Overnight wear of contact lenses Flashcards
how many patients are found to take naps in their CLs
50%
how many night does:
Continuous wear
Extended wear
Flexible wear
refer up to
Continuous wear refers to up to 30 nights
Extended wear refers to up to 6 nights (a 2 weekly lens goes down to 1 week i.e. the modality/frequency decreases)
Flexible wear: occasional overnight wear
what is the risk of overnight CL wear
the eye is deprived of oxygen and the lens will sit tightly and become dehydrated = complications associated with CL wear
give 4 reasons why people will choose to wear lenses overnight
Convenience
- No cleaning every day
- Less use of solutions reduces cost
- No removing the lens everyday
- Clear vision when waking (for high myopes)
Lifestyle
- Certain occupations
Therapeutic bandage CL
High Rx and aphakes
why is Therapeutic bandage CL used and how is it changed
- eye protection from the wind
- elderly patients
- sensitive corneas
hospital changes the lens every month, px does not change if carer is not there
give 4 reasons why you do not want to fit EW lenses
- Relative to daily wear (DW) there is a significant increase
in the risk of a serious adverse event
e.g. microbial keratitis is more likely to occur due to the build up of deposits on the lens as its not coming out and being cleaned - Hypoxic environment- closed eye, less tear circulation
- Frequent monitoring is required
px has to visit more, every 3 months - Needs to be an ‘ideal’ px
The environment needs to be ideal - hygienic surroundings
The px needs to be very compliant - need to come back for aftercare
The px needs to be vigilant - make px aware there could be infection and signs of them
what 3 qualities should an EW lens have to compensate for the hypoxic environment it creates for the cornea
- make sure fitting is not tight and that they move well
- lens should have good wettability
- make sure of no deposit build up
what was one of the earliest overnight lenses made from, when were they created and up to how long could they be used
- glass haptic lenses
- fitted in the 1880s
- worn continuously for up to 2 years at a time
what lens was created in 1970,
what type of material was this and what was more feasible with this.
when did the use of these lenses increase
- the Permalens (developed by John de Carle from London)
- gas-permeable material
- rigid lenses for EW more feasible
- their use increased gradually in the 1980s
what did the FDA improve in 1981
extended wear hydrogels for cosmetic correction
how many americans were wearing EW lenses by 1985
what concerns were there about EW lenses by the end of the 1980s and what happened as a result
4 million Americans wearing EW lenses
By the end of the 1980s there
were concerns about incidence of microbial keratitis in EW patients. Majority of papers suggested that soft EW was the major concern, but the publicity affected the EW market for all lens types.
what did the poggio and schein study impact
Reported incidence of keratitis was
- 4.1/100,000 in daily CL wearers,
- 20.9/100,000 in Extended Wear patients.
- Other studies supported similar findings
- Confidence lost in EW lenses
as this figure was enough to change the value in the FDA guidance
what did the FDA do in 1989
recommended that EW Hydrogel CL wear should be limited to 6 nights and 7 days. After this px must remove lenses
what did the FDA do in 1999
approved use of SiH lenses for up to 30 days CW
oxygen is not an issue for SiHy lenses, but hoped that microbial keratitis risk was not so bad
which are the most common groups of people to be prescribed CW lenses
older patients and males
list 5 changes that occur in closed eye conditions
- Available oxygen reduces (from 155mmHg to 55mmHg)
- Demand for corneal oxygen increases
- pH changes from 7.45 to 7.25
- Tear osmolarity decreases
- Increased oedema
what is the Holden and Mertz criterion and which lenses did not meet this criteria
minimum Dkt required to prevent central oedema during overnight wear
it is the formula that tells you how much o2 is required by the eyes to prevent central corneal oedema
it has 2 versions: a DW and a EW equation
most hydrogels didn’t meet the criteria
what does oxygen availability to the cornea depend on with the lens
depends on oxygen
permeability (Dk) and the thickness of the lens (t)
what is the Dk of conventional lenses related directly to
the amount of water the polymer can hold-oxygen
dissolves into the water aspect of the material and
diffuses through the lens
what does Dk increase logarithmically with
with increasing water content of the material
what was necessary to increase the Dk of conventional hydrogel materials
to incorporate monomers that would bind more water into the polymer (SiHydrogels)
what is the advantage of high water content lenses and what is the drawback
- it provides more o2 to the eye
- but dehydrates quicker (lens is more uncomfortable and vision becomes unclear) and it is more harder to handle as its too fragile
what 2 other lens materials will be better suited for EW use over hydrogels
- RGP
- SiHydrogels
give 4 reasons why RGPs will be good for EW wear
- Greater oxygen permeability than some conventional soft lenses (hydrogels) because they contain fluorine or silicone - both these
materials have good ability to
transport oxygen - Smaller lenses compared to soft, which also aids oxygen provision
- Better tear exchange and lens mobility which flushes away toxins and debris that could lead to an inflammatory event. Active tear pump
- Less lens dehydration
Oxygen is not an issue for SiHydrogel lenses to be used for EW, but give 2 reasons and explain why for each that they are not perfect
- Mechanical issues:
SiH materials are stiffer than hydrogels due to the incorporation of silicone.
This was esp a problem with first generation SiH e.g. by causing mucin balls from the post lens tear film - Surface properties: decreased wettability and increased lipid deposition. Although more modern SiH are coated with a more hydrophillic coating
give an example of what the mechanical issues of SiH lenses had which wasn’t great for EW
causing mucin balls from the post lens tear film, due to the stiffer material
give 2 advantages and 1 disadvantage of High/Hyper Dk rigid lenses for overnight wear
Advantages:
- Better tear interaction
- Hypoxia less of an issue
Disadvantage:
- Lens binding, staining problems
give the 2 disadvantages of Hydrogel lenses for overnight wear
- Hypoxia related problems
- Protein, and other deposit, build up
give 2 advantages and 1 disadvantage of SiHydrogel lenses for overnight wear
Advantages:
- Protein less of an issue
- Hypoxia less of an issue than hydrogels
Disadvantage:
- Lipid build up
what is the fitting criteria for overnight lens wear and why
- similar to daily wear, but
lenses need to move more to allow tear exchange – flushes away debris. - because we want to minimise hypoxic effects- a tight lens won’t help
what 2 things is important to discuss with your px when fitting them with overnight wear CLs
what must you ensure your px can do before allowing them to take their overnight CLs
- Discuss the increased risk of microbial keratitis with your patient - use the CoO guidelines and you must write down that you discussed this
- Discuss the need for proper aftercare appointments - only fit someone if they’re able to come back for their aftercares
- Your patient must be able to remove lenses themselves. If the patient has extended wear lenses because of their disability and is unable to handle them, you should teach their carer how to remove the
lenses
what 5 things do you need to find out when assessing patient suitability for overnight CL wear
- Consider px lifestyle
A good history and symptoms will reveal if px sleeps in CL - Are they a smoker?
- Their motivation:
profession/vocation, therapeutic reasons - Their previous CL history and ocular health
Blepharitis, hayfever, history of eye infections, history of infiltrates, poor compliance, MGD, dry eyes - Consider the px general health
If poorly or diabetic don’t fit
why do you not want to fit a diabetic patient with overnight CLs
because they have an increased risk of inflammation
so daily wear is better
what type should patients new to CLs adapt to first
when should all overnight CL wearers initially be seen first
what order/pattern do some suggest the follow up visits of overnight CLs occur as
- Patients new to contact lenses should adapt to daily wear first
- All wearers should be seen for an initial follow-up visit after the first overnight wear (first morning after wearing CLs)
- after 1 night (morning
appt) , 7 days, 1 month, 3 months
what 4 things may the follow up visits frequency of overnight CLs depend on
and what should CW/EW lenses frequency of follow up visits always be more frequent than and why
- Clinical status
- History
- Type of lens
- Modality of wear
follow up should be greater for CW/EW wearers than DW wearers, due to increased risk of complications
what 3 questions should your patient be able to answer ‘yes’ to when wearing EW/CW lenses
and what should they do if the answer to this is no
Do the eyes look good?
Do they feel good?
Can I see well?
If the answer to any of these questions is no, px should remove their lenses and seek help asap
what 2 things should your patients who are wearing EW/CW lenses be aware of and what an you do to help them
Your patient should be aware of the signs and symptoms of complications
The px also be made aware of emergency contact procedures.
You should give your patient an out-of hours phone number and local eye casualty details at the time of the CL teach.
by written and verbal advice
during your follow up visit of a EW/CW lens wearer patient, what 3 things will you examine
- Examine lens quality
- Examine lens movement
- Examine the eye
what 2 things will you be looking out for in your a/c exam of your EW/CW wearer when examining their lens quality
- are there deposits?
- problems with wettability of
lens?
why will you examine lens movement in your a/c exam of your EW/CW wearer
because it is important for overnight CL wear, but not excessive movement
give 3 reasons as to why you want to examine the eye itself in your a/c exam of your EW/CW wearer
to look for signs of infection, hypoxia, mechanical effects of CL
list 6 possible problems that can occur in a px who is wearing EW/CW lenses
- Inflammatory reactions
Infiltrates, contact lens acute red eye - Mechanical complications
e. g. SEALs, Contact lens associated papillary conjunctivitis, mucin balls, lens binding - Infections
e. g. Microbial keratitis - Other signs of hypoxia
e. g. Endothelial polymegethism, microcysts and vacuoles, oedema - Lens deposit build up
- Staining
e. g. 3 and 9 o clock
give 2 examples of inflammatory reactions than can occur in the eye from EW/CW lens wear
- Infiltrates
- Contact lens acute red eye
give 4 examples of mechanical complications than can occur in the eye from EW/CW lens wear
- SEALs
- Contact lens associated papillary conjunctivitis
- mucin balls
- lens binding
give an example of an infection than can occur in the eye from EW/CW lens wear
Microbial keratitis
give 4 other signs of hypoxia than can occur in the eye from EW/CW lens wear
- Endothelial polymegathism
- Microcysts
- Vacuoles
- Oedema
give an example of a corneal staining than can occur in the eye from EW/CW lens wear
3 and 9 o’clock staining
