CLM - Efficacy of Contact Lens Solutions - PAP Week 1 Flashcards
What are the four main testing criteria for contact lens solutions?
Sterility
Preservative effectiveness
Microbial limits test
Stability
What does a standalone test for contact lens solutions evaluate?
Innate antimicrobial activity of the solution
What does a regimen test for contact lens solutions evaluate?
Efficacy of a contact lens disinfecting solution in a regimen
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
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
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
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
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
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
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.
When contaminated contact lens cases are cultured, describe what two main organisms grow (in percentages).
71% bacteria
9% acanthamoeba
What percentage of contact lens cases become contaminated?
80%
Do lens care accessories frequently get contaminated or rarely?
Common
What is the most common gram positive and negative (2) bacteria contaminating contact lens cases and solutions?
Positive - Staphylococci
Negative - Pseudomonas ssp. and enterobacteriaceae
What percentage of contamination occurrences do fungi/yeasts account for (case and solutions)? What about acanthamoeba?
Fungi - 20-40%
Acanthamoeba - 9%
What can chlorhexidine result in the prolonged survival of?
S. marcescens
Against what organism do PHMB and polyquaternium-1 have poor activity against?
Acanthamoeba cysts
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
What are the two major organisms in homemade and unpreserved saline?
Acanthamoeba (homemade)
Unpreserved (unpreserved)
What is the best product for straight kills when disinfecting?
Hydrogen peroxide
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
Is rubbing and rinsing adequately done?
No
What does acanthamoeba feed off when it contaminates contact lens cases/solutions?
Gram negative biofilms
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?
No
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?
No
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?
No
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)
