CLM - Efficacy of Contact Lens Solutions - PAP Week 1 Flashcards by Davud Akgun

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

Sterility
Preservative effectiveness
Microbial limits test
Stability

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What does a standalone test for contact lens solutions evaluate?

Innate antimicrobial activity of the solution

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What does a regimen test for contact lens solutions evaluate?

Efficacy of a contact lens disinfecting solution in a regimen

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

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

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

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

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

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

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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List 6 shortcomings of the standalone test.

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

Up to 90% of lenses, occuring on day 1 of CL wear.

Lens handling is the major source of contamination.

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

71% bacteria

9% acanthamoeba

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What percentage of contact lens cases become contaminated?

80%

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Do lens care accessories frequently get contaminated or rarely?

Common

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

Positive - Staphylococci

Negative - Pseudomonas ssp. and enterobacteriaceae

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

Fungi - 20-40%

Acanthamoeba - 9%

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What can chlorhexidine result in the prolonged survival of?

S. marcescens

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

Acanthamoeba cysts

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

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

Acanthamoeba (homemade)

Unpreserved (unpreserved)

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What is the best product for straight kills when disinfecting?

Hydrogen peroxide

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

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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Is rubbing and rinsing adequately done?

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

Gram negative biofilms

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Are acanthamoeba resistant to contact lens disinfectants?

Yes, especially cysts

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

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

How often should intermittent wearers disinfect their cases?

Weekly

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

Higher incidence in daily wear | Similar for cases and contact lenses

What is the main reason why rubbing is effective?

Biofilm formation

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

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

CL less likely to be contaminated | Spectrum reflective of ocular biota

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

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

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

P. aureginosa S. marcescens Acanthamoeba spp.

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

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

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

Handwashing Rub and rinse step CL case hygiene

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

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

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

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

FDA/ISO strains

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

Cost Convenience Complexity

What does contact lens solution hypersensitivity typically develop after?

Prolonged exposure

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

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

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

Palpebral conjunctiva

Compare peroxide to polyquad on reported comfortable wearing times.

Peroxide resulted in longer comfortable wearing times on average

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

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

What is used to visualise solution-induced corneal staining?

NaFl or lissamine green

What are three main factors that can affect corneal staining?

Dryness Mechanical Contact lens wear

What is corneal staining generally regarded as?

Corneal compromise

Define solution-induced corneal staining.

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

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

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

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

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

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

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

Peroxide

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

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

Are multipurpose solutions interchangeable?

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

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

- 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

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

- 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)

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

Every 3 months | Some studies indicate a benefit in monthly replacement

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

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

How often should lubricant eye drops be replaced?

1-6 months depending on preservative

What 6 things should never be done with contact lenses?

- 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)