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RGP Lenses Flashcards

1
Q

What parameters are needed for ordering RGP lenses? (7)

A
  • Prescription & BVD
  • Keratometry
  • HVID (lens is 2mm less)
  • Lid position
  • Pupil diameter (dim and light)
  • Tear film assessment
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2
Q

What are the indicators of fitting RGP lenses? (5)

A
  • High cylinders
  • Irregular astigmatism like keratoconus
  • Lasts longer than soft CLs (cost efficient)
  • Vision quality is better
  • Creates a tear film and helps to mask corneal astigmatism
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3
Q

What are the contraindications of RGP lenses? (4)

A
  • Interaction from the lids cause discomfort
  • Takes longer to adapt than soft lenses
  • More susceptible to particles behind the lens (dust)
  • Not good for sports as the lens can call out due to loss in elasticity
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4
Q

How do you choose an RGP lens parameters? (3)

A
  • BOZR to match flattest K reading (highest value)
  • Total lens diameter = HVID - 2
  • Spherical component of rx corrected with BVD accounted for
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5
Q

When could you order a tri-curve RGP lens?

A

When corneal astigmatism is approximately 1.50D - the BOZR would be the flattest K reading (highest value) - 0.05-0.10mm

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6
Q

If the pupil is large (7mm) then what diameter RGP lens would need fitting and how will this affect the BOZR?

A

You want the BOZD to be 1-2mm larger than the pupil but increasing the diameter would mean the lens fits steeper. You need to flatten the BOZR to ensure optimum fitting.

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7
Q

How does the thickness of a +4.00D lens differ from a -4.00D lens? How will this affect the fitting?

A

Thick positive lenses = centre of gravity at corneal apex, therefore lens will ride low - FIT LENS STEEPER

Thick negative lenses = centre of gravity is behind, therefore, if too thick then lens will be lifted high due to the lids - FIT FLATTER

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8
Q

Describe the dynamic fit (white light) assessment of an RGP lens and what needs to be recorded (6)

A
  • Centration in primary gaze (horizontal and vertical decentration in mm)
  • Movement on blink (mm)
  • Type of movement (Smooth/jerky/apical rotation)
  • Speed of movement (Fast/moderate/slow)
  • Direction of movement
  • Stability / Lid attachment
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9
Q

Describe the static fit (Fluorescein and cobalt light) assessment of an RGP lens and what needs to be recorded (3)

A
  • Central (Pooling = steep ; Touch = flat)
  • Mid-peripheral
  • Edge (0.5mm = Ideal ; thin = steep fitting as less edge lift ; thick = flat fitting as excessive edge clearance)
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10
Q

What is the lower of the liquid lens if:

1) Flat fitting lens
2) Steep fitting lens

A

1) Negative

2) Positive

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11
Q

How would you change an RGP lens if it is too:

1) Flat
2) Steep

A

1) Tear lens = negative ; ↓ BOZR and ↑ BVP or ↑ TD

2) Tear lens = positive ; ↑ BOZR and ↓ BVP or ↓ TD

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12
Q

When making changes to fitting of an RGP, how much should you change:

1) TD by
2) BC by

A

1) 0.4mm

2) 0.1mm

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13
Q

What are the advantages (4) and disadvantages (3) of aspheric RGP lens designs?

A

Adv:

  • Follows the contour of the cornea
  • Reduced edge clearance = more comfortable as less lid interaction
  • Less pupil dependent so reduces glare and flare
  • If diameter is changed you don’t also need to change BOZR

Disadv:

  • Poor centration
  • Difficult to manufacture
  • Cannot modify
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14
Q

What are the advantages of tri-curve RGP lens designs? (2)

A
  • More control in terms of being able to change parameters

- Minimises lens flexure = more comfort

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15
Q

What are the advantages (5) and disadvantages (2) of a spherical RGP lens design?

A

Adv:

  • Peripheral curves can be altered to optimise fit
  • Good circulation of tears beneath lens
  • Supports tear meniscus
  • Maintains good lid-lens relationship to promote normal blink pattern and comfort
  • Easier to remove lenses

Disadv:

  • Does not follow contour of cornea
  • More pupil dependent
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16
Q

Advantage (1) and disadvantages (2) of PMMA as a RGP lens material

A
  • Optically good and durable
  • Does not allow enough oxygen through
  • Not ocular health friendly
17
Q

Advantages (5) and disadvantages (3) of silicone acrylate as a RGP lens material

A
  • Good range of materials available
  • Good scratch resistance
  • Good vision with limited lens flexure
  • Good dimensional stability
  • Low to medium Dk available
  • 3 and 9 o’clock staining
  • Attracts proteins from tears
  • Some materials are fragile with a breakage problem
18
Q

What does the fluorine atom in fluorosilicone acrylate RGP lenses provide and what are the advantages (6( and disadvantages (2) of this material?

A

Replaces hydrogen atoms = improves surface wettability, deposit resistance and tear film stability

  • Very high Dks available
  • Few deposit problems
  • Better wettability
  • Suitable for EW
  • Fragile if too thin
  • Requires careful manufacture
  • Corneal adhesions in some cases
  • Dimensional stability depends on material and manufacturer
19
Q

What does a CLs aftercare H+S consist of? (9)

A
  • Type of lens worn
  • History of any previous lenses worn
  • Reason for visit
  • Any concerns (vision? comfort - end of day?)
  • Wearing time (Today; Days/week; Hrs/Day)
  • Care system - ask for demo
  • Ensure px has back-up spexs
  • Are the lenses meeting the needs of the px?
  • Pain/Irritation/Dryness?
20
Q

What needs to be recorded in a CLs aftercare examination?

A

1) Centration in primary gaze (mm)
2) Corneal coverage (complete or partial)
3) Upgaze blink
4) Horizontal lag
5) Push-up test

21
Q

Upgaze blink values for:

1) Optimal fit
2) Tight fit
3) Loose fit

A

1) 0.2 - 0.6mm
2) Little to no movement
3) > 0.6mm

22
Q

Horizontal lag values for:

1) Optimal fit
2) Tight fit
3) Loose fit

A

1) 0.2mm - 0.4mm
2) Little to no movement
3) > 0.4mm

23
Q

How is the push-up test recorded in CLs assessments?

A 
0% = Extremely loose
50% = Desired
30-70% = Acceptable
100% = Extremely tight
24
Q

Why is a tight fit bad (3)

A
  • Inflammation
  • Neovascularisation
  • Microbial Keratitis
25
Q

Why is a flat fit bad (3)

A
  • May cause limbal exposure
  • Vision may be unstable
  • Uncomfortable
26
Q

How do you optimise the fit for a:

1) Tight fitting lens
2) Loose fitting lens

A

1) Flatten BOZR (↑) or ↓ TD

2) Steepen BOZR (↓) OR ↑ TD

27
Q

Describe neovascularisation as a result of CLs wear and how to manage

A
  • Cornea gets most of its oxygen from the atmosphere
  • Putting lens in between therefore reduces the rate of oxygen passing through
  • Hypoxic damage leads to new blood vessels in oxygen deficient environments
  • Highly negative lenses are more thick at the edges
  • Move to a lens with higher Dk/t
28
Q

Describe microcysts as a result of CLs wear and how to manage

A
  • Cysts with distinct margins at the corneal epithelium
  • Made up of broken-down cellular debris
  • Seen with reversed illumination
  • Normally asymptomatic unless if seen in large amounts
  • Move to higher Dk/t if large amounts seen
  • Move to daily disposables if px on continuous wear lenses
29
Q

Describe vacuoles as a result of CLs wear and how to manage

A
  • Distinct margins and seen with non-reversed illumination
  • Occurs with hypoxia and oedema of the cornea
  • Move to higher Dk/t if large amounts seen
  • Move to daily disposables if px on continuous wear lenses
30
Q

What is polymegathism?

A

Changes in corneal endothelium whereby cells appear hexagonal and vary in size

31
Q

What is Meibomian gland atrophy?

A
  • Meibomian glands exist but do not function
  • Reduced secretion
  • Evaporative dry eye
  • Associated with ocular surface dryness
32
Q

1) What is Lid wiper epitheliopathy (LWE)?

2) How is LWE managed?

A

1)

  • Mechanical friction between lid wiper portion (between inferior and superior lid palpebral conjunctiva) and anterior surface of CLs
  • Due to insufficient lubrication between these surfaces
  • Staining will be seen with fluorescein

2)

  • Advise px to temporarily discontinue wear
  • Recommend artificial tears and encourage tissue healing with regular drops
  • Advise a lens with a lower coefficient of friction to ensure more comfort and to reduce friction
  • If px on RGP then move to hydrogel/SiHy
33
Q

Describe mucin balls and how to manage a px with mucin balls

A
  • Range from 20 to 200 microns in size
  • Surface mucins from tear film
  • Mechanical shearing affect between lens and the cornea
  • Caused usually by high modulus lenses (SiHy)
  • Found in pxs who have papillae
  • Much worse with overnight/extended wear lenses
  • Can cause indentations on the corneal surface (seen with NaFl)
  • Remove lenses and change lens type to lower modulus or daily lenses
34
Q

What are superior epithelial arcuate lesions (SEALs) and how are the managed in practice?

A
  • Shearing affect that disrupts the epithelial surface due to excessive upper lid pressure
  • Causes by high modulus lenses with a tight upper lid
  • Asymptomatic for px
  • Discontinue lens wear for a week and use artificial tears; refit with lower modulus lens and with smaller TD
35
Q

What is contact lens-induced papillary conjunctivitis (CLPC)?

A
  • Giant papillary conjunctivitis that is seen in patients wearing CLs
  • Immunological response to coated or deposited CLs where the mechanical irritation from deposits or high modulus CLs material cause a release of inflammatory mediators that contribute to CLPC
  • Papillae seen when lids everted
36
Q

What are the signs of contact lens-induced papillary conjunctivitis (CLPC)? (7)

A
  • Decreased lens tolerance
  • Increased lens awareness
  • Excessive lens movement
  • Increased mucus production
  • Redness
  • Itching
  • Burning
37
Q

What is the management plan for a patient with contact lens-induced papillary conjunctivitis (CLPC)?

A
  • Cease CLs wear for 2 - 4 weeks
  • Change to a more frequently changing lens
  • Mast-cell stabilisers or antihistamines in severe responses
  • Bring patient back in for regular follow-up
38
Q

What are the disadvantages of hydrogen peroxide solution?

A

Discomfort when residual peroxide is left due to solution not being neutralised properly (not enough soaking time)

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