Contact Lenses 1 Flashcards
why may patients drop out of the lens fitting?
-dryness
-discomfort
-redness
-convenience
-expense
-vision: this is the main reason as sometimes vision with CLs can be worse than with glasses
What are the advantages for assessing vision before lens fit (this is how it should be)
-for hard lens, tears correct astigmatism making it hard to get the Pxs original Rx before
-to allow time for lens to settle so you can get a more accurate assessment of the fit
-as you may dazzle the Px when assessing lens fit causing time wasting waiting for them to re-adjust from the bright light before assessing vision
what do you do if at any point of the lens fitting you find the fit is unacceptable?
start the process again right from choosing the initial trial lens but this time, choose a lens with a different manufacturer so you get a different sag instead of just looking at different base curve
What are the conditions for an optimal fitting lens
-good centration
-full coverage in all positions of gaze
-acceptable movement on blink and excursions
-comfortable
-clear and stable vision
when do you include OR in your CL Rx?
if it improves VA
if it makes sense with the spectacle Rx
when do you not include OR in your CL Rx?
-if it makes the VA worse
-you think you’ve given too much plus or minus when compared with the spec Rx
what can deposits on contact lenses cause?
-inflammatory complications including papillary conjunctivitis
-reduce lens surface wettability
-contaminate the CL case which is a high risk factor for CIE’s
-be a food source for microorganisms increasing the number of bacteria on the case or lens hence increasing risk of inflammation
what are the two main types of contact lens solutions?
MPS (multipurpose solutions) and peroxide solutions
how do MPS reduce hypersensitivity problems?
the preservatives have a large molecular weight so they don’t enter the lens matrix which would allow them to get into contact with the ocular surface
what percentage of contact lens patients use MPS?
96%
why may a patient choose peroxide instead of MPS to clean their CLs?
because peroxide is preservative free and so can be used by patients who are sensitive to MPS
what are the key functions and properties of contact lens solutions
*Effective disinfection against wide variety of
pathogenic organisms
* Non-toxic to ocular tissues
* Rapid disinfection capability
* Facilitate removal of lens deposits
* Condition lens surface to enhance
wettability & comfort
* Compatible with all CL materials
* Simple to use
* Affordable
what do preservatives in contact lens solutions do and how?
-they provide antimicrobial efficacy allowing them to work as a disinfectant
-by disrupting microbial cell membrane and inhibiting key enzymes
what are the two main preservatives in contact lens solution? What is the minimum recommended disinfection time when both these preservatives are used in one solution?
-polyhexanide
-polyquad
MRDT is typically4-6 hrs
what are the 4 key components of MPS solution?
-surfactant cleaner
-sequestering agent
-wetting agents
-tonicity and buffering agent
explain how surfactant cleaner is a key component in MPS
-by lowering the surface tension of a liquid
-acting as a detergent by forming micelles around the deposit
-acts as a wetting agent
explain how sequestering agents is a key component in MPS
They act on metal ions to improve disinfection efficacy and aid removal of tear film proteins like EDTA
explain how wetting agents are a key component in MPS
promote lens surface wetting improving comfort and relieve dryness and irritation
explain how a tonicity and buffering agent is a key component in MPS
it means the solution is maintained at a desired pH, tonicity and osmolarity which is important for comfort on insertion and integrity of the ocular surface
why is saline not good for cleaning contact lens cases compared to MPS?
saline has less ingredients and saline has 4x less preservative compared to a MPS as it is only to keep the saline itself from being contaminated. Not sufficient quantities to kill microbes hence why it’s only okay for rinsing CLs
what is saline only suitable for compared to what is MPS suitable for?
saline is only suitable for rinsing lenses only whereas MPS is suitable for daily conditioning, cleaning, removal of protein deposits, rinsing, chemical disinfection and lens storage
how does CL care solution tested?
- stand alone test
- the solution is incubated with a number of organisms
- stand alone test is passed when the solution has met primary criteria of 90% reduction in fungi and 99.9% reduction in bacteria
- if it does not meet primary criteria of standalone test then its tested against the secondary criteria
- secondary criteria is there has to be a combined reduction of 99.999% of bacteria, 90% reduction of each type of bacteria and fungal stasis at the minimum disinfection time
- when this is passes it can then pass on to the regimen test
- to pass the regimen test, there has to be a reduction of at least 99.99% for all organisms
what is a great MPS CL care brand?
Biotrue as it has good disinfecting efficacy and is great at reducing chance of development of both trophozoites and cysts of AK
name a great peroxide CL solution
Clear care
with peroxide CL solution, why is it important to allow the lenses at least 6 hours after adding neutralising agent before they are worn?
because above 100ppm of peroxide concentration, the patient can start to get stinging and redness which would make the CLs uncomfortable
Why is it especially important to clean contact lens cases?
as they can grow a biofilm which protects microbes from preservatives in CL solutions, providing a food source of acanthamoeba keratitis
Where does acanthamoeba come from?
protozoa commonly found in soil and fresh water, bacteria are the main food source
what are the two forms of acanthamoeba?
-trophozoites, activated feeding and dividing stage
-cysts, dormant and resistant
what is the two step system to using peroxide CL solution?
- surfactant containing
- neutralised to H2O and O2 by platinum disc or catalase tablet
- residual peroxide is toxic to ocular tissue
- there is then no ongoing disinfection so not suitable for long term storage
what is the hygiene, lens cleaning and case advice on insertion?
Wash & dry hands
* Apply lenses
* Empty case
* Rinse with solution
* Wipe with tissue
* Place case & caps face
down on clean tissue
what is the hygiene, lens cleaning and case advice on removal?
- Wash & dry hands
- Remove lens
- Rub & rinse lens
- Fill case with fresh
solution - Insert lens, re-cap case &
leave for at least MRDT
how do you help a patient choose a CL care solution?
- Availability in practice (often limited to one or two
manufacturers) - Specific indications / contra-indications of lens
- Px history / lifestyle
- Compliance
- Previous sensitivity problems
- Cost
If a toric lens has poor stability, what should you do?
-change manufacturer
-do a refit to make sure its not too loose or too tight
-change to a lens with a different method of stabilisation
What are the two types of soft toric lens stabilisation?
prism ballast
dynamic stabilisation
how does prism ballast stabilisation of toric lenses work?
-as the toric lens has an increasingly thicker profile towards the base
-the watermelon seed principle explains how the lens sits
-so the thinner portion of the lens is located under the upper eyelid and the thicker portion is squeezed towards the lower lid
what are the negatives of prism ballast lenses?
- reduced comfort
- thicker lens = reduced Dk/t
- prism in optic zone
- orientation affected by gravity
what is the positive of prism ballast lenses?
they are better for oblique cyls
what are peri ballast lenses?
toric lenses where as much prism as possible is removed from the lens through comfort chamfers and eccentric lenticulation to reduce lens thickness. Prism is restricted mainly to the lens edge allowing for a potentially free prism optic
how does dynamic stabilisation of CLs work?
- there are thin zones at the top and bottom of a lens which orientate beneath the lids
- the lids then squeeze against the thickness differential to maximise stability
what are the positives of dynamic stabilisation?
-better orientation for patients with tight or high lower lid due to minimal thickness differential
-gravity causes minimal rotation so more optimal for dynamic situations
what are the negatives of dynamic stabilisation?
limited to a correction of 4.00DC
what are the factors to do with the lids affecting stabilisation?
- Lower lid position
- Lid angles
- VPA
- Lid tension
- Force of blink
- Direction of movement
on blinking
what factors that are not associated with the eyelids affect lens stabilisation?
- Lens power
- Gravity
- Water content
- Material elasticity
- Lens thickness
what motivations may presbyopes have to wear contact lenses?
-wanting to wear contacts for their job
-may feel discomfort when they wear spectacle frames so can stop that is they have CLs
-may feel like glasses make them look older
-don’t want to be carrying around reading glasses with them
-so they can better do hobbie
give 2 reasons you may not fit specifically presbyopes with contact lenses
They may need very high detail of vision
If they need high visual demand
what kind of presbyopes may not be suitable for contact lenses?
-pxs with astigmatism
-patients that lack binocularity and stereopsis
-patients who don’t want to pay for the extra expenses compared to spectacles
-those with abnormally large pupils
how can you achieve higher success rates when fitting presbyopes with CLs?
-Fitting them earlier on in their presbyopia
-Aiming to fulfil most of their visual demands most of the time
-Careful H+S to establish requirements
-Manage expectations by discussing lens options, pros and cons and making sure they know they may have increased appointments to make sure the lenses are suitable
what are the three types of CL options for patients with presbyopia?
-over reader glasses on top of their normal CL prescription
-multifocals
-monovision
what are the two types of monovision contact lenses?
-enhanced monovision
-partial monovision
what are over readers?
SV near specs or varifocals used over the top of SV distance CLs
what are the positives of over readers as an option for presbyopes with contacts?
Easy to fit
Stable vision
High Rx/astigmatism
No compromise on VA, stereo or CS
Low cost
what are the negatives of over readers as an option for presbyopes with contacts?
-inconvenient
-low satisfaction
what are multifocal Cls?
where both eyes are corrected for multiple focal distances
what are the positives of using multifocals for presbyopes?
-suitable for BV problems
-possible for monocular pxs
-they are suitable for amblyopes or those with a strong dominant eye
-some designs provide intermediate correction
what are the negatives of using multifocals for presbyopes?
-higher cost
-vision may be less stable
-CL range is limited
-require more chair time
-need adaptation
what do multifocal torics do?
aim to correct both astigmatism and presbyopia
what are three negatives of multifocal torics?
-they have the additional requirement being stability
-the visual outcomes can be variable
-they are costly
who are partial monovision CLs good for?
-emerging presbyopes (<+1.00D add)
-to help adaptation in more advanced presbyopes
what is enhanced monovision?
where one eye is fitted with an SV CL and the other with a MF CL
what is a negative of enhanced monovision
it favours distance vision
what are the positives of enhanced monovision?
-may improve binocularity and visual experience
-lower cost than using MF in both eyes
what is partial monovision?
where a low Add like +0.75D is given to the non-dominant eye. this gives sufficient intermediate vision and then reading specs can be used for prolonged near work
what are the two types of multifocal contact lens designs? which is most common?
simultaneous and alternating. Simultaneous
what are the the three types of simultaneous multifocal designs
-concentric
-EDOF
-diffractive
how are multifocals not the same as varifocals?
multifocals may not necessarily have progression between the near and distance portion of the lens whereas varifocals do have progression.
what are the three types of concentric CL designs?
-bi-concentric
-aspheric
-multi-zone concentric
what kind of design do concentric multifocal lenses rely on?
centre surround design
what are the two types of bi concentric multifocal lenses? Which one is more popular?
-centre distance
-centre near (most popular especially in older patients as pupils constrict more with age meaning looking out of the peripheries becomes more difficult)
how do bi concentric centre distance lenses work in low illumination, high illumination, as sunspecs and what suffers as a result of pupil constriction with age?
Low illumination favours NV
High illumination favours DV
Sunspecs reading outside
Senile miosis – NV suffers
how do bi concentric centre near lenses work in low illumination, high illumination, as sunspecs and what suffers as a result of pupil constriction with age?
Low illumination favours DV
High illumination favours NV
Sunspecs for driving
Senile miosis – DV suffers
what are aspheric multifocal contact lenses?
offer a c/ontinuous change in power from centre to peripheral portion of optic zone and also have centre-distance to centre near designs which means they are still pupil dependnet
what does the effective near add depend on in aspheric multifocals?
the rate of change of aspherics
how are multizone concentrics different to other concentrics?
they minimise pupil dependence as zone width and spacing is based on the pupil size in different illuminations
how does light affect multi zone concentrics?
-DV is favoured in both high and low light conditions
-there is ab equal ratio of DV:NV in ambient illumination
what are the positives of concentric multifocal lens design
*Perform better than other simultaneous designs with high contrast targets
* Lenses can rotate freely without consequence
what are the negatives of concentric multifocal lens design
*Reduced CS/VA due to blurred image (suppressed)
* Perform poorer than other simultaneous designs with low contrast targets
* Decentration may lead to asymmetry and blur - coma aberrations
what are EDOF multifocals and how do they work?
extended depth of focus. It works by producing an extended area of focus where distance, near and intermediate vision are all clear with a very diffuse halo effect. EDOF is new so there is not yet much clinical study to see how good it really is.
what are the positives of EDOF multifocal lenses?
*Provides intermediate focus also
* Diffuse halo effect, minimal ghosting
* Pupil size independent
what are the negatives of EDOF multifocals?
- Image quality is reduced at the two true
focal points - Little evaluation of clinical performance
how do diffractive multifocals work?
diffractive multifocals rely on diffraction of light to produce the two focal points, one for distance and one for near
what are the positives of diffractive multifocals?
they are pupil size dependant
what are the negatives if diffractive multifocals?
- Reduced CS (contrast sensitivity)
- Centration dependent
- Not commercially available
what are alternating multifocal lenses?
when there is a distance focus on the top portion of the lens and the near focus on the bottom so the lenses physically move up on downgaze so when the patient looks down, the lens provide the patient with clear near vision. they are usually rgps
what are the requirements for the fit of alternating multifocals?
-Approx ¾ of pupil area must be covered by
correct segment of lens
-Require stabilisation and taut lower lid
-Lower lid should be no lower than inferior
limbus, to support the lens
-Should be minimal disturbance on blinking
what are the positives of alternating multifocals?
-independent of pupil size
-Add power customisable
-True single vision at distance
and near
-Good for high visual demands
what are the negatives of alternating multifocals?
-gaze dependant
-relies on lower lid tension
-fitting is typically more complex
-comfort is often reduced
what are the overall positives of simultaneous multifocal designs?
Fitting straightforward
Comfortable
Not gaze dependent
Suitable for enhanced monovision
Multiple Add sizes
Extended wear options
what are the overall negatives of simultaneous multifocal designs?
Small pupils less suitable
Small reduction in CS
Illumination dependent
Visual compromise difficult for some
Add size limited
what should you communicate to pxs who are presbyopes and are having Cls fit?
that their visual expectations will never be as good as glasses though so you should aim to meet around 80% of the px visual needs (WITHOUT TALKING ABOUT COMPROMISE)
nowadays do presbyopes use multifocal more or monovision more?
multifocals are more common
what are the two methods of assessing ocular dominance?
-sensory: this is the recommended for presbyope lens fit
-motor
give examples of presbyopic candidates who are good for monovision
-significant refractive error or astigmatism
-have reading positions other than standard downward gaze
-motivated and have realistic expectations
give examples of presbyopic candidates who are good for simultaneous multifocals
-are exisiting soft cl wearers who are emerging presbyopes
-have reading positions other than standard downward gaze
-moderate intermediate vision requirements
-have spherical or near spherical refractive errors
give examples of presbyopic candidates who are good for alternating multifocals
-early and advanced rgp wearing presbyopes
-lower lid position
-myopic or low hypermetropic powers
-normal to larger palperable apertures
-normal to tight lid tension
what are more challenging candidates for monovision?
-emmetropes, previously uncorrected hyperopes, low myopes
-concentrated specific visual needs
-high visual demands and expectations
what are more challenging candidates for simultaneous multifocals?
-those who wont accept compromise to distance vision
-emmetropic or near emmetropic distance Rx
-astigmatic
-small pupil size
what are more challenging candidates for alternating multifocals
-high hyperopes
-small palperable apertures
-loose lower lids
what considerations do you need to make when fitting patients who are presbyopes with contact lenses
*GH & Meds
* Dry eye & MGD
* Prescription & VA
* Astigmatism
* Binocular status, amblyopia
* Prism
* Difficulty with lens teach
how do you give prebyopes lens options and recommendations in the intial lens selection and fitting?
- Explain the different lens options in lay language
- Modality, material & presbyopic lens options
- Summarise pros and cons
- Explain why an option isn’t suitable
- Explain why an option may be more suitable
- Relate the options to their needs and expectations
- Give approximate costs
- Reassure patient that this is for the trial – they can
always try something else
how do you assess ocular dominance in presbyopes using sensory dominance method?
Alternate +1.00DS trial lens between best-corrected eyes. Ask the patient which gives the most subjective blur or change in binocular VA and the eye reporting more blur is the dominant eye
how do you optimise presbyopic lens selection
- Check spectacle prescription for new
fit and refit - Most plus/least minus Rx
- Determine lowest acceptable Add for
functional near vision - Determine BVD corrected mean
sphere for multifocal or monovision
spherical lenses - Determine BVD corrected sphere-cyl
for multifocal torics or monovision
toric lenses
how do you make sure you use CL fitting guides correctly?
make sure to only use them with their own specific brand of Cls and not with any others
what should you do after you have fit a presbyope with CLs?
- If visual performance is acceptable then offer lenses for
trial - Reassure patient that neural adaptation can take some
time, visual performance likely to improve - Advice about adaptation – driving, etc
- Advice about limitations – night driving, low illumination
levels - Book in for aftercare (follow-up) in 1-2 weeks
- Contact the practice if any concerns
