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OD3 (S1&2) > CLM - Efficacy of Contact Lens Solutions - PAP Week 1 > Flashcards

CLM - Efficacy of Contact Lens Solutions - PAP Week 1 Flashcards

1
Q

What are the four main testing criteria for contact lens solutions?

A

Sterility
Preservative effectiveness
Microbial limits test
Stability

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2
Q

What does a standalone test for contact lens solutions evaluate?

A

Innate antimicrobial activity of the solution

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3
Q

What does a regimen test for contact lens solutions evaluate?

A

Efficacy of a contact lens disinfecting solution in a regimen

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4
Q

Describe the stand alone test in terms of what organisms are used to challenge the solution:
Gram + cocci
Gram - rod
Gram - mycobacteria
Yeast
Fungus

A

10^5 to 10^6 CFU/mL used
Gram + cocci
-staph. aureus
Gram - rod
-serratia marcescens
Gram - mycobacteria
-pseudomonas aureginosa
Yeast
-candida albicans
Fungus
-fusarium solani

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5
Q

What is the minimum recommended disinfectiongtime and describe how this relates to the primary criteria for a standalone test for bacteria.

A

Extent of viability loss determined at 25%, 50%, 75%, and 100% of the minimum recommended disinfection time
Bacteria - 3 log unit reduction (99.4%) within the MRDT

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6
Q

Describe the primary criteria for a standalone test for moulds and yeasts.

A

Reduced 1 log unit on average (90%) within the MRDT and no increase over a period x4 the MRDT

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7
Q

What test can be used if the primary criteria fails for a contact lens solution? What does it evaluate? What does it allow for?

A

Evaluates the antimicrobial efficacy of the entire regimen described in the cleaning instructions insert
Minimal level of anti-microbial activity acceptable for a contact lens solution, allowing for mechanical cleansing of the lens

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8
Q

What is required for a pass on the regimen test for bacteria, moulds, and yeast.

A

Bacteria - 5 log average reduction with a minimum of a 1 log reduction at MRDT
Moulds and yeasts - stasis over MRDT

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9
Q

List 6 shortcomings of the standalone test.

A

Limited number of bacteria tested
No acanthamoeba
No viruses
All microorganisms are lab strains, not clinical isolates
Testing methods dont account for organic matter (mucus/debris)
Sterile lab environment - not the real thing

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10
Q

What percentage of contact lenses get contaminated with daily wear, when does it occur, and what is the major source of conamination?

A

Up to 90% of lenses, occuring on day 1 of CL wear.
Lens handling is the major source of contamination.

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11
Q

When contaminated contact lens cases are cultured, describe what two main organisms grow (in percentages).

A

71% bacteria
9% acanthamoeba

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12
Q

What percentage of contact lens cases become contaminated?

A

80%

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13
Q

Do lens care accessories frequently get contaminated or rarely?

A

Common

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14
Q

What is the most common gram positive and negative (2) bacteria contaminating contact lens cases and solutions?

A

Positive - Staphylococci
Negative - Pseudomonas ssp. and enterobacteriaceae

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15
Q

What percentage of contamination occurrences do fungi/yeasts account for (case and solutions)? What about acanthamoeba?

A

Fungi - 20-40%
Acanthamoeba - 9%

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16
Q

What can chlorhexidine result in the prolonged survival of?

A

S. marcescens

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17
Q

Against what organism do PHMB and polyquaternium-1 have poor activity against?

A

Acanthamoeba cysts

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18
Q

Are 1-step 3% hydrogen peroxide systems effective against acanthamoeba? Describe why and explain for cysts and spores.

A

Acanthamoeba can survive 1-step systems because neutralisation is too rapid.
Cysts need a 1-2h soak
Spores need a 3-5h soak

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19
Q

What are the two major organisms in homemade and unpreserved saline?

A

Acanthamoeba (homemade)
Unpreserved (unpreserved)

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20
Q

What is the best product for straight kills when disinfecting?

A

Hydrogen peroxide

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21
Q

Describe the effect of the following on CFU. assume a 1m CFU start:
Rinsing
Rubbing and rinsing

A

Start - 1,000,000 CFU
99% decrease with rinsing - 3,000 CFU
99.9% decrease with rubbing and rinsing - 300 CFU

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22
Q

Is rubbing and rinsing adequately done?

A

No

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23
Q

What does acanthamoeba feed off when it contaminates contact lens cases/solutions?

A

Gram negative biofilms

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24
Q

Are acanthamoeba resistant to contact lens disinfectants?

A

Yes, especially cysts

25
Q

What will kill acanthamoeba cysts and trophozoites on contact lens cases (2)?

A

Scrubbing the case wells and very hot water (>70C for 1 min)

26
Q

How often should intermittent wearers disinfect their cases?

A

Weekly

27
Q

Consider extended vs daily wear. In which is the incidence of contact lens solution contamination higher? What about cases and contact lenses?

A

Higher incidence in daily wear
Similar for cases and contact lenses

28
Q

What is the main reason why rubbing is effective?

A

Biofilm formation

29
Q

Is there a difference in contamination rates between flat and cylindrical contact lens cases for RGPs?

A

No

30
Q

What is the likely state of contamination with asymptomatic wear of contact lenses?

A

CL less likely to be contaminated
Spectrum reflective of ocular biota

31
Q

What is the likely state of contamination of contact lenses if the cornea is imflammed?

A

CL colonisation by gram negative bacreria
Eyelid colonisation by S. aureus

32
Q

What three organisms are mostl likely responsible for a corneal infection with contact lens wear?

A

P. aureginosa
S. marcescens
Acanthamoeba spp.

33
Q

What is the evidence for non-compliance being a significant factor in contact lens contamination? What about microbial keratitis?

A

There is evidence both fro and against compliance being a significant factor
Non-compliance is a definite risk factor for microbial keratitis

34
Q

What are the three key non-compliance issues with contact lenses?

A

Handwashing
Rub and rinse step
CL case hygiene

35
Q

Can P. aureginosa strains be made resistant with repeated disinfectant exposure?

A

No

36
Q

List and describe the two types of P. aureginosa strains (2). Note which is more resistant to chemical disinfection.

A

Invasive
-enter corneal cells and replicate
-survive intracellularly without killing host
Cytotoxic
-remains extracellular
-kills cells
Cytotoxic is more resistant to chemical disinfection

37
Q

What strains of P. aureginosa are most susceptible to disinfection?

A

FDA/ISO strains

38
Q

If all contact lens solutions have similar efficacy for killing bacteria with similar shortcomings, what other factors should be considered (3)?

A

Cost
Convenience
Complexity

39
Q

What does contact lens solution hypersensitivity typically develop after?

A

Prolonged exposure

40
Q

Describe contact lens hypersensitivity. When does it resolve? How can it be treated (2)?

A

Recurrent, low level irritation/redness, limbal injection
Resolves upon CL removal
Resumes with CL resumption
Can use anti-histamines/inflammatories

41
Q

What should you always assess if you suspect contact lens hypersensitivity?

A

Palpebral conjunctiva

42
Q

Compare peroxide to polyquad on reported comfortable wearing times.

A

Peroxide resulted in longer comfortable wearing times on average

43
Q

Compare peroxide to multipurpose solutions on corneal infiltrate events and solution-induced corneal staining.

A

Peroxide had lower incidences of both corneal infiltrate events and solution-induced corneal staining.

44
Q

What is used to visualise solution-induced corneal staining?

A

NaFl or lissamine green

45
Q

What are three main factors that can affect corneal staining?

A

Dryness
Mechanical
Contact lens wear

46
Q

What is corneal staining generally regarded as?

A

Corneal compromise

47
Q

Define solution-induced corneal staining.

A

Diffuse punctate staining in at least four of the five regions (superior, inferior, nasal, temporal, central)

48
Q

What is solution-induced corneal staining thought to be induced by? Is it generally symptomatic or asymptomatic?

A

Thought to be induced by certain CL/solution combinations
Generally asymptomatic

49
Q

Is solution-induced corneal staining associated with other signs? Is it predictive of corneal infiltrate events or other adverse events?

A

No

50
Q

Does solution-induced corneal staining dissipate over time? Explain.

A

Yes, most obvious after 2h, and little left after 6h

51
Q

In what contact lens solution is incidence of solution-induced corneal staining lowest?

A

Peroxide

52
Q

What is the benefit of having higher concentrations of preservatives? What may it come at the expense of (2)?

A

Increased anti-microbial activity potentially at the expense of comfort and staining

53
Q

Are multipurpose solutions interchangeable?

A

No, patients should discuss any potential changes before using another product

54
Q

Describe the best practice for handling contact lenses (5).

A

-Handle CLs and accessories with clean, washed, and completely dried hands
-MPS 30 second rub each side and rinse with MPS prior to soak
-Fill case completely with CL solution
-Any time the CL is removed from the eye, it needs to be disinfected
-If lenses stored for >7 days, re-disinfection is required

55
Q

Describe the best practice for contact lens cases (5).

A

-Once lens is applied to the eye, discard the old solution
-Fill lens cases with fresh solution and scrub all internal surfaces including lids
-Discard solution
-Use lint-free cloth to wipe lens case dry
-Store in dry, clean, low humity area (NOT the bathroom)

56
Q

How often should lens cases be replaced according to the FDA? Is there any benefit in a faster replacement schedule?

A

Every 3 months
Some studies indicate a benefit in monthly replacement

57
Q

How often should CL solutions be replaced (peroxide, preserved, and MPS)?

A

MPS - every three months
Peroxide - 100 uses or 3 months, whichever first
Preserved saline - 14 days

58
Q

How often should lubricant eye drops be replaced?

A

1-6 months depending on preservative

59
Q

What 6 things should never be done with contact lenses?

A

-Using tap water to store, clean, or rinse contact lenses or cases
-Use expired cleaning solutions
-Top up CL case solution
-Reuse old CL case solution
-Refill smaller CL solutions from larger containers
-Use saliva as a rewetting agent (DESGUSTANG)

OD3 (S1&2) (114 decks)

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