contact lenses Flashcards
give the 2 different types of hard contact lenses
-AKA rigid corneal lenses
-rigid gas permeable (RGP)
give 2 types of soft CLs
AKA hydrogels, HEMA lenses
what are the three sizes of hard contact lenses?
-corneal
-semi scleral
-scleral
give an example of a therapeutic CL
a bandage lens
what are the soft lens modalities?
-daily disposables
-reusable lenses that consist of 2-weekly, monthly and planned replacement
what are the advantages to contact lenses?
-contacts stay in place unlike glasses which can slip down and fog up
-give you a wider fov than spectacles
-comfortable to wear without the weight of glasses
-good for an active lifestyle
what are the cons of CLs?
-can be expensive
-need to be removed before sleeping
-cant be worn when showering or swimming
-take time to adjust at the start
-can cause dry eye
-can increase risk of ocular infections
what are the stages of the CL fitting patient journey?
-initial fitting appointment
-teach
-CL trial
-aftercare of (CL check, check-up and follow up)
what do you do as the practitioner in the initial contact lens fitting
-ask about details of the medical and ocular history
-ask details about needs and expectations of CL wear
-look at their spectacle prescription
-examine the anterior eye and tear film
what is the point of the initial CL fitting appointment?
-discuss the contact lens options w the patient to make informed choice
-advise if they are unsuitable for CLs
-record this info on the patient record
What happens in the patient teach?
-show patient how to apply and remove their lenses
-explain how to wear and care for lenses
-explain the wearing and replacement schedule
-advise the patient what to do if they have a problem
-record the advice given on the patient record
-arrane the follow-up appointment
-give the patient a written copy of the advice
what happens in the CL trial?
the patient takes the CLs to trial them for a short period of time. allows patients to ensure the lenses are meeting their needs and expectations
what happens in CL aftercare check?
-discuss how the lenses performed compared to the patients expectations
-ask about any problems experienced
-check the patients compliance
-check the VA and lens fit
-examine the anterior eye after removing the lenses
-record this info on the patient record
in contact lens aftercare, what do you if the lenses are not appropriate
a different lens could be fitted
in CL aftercare, how do you proceed of the lenses are appropriate?
the patient is issued with the CL spec and can buy lenses from the practise, another practise or online up to the expiry date
what happens after the intial aftercare?
the patient attends regular aftercare and can purchase lenses until the CL spec expires
What are the most common contact lens complications?
discomfort, vision problems and redness and these just increase risk of contact lens dropout
what is a serious infection that CLs increase the risk of?
microbial keratitis (MK)
how many people get MK for
-daily soft wearers
-overnight soft lens wearers
-2-4 per 10,000 wearers per year for daily soft lens wearers
-20 per 10,000 wearers per year for overnight soft lens wearers
what are the main risk factors for MK?
-poor hygiene
-overnight wear
what is MK?
inflammation of cornea through direct infection from the microbial agent being bacteria, virus, fungus, protozoa
what % of acanthamoeba keratitis (AK) occurs in CL wearers?
85%
what is AK and what are the risk factors?
a rare but very serious form of MK
-swimming, showering in lenses
-contamination from tap water
what are the steps to advise applying lenses?
- clean dry hands
- remove lens from packaging/CL case and inspect
- lid positioning
- place lens directly onto cornea
What are the steps to advise for lens removal
- clean, dry hands
- lid postitioning
- drag lens away from cornea and pinch off
- discard the lens if its a daily disposable
5 clean the lens with solution NOT WATER, if it is reusable
what do you tell a patient when explaining how to wear and care for lenses?
-reinforce the importance of hygiene and compliance so no water contamination and no sleeping in the lenses
-prevent lens contamination so makeup, water and eye drops
-only use prescribed lenses and recommended care solutions
-attend regular appointments as problems can occur without symptoms
what do you tell a patient in case they have a problem with their CLs?
-have a daily checklist, do your eyes feel well, see well and look well, if in doubt take them out
-remove lenses immediately if problems occur and contact the practitioner
-do not resume lens wear until checked
-provide practise phone number and advise what to do out of hours
how long after the trial appt of the CLs should you arrange a follow up?
1-2 weeks after the teach
what should you tell the patient to bring to the follow up appointment?
-the patient should come in wearing their CLs
-bring their glasses
-bring their CL case is the lenses are reusable
what are the three methods used to make CLs?
-lathing
-spin casting
-moulding
what are the names used to describe soft contact lenses?
-HEMA
-PHEMA
-poly HEMA
what two materials start off contact lens manufacture?
-polymer
-liquid monomer
how is the material of polymer prepped for CL manufacture?
- anhydrous material in rod form is sliced into buttons
- button is shaped then hydrated to form the lens
how is liquid monomer material prepped for soft CL manufacture?
- injected into a mould
- polymerisation
- hydration
how are soft CLs made through lathing?
- polymer button mounted onto brass tools
- lathed with diamond tipped tool
- back (concave) surface is lathed, diameter is cut down to the required size
- button is transferred and front convex surface is lathed
- lens is polished to remove lathe marks
- lens is inspected and hydrated
- inspected, packaged, autoclaved and labelled
What are the advantages to lathing?
-relatively simple
-wide range or parameters
-relatively inexpensive to start production
what are the disadvantages to lathing?
-complex designs are difficult
-labour intensive
-high cost per lens
-variable surface finish
-relatively slow
-hard to produce in large volumes
-reproducibility is hard
What are the steps used to produce soft CLs with spin casting?
- convex stainless steel tool (male) used to create a disposable plastic concave (female) mould
- liquid monomer is introduced to the rotating concave female
- centrifugal forces distribute the monomer across the mould
- polymerisation via UV and or heat cure occurs at the same time to produce the lens
- the lens edge is polished if necessary
- lens is inspected and hydrated
- inspection, blister package and autoclaved
what are the advantages of spin casting?
-higher volume manufacture compared to lathing
-automated production
-low cost per lens
-rapid
-volume production is relatively easy
what are the disadvantages of spin casting?
-expensive to start production
-expense limits parameter range
-lens edge may need further finishing
-poorer reproducibility than moulding
-lower volume than moulding gets produced
what are the steps in moulding to make soft CLs?
- stainless steel male and female tool used to create disposable plastic moulds
- liquid monomer introduced between moulds and cured (UV/ heat)
- inspected and hydrated
- inspected, blister packaged and autoclaved
what are the positives to using moulding to manufacture hydrogels?
-high volume manufacture
-automated production
-low cost per lens
-volume production is easy
-good surface quality
-good reproducibility
what are the disadvantages to moulding?
-expensive to start production
-expense limits parameter range
what should you explain to patients to make them aware of the environmental impact of CLs?
-the environmental impact of lens manufacture
-annualised waste of different wearing modalities
-recycling options
In what ways can the polymer chain be modified to change the physical characteristics of the plastic that will make the CL?
-long chain structure creates toughness and elasticity
-interaction of polymer chains gives resultant characteristic physical properties
-increased stability is achieved by cross linking polymer chains
What are the three types of materials used to make soft CLs?
-standard hydrogel
-silicone hydrogel (high oxygen permeability)
-water gradient materials (in between standard hydrogel and silicone hydrogel)
why are co polymers added to pHEMA CLs?
-to increase their water content and so increase the oxygen permeability
-to alter their wettability
-to alter their modulus
-to alter their ionicity
give some common copolymers
-PVA: polyvinyl alcohol
-PVP: polyvinyl pyrrolidone
-MMA: methyl methacrylate
what methods do manufacturers use to enhance lens comfort?
-packaging additives such as surfactants
-lubricants and wetting agents bound to lens materials
-lubricants and wetting agents released from lens material
for packaging additives,
-give examples
-how they advance CL comfort
-HMPC and PVP
-have a cushion effect upon insertion
for lubricants and wetting agents bound to lens material:
-give examples
-how they advance CL comfort
-pvp and PEG
-maintain wettability and reduce dehyrdation
for lubricants and wetting agents released from lens material:
-give examples
-how they advance CL comfort
-PVA
-‘time release’ / ‘blink activated’
what are the advantages of having hydrogels with high water content?
-have greater oxygen permeability
-less hypoxia
-hydrophillic surface
-softer so lower modulus and less stiff
what are the disadvantages of having hydrogels with a high water content?
-greater tendancy to dehydrate
-greater deposition
-difficult handling
-fragile and easy to tear
-difficult to manufacture
-must be made thicker to compensate
what is silicone?
an organic compound made of silicon and oxygen
why use siicone hydrogels?
as they offer greater oxygen performance compared to hydrogels as oxygen is more soluble in silicone than in water and so oxygen passage is no longer dependent on the water content
why do silicone hydrogels first need to be modified?
As silicone is inherently hydrophobic and so lenses need to be modified to make the surface hydrophillic and wettable
what are the three types of material modification that determine the generation of the silicone hydrogel?
-surface treatment
-internal wetting agent
-polymer
what is the definition of a biomaterial?
a natural or synthetic material that is suitable for introduction into living tissues, especially as part of a medical device
what are the bulk properties of CLs?
water content, oxygen permeability, density, dimensional stability, uv blocking, tensile strength, tear strength and modulus of rigidity
what are the surface properties of CLs?
wettability, coefficient of friction/ lubricity, ionicity, deposition and microbial adherence
what are the optical properties of CLs?
refractive index, optical transmittance
what is the range of WC (water content) range in soft CLs?
24-79%