CLM - Soft Contact Lens Maintenance - Week 8 Flashcards
List 6 key requirements for contact lens solutions.
Antimicrobial efficacy
Non-toic to ocular tissue
Minimum effect on lens parameters
Simple to use
Convenient
Inexpensive
List 7 possible components of a contact lens solution.
Water
Osmolarity adjusting agents
Buffering agents
Surfactants
Preservatives/disinfectants
Chelating agents
Viscosity enhancing agents
Give an example of an osmolarity adjusting agent and an ideal percentage. What else can it be used for?
Sodium chloride, adjusts tonicty to the same level as tears, ideally 0.9-1.1%
Can be used in much larger amounts to enhance cleaning/antimicrobial action (hypertonic)
What is a buffer solution and what doth it do?
A combination of weak acids or bases and their salts
This stabilises and maintains preferred solution pH under varying conditions
What determines the buffer and final pH to be used in a contact lens solution?
The preservative type
List the 5 components of lens care routine.
Handwashing
Surface cleaning
Rinsing
Disinfection
Enzymatic cleaning
Case care
When handwashing, what should be avoided?
Soaps with added moisturisers/perfumes/scents etc
What is the most important step in lens care routine?
Surface cleaning
What log unit reduction in microorganisms occurs with surface cleaning?
2-4 log unit reduction, up to 99.9% removal
Whats more important, the cleaning process of a lens or the brand of cleaner used?
Cleaning process
When must surface cleaning be done?
Every time the lenses are taken off.
What is surface cleaning typically conducted with?
Multipurpose solutions, but daily cleaners are available
What is the purpose of rinsing after surface cleaning?
Flush loosened debris and remove cleaner
What occurs with disinfection? Is sterilisation achieved?
Reduction of microbial contamination to safe levels, inactivating all pathogenic microorganisms, but not all microbial forms
Sterilisation is not the aim, and is not achieved
What is the mosr common form of contact lens disinfection? How is microbial death achieved (2)?
Chemical disinfection
Dissolves cell membrane lipids
Denatures proteins essential for function
List 4 physical methods for soft contact lens disinfection. Is this common?
Thermal
Microwave
Ultraviolet
Ultrasound
Rare now
List 5 types of chemical methods for soft contact lens disinfection.
Biguanides
Quaternary ammonium compounds
Hydrogen peroxide
Sorbic acid
Thimerosal (autistic screeching)
What is an advantage of disinfection using microwaves?
Effective and rapid elimination of bacteria via inhibition of metabolism
What are 4 disadvantages of disinfection using microwaves?
Long term effect on lens polymers could be damaging
Difference in microwave brands/outputs etc
Initial cost of the microwave
Lack of portability
Describe hydrogen peroxide as a disinfectant.
Strong oxidising agent at 3%
Toxic to the eye and requires inactivation using a tablet or liquid or platinum
What is the minimum soaking time in hydrogen peroxide before neutralising? What is recommended?
Minimum 3 hours
6 hours recommended (overnight)
List 4 advantages of hydrogen peroxide for contact lens disinfection.
Preservative free
Broad antimicrobial efficacy
Creat for conventional soft lenses
Less staining than chemical solutions for SiH lenses
List 4 disadvantages of hydrogen peroxide for contact lens disinfection.
Residual peroxide may cause discomfort and hyperaemia
Little to no ongoing disinfection capability
Expensive
More difficult/lower compliance (not with the one step system)
List two old generation disinfectants and why they are classed so. What to new generation disinfectants have that prevents this?
Chlorhexidine and thimerosal
Due to uptake into the lens matrix
Newer generation disinfectants have larger molecules, minimising absorption
Are bacteria and/or viruses superficial on the lens? Can they fit into the pores of the lens and infiltrate the matrix?
No, they are superficial on the lens and cant fit into the pores
What are biguanides?
Cationic antiseptics
Do biguanides have a large or small molecular size? How long does it take to achieve disinfection?
Large, disinfection takes 4-6 hours
What is a disadvantage of biguanides?
Small percentage of patients show sensitivity, some issues with SiH lenses
What are quaternary ammonium compounds and what are they effective against? How long do they take to disinfect?
Cationic detergents, effective against bacteria and fungi
Takes 6 hours to disinfect
List 4 advantages of multipurpose solutions.
Convenience
Reduced cost
Eliminate saline
Enhance compliance
List two disadvantages of multipurpose solutions.
Possible compromised efficacy
Solution toxicity/sensitivity
Compare multipurpose solutions to hydrogen peroxide in terms of corneal staining caused.
Multipurpose solutions cause significantly more asymptomatic corneal staining than hydrogen peroxide for SiH lenses
What is still required with no rub solutions? Is it better than rubbing?
Still requires significant rinsing procedure, as long as 20 seconds
Rubbing is always better
What is better for SiH, multipurose solutions or hydrogen peroxide?
Hydrogen peroxide
What is recommended for lenses not replaced daily in terms of cleaning (2)?
Separate daily cleaner and enzyme cleaning
What do enzymatic cleaners do?
Removes bound insoluble protein
What increases with the age of a contact lens?
Immunogenic potential of bound proteins
What should always be done before and after enzymatic cleaning?
Surface clean and rinse
How are cases cleaned (3)?
Hot tap water
Disinfecting solution/saline and toothbrush/cotton-bud
Air drying
How often should lens cases be replaced?
Every 3 months
How do antibacterial lens cases work? What is needed for it to maintain activity?
Contains silver which is broad spectrum
Requires moisture to maintain activity
List 7 uses for rewetting drops.
Alleviating dryness/discomfort
Flushing irritating particles from the eye/lens
Rehydrating lenses
Marginal dry eye patients
Dry/windy conditions
Tired eyes
Mild allergy symptoms
