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CLP > Week 1.11 RGP Contact Lenses > Flashcards

Week 1.11 RGP Contact Lenses Flashcards

1
Q

Some general notes about RGP

A

RGPs have been around lot longer than SiHi
Less commonly fitted compared to SCL
Creates a very loyal px base as generally they are more durable and long lasting and less risk of infection
Custom made lens. Any design/material too

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2
Q

How many curves does a contact lens have

A

Tricurve

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3
Q

What are the measurements needed to fit a RGP lens

A
  • history to ensure RGP wear acceptable/tolerable
  • health check of eye
  • keratometry readings
  • pupil measurements
  • HVID
  • VPA - vertical palpebral aperture - gap between top and bottom lid
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4
Q

What do we need to know for our selection of an initial trial lens

A
  • total diameter
  • BOXR - need to know for curvature of the lens
  • BVP
  • Lens design
  • lens material
  • cost?
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5
Q

Are RGP cheaper than SCL?

A

RGP is cheaper than SCL however initial cost is there aswell

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6
Q

For RGP lens what we want the HVID total diameter to be

A

HVID - 2mm
TD - 9.8mm is perfect

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7
Q

For spherical corneas do we want a larger or smaller fit RGP? And why?

A

For spherical corneas, the larger the RGP the more stable the fit - less movement seen and VA stable

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8
Q

For toric corneas do we want a larger or smaller fit RGP? And why?

A

For toric corneas, a smaller fit may make the fit/vision more stable - doesn’t rock on cornea or spin with blinking as much

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9
Q

How do we know what the BOZR of the lens should be

A

We start by fitting BOZR that is most similar to largest or flattest K

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10
Q

Tear lens and RGPs

A
  • can take advantage of the tears underneath the lens
  • water has a weaker refractive index than the lens but higher than air
  • if we use flattest k we can use tear film to correct astigmatism in some cases
    However cannot always fit RGP on flattest K because at some point, toxicity of cornea may be too much
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11
Q

What is the rule of thumb for keratometry readings to work out the amount of astigmatism regarding keratometry readings NOT rx

A

0.10mm difference in keratometry readings equates to +/-0.50DC

0.05mm difference will therefore be 0.25DC

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12
Q

What would be the approximate BOZR for spherical RGP lenses based on k readings

A

If the astigmatism by keratometer is:

Spherical to 0.74D - fit on flattest k reading
0.50 to 1.00D - fit on flattest k reading to 0.05 steeper than flattest k reading
1.00 to 2.50D - fit near flattest k reading (0.05 to 0.10 steeper at most)
Over 2.50 - toroidal back optic zone is recommended

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13
Q

What BOZR would we need if 7.8 @180 and 7.6@90?

A

7.8 and 7.6 there’s a 0.2mm difference so 1.00DC
7.8 is flattest K so you want 0.05 steeper than 7.8 so 7.75

Value gets smaller so steeper/tighter/smaller

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14
Q

For values over 2.50 astigmatism shown by keratometer readings…

A

… we no longer use spherical RGP lenses as the lens will still rock too much even if we try steepening the flattest K

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15
Q

If u put the lens with flattest k and doesn’t fit with how u expected, improve the fit using the two simple RGP rule:

A

1) flattening (increasing)/ steepening (decreasing) the BPZE by 0.05mm is equivalent to a change in -/+0.25D respectively

2) flattening/steepening the BPZR by 0.05mm requires an increase/decrease of 0.5mm to BOZD

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16
Q

BOZD

A

The diameter of the initial central curvatures that contains corrective power

Important that it is larger than max pupil size (measured in dark light)
- usually approx 0.7mm larger than pupil diameter

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17
Q

What about peripheral curves

A
  • often predetermined by manufacturer
  • first curve is 0.7mm flatter than BOZR
  • final curve is approx 10.50mm
  • If you make it flatter u get less corneal irritation but might irritate the lids
  • too little peripheral clearance causes poor tear exchange
  • too much will make your lens unstable
18
Q

When do we need to correct for back vertex distance

A
  • greater than -/+4.00D
19
Q

If spec rx is -3/00/0.75x180 what’s the BVP and do we need to do anything to correct the astigmatism

A

BVP is -3.00DS
Table indicates flattest k, fluid lens will correct the -0.75DC

20
Q
  • If spec rx is -4.00/-1.25x90
    What’s BVP and flattest k
A

BVP is -4.00
Table indicates fitting 0.05mm steeper BOZR than flattest k, fluid will correct the -1.25DC

21
Q

What is the suffix given to all RGPs

A

-focon

22
Q

What’s the suffix given to soft lenses

A

-filcon

23
Q

Is all astigmatism corneal?

A

No some is lenticular astigmatism so u need to know px rx as well as keratometry readings.

24
Q

7.70@180
7.00@90
Rx: -3.00/-1.00x180
What’s the amount of astigmatism

A

In the cornea:
- 7.70 and 7.00 that’s a 0.70 difference so 0.50x7=3.50D
So most steep should be at 90 (because astigmatism here is at 90) which is as 7.00@90

25
Q

When would we need to foot a toric lens

A

If the corneal astigmatism is too high >2.00D
Or if the majority of the cyl correction is not corneal

26
Q

What are the 3 types of toric RGP lenses

A

Front surface toric
Back surface toric
Bitoric lens

27
Q

Why would a front toric be a bad choice for corneal astigmatism?

A

Doubled he amount of astigmatism as the font surface is corrected astigmatism but there’s also the tear lens which is corrected - too much correction

28
Q

Why would a back surface toric be a bad choice for lenticular astigmatism

A

Spherical cornea so lens wouldnt fit nicely

29
Q

Which topics are good for corneal astigmatism and which for lenticular

A

Back surface torics good for corneal astigmatism
Front surface toric good for lenticular astigmatism

30
Q

What is the way to write out the specification of the RGP lenses

A

Manufacturer: design: BOZR/TD/BVP: material: tint: engraving

31
Q

How to conduct the fit assessment of an RGP - brief overview

A
  • RGPs come dry from manufacturer
  • Ensure lens is wet and sterile before insertion – may be dry in a trial bank so ensure u wet them with correct wetting solution
  • RGPs will cause lacrimation and therefore some adaptation time is required for the patient to allow the lens to settle before you can assess the fit
  • The conduct a white light assessment
  • Then conduct a fluorescein assessment
    o This is different to SCL fit – NaFL goes in with the lens
  • You should aim to comment on at least 8 features of the fit in order to accurately summarise the fit (I.e. steep or flat or possibly alignment)
    o No longer use the word tight and loose
32
Q

White light assessment for RGPs

A
  • medium mag
  • broad beam
  • check how the fit is in relation to the
    1) centration - is it central diodes it drop down or stuck in place central H/V?
    2) MOB - does it move a lot? (Will move more than SCL as its smaller 1.5mm movement)
    3) how does it move - in a pattern?
    4) coverage - covers entire pupil to ensure good VA?
    5) lag/limbus - whether the lens crosses the limbus with excursions - record as ‘within limbus on excursions’
    6) lid interaction - does it move with the lid/ lid attached? Does it move freely without too much lid involvement?
    7) wettability and deposits - any patches of dryness?
33
Q

What is one assessment technique used in SCL assessment but not RGP

A

Push up test is NEVER performed with RGP lenses

34
Q

How to do Fluorescein assessment of RGP lens

A

After white light assessment
Check the edge lift
Fluorescein pattern - central pooling? Air bubbles?

35
Q

What Fluorescein pattern will u see in a steep RGP fit

A

Central pooling
Trapped air bubbles

36
Q

What Fluorescein pattern will you see in a flat RGP lens

A

Central touch
Lots of fluorescein on outer areas
Excessive movement

37
Q

What pattern does toric corneas with spherical RGP make in fluorescein assessment

A

Dumbbell pattern

38
Q

Do u do over refraction in RGP

A

Yes use the rule:
Change in fit of 0.05mm will give change in over refraction of 0.25D

39
Q

Do u do over refraction in RGP

A

Yes use the rule:
Change in got of 0.05mm will give change in over refraction of 0.25D

40
Q

When should I choose RGP lenses

A

New wearers 16/24 7/7
Corneal cyl over 1.00DC
Irregular cornea
Dry eye
Dry environment
High permeability required
History of allergies
Dilated limbal vessels
Poor compliance with SCL
Financially challenged px

Refits and soft failures
- poor variable VA in SCL
- dry eye sxs with SCL
- poor SCL centration
- poor handling
- corneal vascularisation - considered sihi
- repeated infection
- SCL deposition
- solution or material allergy

41
Q

What are the benefits of RGP lenses

A
  • crisp vision
  • stable vision
  • easy to handle
  • lower levels of complications
  • cost effective
  • good long term comfort
  • profitable

CLP (3 decks)

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