Care regimes 1 Flashcards
name 2 reasons why contact lens solutions are needed
- to provide water: some sort of liquid to avoid SCL drying out (not needed for RGP)
- cleaning and disinfecting: for both SCL and RGP
what changes all the time with solutions and is important to understand
market is always changing
why is a solution prescribed to a contact lens patient
to provide CL maintenance to the needs to individual patients
hence px should not buy any old solution and should continue with the same product as prescribed
list the 6 contact lens requirements i.e. a contact lens solution must be…
- antimicrobial: to kill bugs once the bottle is open or in the case
- fungicidal capacity: not much in this country, more relevant for hotter countries
- non-toxic to the eye: as eyes are sensitive and the sol will be going into the eye
- minimal effect of lens parameters: should not change the shape of the CL, however long it is sitting in the sol
- chemically stable and transparent: as its going into the eyes (only acceptation is cleaner as that is not going into the eyes)
- inexpensive, convenient and simple to use: or patient can become in compliant
list the 7 components in a CL solution formulation and state the purpose of all these ingrediants
- buffers
- viscosity agents
- wetting agents
- lubricating agents
- preservatives
- surfactants
- tonicity agents
to do with comfort and tear smoothness in the eye
what 3 possible things can buffers be composed of
- sodium phosphate
- borate
- boric acid
what is the ph of the tears and what range do buffers maintain ph within
hydrogen ion concentration pH of tears is 7.0 - 7.4 (a broader range than buffers)
buffer maintains pH within narrow limits of 6.6 to 7.8
when can buffers cause discomfort
if the tears pH is outside the buffering salts capabilities
e.g. a red eye or lacrimation means the tears are outside of the range of that pH solution
what is the purpose of having buffers in a CL sol formulation
acts to enhance anti-microbial activity which contains: EDTA (ethylene diamine tetra-acetic acid)
and for maintenance of the pH of the tears
what affect does a viscosity agent have in the CL solution
increases the thickness of the sol - to make it feel more slick
why do viscosity agents increase the thickness of the CL solution and name an ingredient used as
it improves contact time of the lens on the eye
methylcellulose: usually for RGP lenses as it can be uncomfortable when putting lenses in, the solution will then stay around for a little while whilst the eye is adapting to the lens being in the eye - this helps with initial comfort when lens goes into eye
which types of contact lenses need wetting agents in the sol formulation
soft and RGP lenses
what is the reason for a wetting agent in a CL sol
encourages wetting on insertion by aiding the spread of the solution across the lens surface, used for prolonged all day comfort of CL
what is the name of the wetting agent used in RGP sol
polyvinyl alcohol, polysorbate 80
used if RGP lenses are stored wet, which produced initial comfort, especially for children
what is the name of 4 different possible wetting agents used in SCL sol
- pro-vit 85
- propylene glycol
- poloxamer 407
- polyquaternium 10
in which circumstances is the use of a wetting agent contradicted
all day staring e.g. pc screens does not work with the wetting agent and instead lose it quickly
list 4 reasons why a lubricating agent is used in a CL sol
- reduce surface tension: spreads tears over surface and improves gettability
- improves wettability:
- increase viscosity: slick feel of sol
- in second generation SCL solutions: otherwise water is lost by staring, blinking and hot weather, so still need viscosity of sol to prolong comfort and wettability
name the 4 different possible lubricating agents found in second generation SCL sol formulation
- HPMC (hydroxypropyl methyl cellulose)
- polyquarternium 10
- lubricase
- hyaluronan (HA) - B&L BioTrue - which matches the pH of healthy tears and keeps certain beneficial tear proteins active, good for both silicone hydrogel and hydrogel lenses
what is the purpose of having a preservative in a CL sol formulation
for disinfection
name the 7 main preservatives found in CL sol
- benzalkonium chloride (BAK)
- chlorhexidine
- thiomersal
- polyquats - polyhexanide and polyquad
- aldox
- sodium chlorite
- alexadine
name the two agents found in surfactants of a CL sol
- chelating agents
- sequestering agents
list all the properties of chelating agents, found in surfactants of a CL sol
- removes calcium and magnesium: EDTA (sodium edetate)
- cleans lens of proteinaceous material: and gives better wettability
- solubalise lipoidal debris
- claims:
- adherence to surface for better wettability
- more comfortable
list all the properties of sequestering agents, found in surfactants of a CL sol
- negatively charged
- used in combination with surfactants to enhance activity
e. g. citrate, hydranate, tri-klens - to get rid of everything thats loaded on the lens from tears and atmosphere etc
what is the purpose of having tonicity agents in a CL sol formulation
to ensure compatibility with the tears
name two possible tonicity agents found in the formulation of CL sol
- sodium
- potassium chloride
what can changes in tonicity result in
discomfort and hyperaemia on insertion and a lot of lacrimation
list the 4 different types and properties of tonicity agents
- Tears ~0.9% NaCl solution (salt in tears)
- hypertonic - reduces corneal thickness
- hypotonic - increases corneal thickness
- 1.5 % gives discomfort
matches most px, but not all
what is regarded as ‘disinfection’
- the reduction of microbial contamination to ‘safe’ levels
- the eye is not a sterile environment, so disinfection rather than sterilisation (px needs to understand that not eliminating them, but keeping the bugs down to a safe level)
what is the uncompromised cornea good at
effective as eliminating organisms as bugs can’t get through the surface
if the cornea was compromised, bugs can get through which are attached to the CL
list all the reasons for case hygiene
- regular replacement is essential due to the build up of micro-organisms which secrete a protective layer called glycocalyx/biofilm where this biofilm can become a reservoir of contamination which bugs can live off
- up to 45% of CL cases are contaminated with an array of pathogens - due to the biofilm of glycocalyx
- most frequent bacteria are: staphylococcus, basillus ssp and fungi
- different types of bugs hang out at different places
list the three different types of test organisms for CL sol and the names of their microbes
- bacteria
- pseudomonas aeruginosa: major MK bug
- staphylococcus aureus
- serratia marcescens - fungi
- candida albicans
- fusarium solani - acanthamoeba
- not required and no standard test methods, so px needs to understand care of lenses
list and explain the three measures of disinfection efficacy
- D-value: the time to reduce organism population by 90% (1 log unit) - not sterile but safe
- safety factor: number of D-values by which infection time is specified by the manufacturer (MRDT) exceeds time to achieve 0 viable units of most resilient organisms
- solution power: MRDT/D-value: solution power has to be quoted since solutions have reduced power but are 2-step program option so there is another solution to get to a safe level of disinfection
name the standard requirement code for methods of evaluating disinfectant efficacy
ISO 14729 - requires a two stage test of contact lens disinfectants
name the two stages of testing of contact lens disinfectants
- stand alone test
- regimen test
state how the stand alone test is carried out for testing of contact lens disinfectants
- 10ml of disinfectant is challenged with 1 million organisms/ml of three standard bacteria and two standard fungi
- viable organisms remaining at the end of the recommended soaking time are counted
state how the regimen test is carried out for testing of contact lens disinfectants
- 20 CLs are contaminated with 100,000 organisms of each of the test bacteria and fungi
- lenses are put through the full recommended care regimen and remaining viable organisms are counted
what do the two stages of testing of contact lens disinfectants (stand alone test and regiment test) make sure of
that the organisms that are left over are viable and safe numbers
what is the two requirements of the stand alone test for contact lens disinfectants
- primary standard
- product reduces bacterial challenge by 99.9% and fungal challenge by 90% for each organism type - secondary standard
- can be part of a disinfection system if the regimen test is passed - products reduces bacterial challenge by at least 90% for each organism and fungi do not grow
what is the requirement of the regimen test for contact lens disinfectants
no more than 10 viable organisms per lens should remain - once it has been through the full system
- px needs to know that this is not sterile, but that lenses have been disinfected to a safe level
list the 6 things that efficacy of disinfection is dependent on
- concentration
- pH
- exposure time: how long the lenses need to be in the sol for, always read the label
- temperature and humidity: cold temperature can slow down disinfectants e.g. with hydrogen peroxide
- organic material present
- type/condition of material to be disinfected
list the properties of quaternary ammonium compounds for disinfection
e.g. benzalkonium chloride (BAK) 0.001-0.10% (found in eye drops)
- little used for SCL as it binds to methlyacrylic acid
- peak antibacterial effect at alkaline pH
- not compatible with NaFl (flourescein)
list the properties of biguanides for disinfection
e.g. chlorhexadine digluconate (CHX) - not used anymore
- surface active cationic disinfectants
- absorbed into -ve bacterial surface, to make sure bacteria is reduced by:
- disruption of cytoplasmic membrane
- precipitation of the contents
- binds readily to the mucus
- causes sensitivity reactions - 15% patients had a reaction to it, found diffuse punctate staining over the whole cornea due to toxicity of solution
list the properties of organic mercury compounds for disinfection
e.g. thimerosal (THI) - sodium ethyl mercurithiosaliclate
- poor antibacterial but better anti fungal agents
- release of mercurial ions
- not compatible with BAK
- allergic response - more acute and at superior cornea, doesn’t work well with SCL
list the properties of aldox for disinfection
- included in formulations with polyquad
- better activity against fungi
- interacts with cell wall components
- allows penetration of the protective coating or fungal cells
- better activity against acanthemoeba cysts: but can’t really compare acanthamoeba between different products because it occurs in different stages and manufacturers may test at different stages of the acanthamoeba
list the properties of sodium chlorite for disinfection
- mainly uses for silicone hydrogels
- generates chlorine dioxide
- effective against gram -ve and gram +ve bacteria
- effective against yeast and fungi
- activated with peroxide
- found in municipal drinking water
list the properties of alexidine for disinfection
- more compatible with silicone hydrogel
- bis-biguinide (mouthwash)
- same reaction on cell walls as polyquats
- effective against acanthamoeba (in a particular form)
list the properties of lysozyme for disinfection
- natural disinfectant present in the tears in high concentration
- potent anti bacterial enzyme
- particularly effective against gram positive (less worse) bacteria - if not denatured
list the properties of alcohols for disinfection
e.g. 20% isopropyl alcohol
- highly efficient antimicrobial performance
- effective against resistant organisms
- highly effective in dissolving lipids: good with yearly silicone hydrogels
- not compatible with certain RGP materials
list the properties of hydrogen peroxide for disinfection
- most effective: will kill all states of acanthamoeba if lenses are left in the solution over night
- broad spectrum antibacterial
- pH adjusted to prevent breakdown
- must neutralise the solution
- catalyst: peroxide -> water and oxygen
2H202 -> 2H20 + 02
list the properties of polyquats for disinfection
- acts by disrupting cell walls
- they’re selective
- positively charged polyquats bind to negatively charged phospholipids found in bacterial cell membrane (want the charge to be opposite for destruction to happen)
- destroys the integrity of the cell, allowing cell constituents to leak out the membrane causing cell death
what is the definition of cleaning
the removal of accumulated deposits and micro-organisms from the lens surface, can be mechanical (rubbing or rinsing) or passive (soaking/rub free)
what is the definition of disinfection
the reduction of micro organisms to safe levels (not complete eradication). rubbing and rinsing can contribute significantly to disinfection
what is the definition of rinsing
it is essential for good cleaning as it removes loosened deposits and dead micro-organisms from the lens
list the 5 types of contact lens care products for SCLs
- cleaner: mostly for > 3 monthlies
- rinsing solution: saline
- disinfectant
- protein removal
- rewetting
list the 5 types of contact lens care products for RGPs
- cleaner
- saline: to wash off the cleaner
- conditioning and disinfection
- protein removal
- rewetting
