact lens > GP CLs > Flashcards

GP CLs Flashcards

1
Q

Adherence of a cl increased by:

A
  • increased OZD/TD
  • Decreased BOZR(Steep BC)
  • Decrease peripheral/IM curve radii
  • decrease thickness
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2
Q

Cl adherence decreased by:

A
  • decreased OZD/TD
  • Increased BC
  • Increased thickness
  • increase peripheral/IM curve radii
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3
Q

Capillary attraction

A

F = 1/t

Attraction (F) inversely proportional to tear layer thickness (t)

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4
Q

What is the TFSP

A

Tear fluid squeeze pressure

  • force holding cl in place
  • centres cl by opposin gravity/eyelid force
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5
Q

ELF

A

Holds cl between blinks - -ve pressure counteracts gravity

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6
Q

CoG shifts backwards when:

A

Increased minus power
Increased TD
Decreased bc
Decreased centre thickness

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7
Q

CoG shifts forwards

A

More positive power
Decreased TD
Increased bc
Increased centre thickness

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8
Q

Techniques to promote adaptation

A

Viscous wetting solution
Eye closure 5-10s
Downward gaze in dim room
Refrain from primary gaze

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9
Q

White light static assessment

A

Cl Position post settling
- central/high/low riding/decentred obliquely

Centration - with/without lids

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10
Q

White light dynamic assessment

A

Post blink - recentration
Lateral gaze - cross limbus?
Speed/lag

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11
Q

Importance of static assessment

A

Static only way to confidently make valid comparisons between designs

Dynamic fits affected by:
Gaze direction
Blink force
PAS
lid tension
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12
Q

Static assessment

A 
Centration
Central pooling 
Mid peripheral bearing 
Edge lift on peripheral curve 
Tear exchange
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13
Q

Steep fit

A 
Central pooling
Mid peripheral bearing 
Narrow edge clearance 
Typically unstable - decentres inferiorly 
Little/no movement
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14
Q

Flat fit

A 
Central bearing 
Mid peripheral pooling 
Excessive edge clearance 
Excess movement on blink 
Discomfort / inconsistent vision
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15
Q

How to correct a steep fit

A

Decrease TD
Increase BC
Decrease BOZD
Flatten BPRs

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16
Q

How to correct flat fit

A

Increase TD
Decrease BC
Increase BOZD
steepen BPRs

17
Q

What does the final GP rx consist of

A

BVP trial cl
Tear lens power
Over rx

18
Q

Conditions only fitted with GP

A

Keratoconus
Traumatised corneas
Post graft

19
Q

Benefits of GP

A 
Customisable 
Less contamination risk
Wider range 
Lifestyle issues - eg sports 
Better VA
Less deposit build up
Less surface dehydration
20
Q

GP parameters

A 
TD = HVID -2mm
BC = 0.1 steeper than flattest K or flattest K for high astigmatism (2.50+) (toric BC)
BOZD = scotopic pupil +1mm (min)
21
Q

FAP

A

Flat add plus

Every 0.1mm flatter BC -> O/R with +0.50

22
Q

SAM

A

Steep add minus

For every 0.1mm steeper BC -> O/R with -0.50

23
Q

Px selection for simultaneous GP Mfs

A

Reading position straight ahead
Can read any position - not just down
Early mod presbyopes
IM task demands - computer, music sheets, sewing etc

24
Q

Px selection for translating GP Mfs

A 
Reading position down
Need excellent DV
High adds
Large/small pupils - not pupil dependent
Lower lid within 1mm of limbus
Fair PAS - allow 2mm translation
Sclera flatter than cornea - allow translation
25
Q

Advantages of translating GP Mfs

A

Excellent dv/nv
Normal stereo
Good contrast
Customisable - wide ranges/high adds/choice of materials

26
Q

Disadvantage to translating GP Mfs

A

Need stabilisation - prismballast/truncation
Very mobile - not as comfortable
Bifocal - gaze dependent
- IM portion absent/poor

27
Q

Advantages of simultaneous GP Mfs

A 
Minimal gaze dependence 
Comfort = to SV GP
normal stereo
No jump -prismatic effect
Easier fit than alternating
28
Q

Disadvantages of simultaneous GP Mfs

A 
Difficult to get high adds
- may need over specs/monovision
Compromised VA 
Some contrast loss
Spectacle blur in higher adds 
Not avail in BST design
29
Q

Fix GP Mf low riding

A

Avoid steep fit
Increase TD
Change stabilisation method? - negative carrier for high plus
Avoid high WTR astigmatism >2.50

30
Q

Fix high riding GP Mf

A 
Decrease TD - if narrow PAS
avoid flat fit
Avoid WTR astigmatism 
Avoid excess lid attachment 
Diff cl design - prism ballast
31
Q

Fix laterally decentred GP Mf

A

Increase TD

Avoid mod ATR astigmatism >1.50

32
Q

GP MF - poor DV

A
  • O/R - giving least amount minus
    Reduce add in Dom eye
    Change Dom eye to SV
    Larger zone over which add works - if large pupils
33
Q

GP Mf - poor NV

A

Increase add in non-Dom eye
O/R - if add >0.75 change to FST non Dom eye
Smaller zone over which add works - small pupils

34
Q

Gp Mf rotation

A

Nasal rotation <30deg accepted / >30deg compensate

Any Temporal rotation compensate

35
Q

Assessing GP MF FIT

A

Speed of return: <1s accept / >1s adjust fit (BC)

Seg position: to sit between 20-30% of pupil - if >1/3mm into pupil - adjust (decreasing TD)

Contact lens (8 decks)

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