Considering Needs & Fitting Contact Lenses Flashcards
Rules for fitting contact lenses
- Only registered optometrists, contact lens opticians and doctors can fit lenses
- Patients wishing to wear powered contact lenses must have had a recent sight test (within two years, or earlier if an earlier date is specified on the patient’s prescription).
- You should discuss options with patients to help them make informed choices
- You must record all the relevant information in the patient notes.
- You must provide the patient with appropriate advice and written information to wear, clean and maintain their lenses.
- When the fitting is complete you must give the patient their contact lens specification
What should a contact lens specification include
- The name and address of the individual
- If the individual has not attained the age of sixteen on the day the specification is issued, his date of birth
- The name and registration number of the person signing the specification
- The address from which the person signing the specification practises
- The name of the practice on whose premises the fitting was done
- The date the fitting was completed
- Sufficient details of any lens fitted to enable a person who fits or supplies a contact lens to replicate the lens
- The date the specification expires
- Such information of a clinical nature as the person fitting the lens considers to be necessary in the particular ca
Most common reasons for discontinuation of contact lenses
- Discomfort
- Problems with vision
- Handling problems
- Dry/watering/red eyes
- Infection
- Difficulties applying/removing lenses
Identification of needs in contact lenses
- Relates to lifestyle
- Consider lens features
- Outside activities – UV
- Critical vision – details in near or distance
- Hygiene limitations
- Comfort
Advantage of silicon hydrogel
Comfortable
Advantage of RGPs
- Good vision
- Correct astigmatism better for clarity of vision
Modality and features
- Daily – expensive
- 2 Weekly/Monthly
- Annual
- UV Block / Wettability agents
Which is more expensive - daily or monthly
Dailys
Why might reduced oxygen be an issue
Might get encroachment of vessels = neovascularisation
What is the Dk/t for daily lenses and extended wear lenses
- Daily Wear = 0% = No corneal swelling = Dk/t 37
- Extended Wear = 4% Corneal Swelling ( because that 4% happens naturally when sleep even when not wearing lenses ) = Dk/t 125
Why do we get more corneal swelling in extended wear lenses
Because that 4% happens naturally when sleep even when not wearing lenses
Daily wear lenses compared to extended wear lenses
- Daily wear = higher Dk/t and no corneal swelling
- But corneal swelling is present in EW lenses
Limitations of Dk/t
- Generally quoted for a prescription of -3.00
- ACLM quotes the Dk of the material
- Lenses are not a uniform shape
Dk/t in hydrogels
The theoretical maximum Dk/t is 40 but the reality is 22-28
Dk/t in silicone hydrogels
Dk/t values tend to be from 40-160, typically around the 100-130 region :(
What should and shouldn’t we consider in silicone hydrogel lenses
- Oxygen should not be a concern when considering daily wear in Silicone Hydrogels
- More important to consider mechanical issues, tear exchange and what to do if there is irritation cause they have less water in them than hydrogels
What should we consider in high rx lenses
Oxygen in the centre and periphery – look for hyperaemia or neovascularisation which shows less o2 present
Water content of a lens
- Low – approx. 35-40%
- Medium – 50-55%
- High -65%+
What does water content of a lens relate to
Oxygen transmission in hydrogels
What does water content of a lens effect
- Changes how flexible a lens is
- More water in a lens – more flexible AND the more O2 it can transmit through the water
Water content in silicone hydrogels vs hydrogels
- In hydrogels, water is the way eye gets o2 so more water = more o2
- But in silicone hydrogels, the water can get through the silicone part of the lens not just water
Water content of RGP lens
0 = rigid
Reason for dry eyes:
- Lack fluid i.e aqueous deficient
- Poor air quality – tears dry out too quickly – low TBUT
What is TBUT in dry eyes
Low
What effect does water content have on a patient with dry eyes?
- Lenses have certain % of water e.g. 50%
- If px has dry eye and they put lenses in, if have 80% water that is a soft lens.
- If its high water content, i.e when person puts the lens in first, it will feel nice because lots of fluid low rigidity
-But over time lens dry out due to natural evaporation - And that lens is designed to hold that certain % of water
- So if it drops in % of water through natural drying out, it acts like a sponge and reabsorb more fluid
- Get that fluid from tears
- So if px already has dry eyes, over the day the lens dries out and more of it gets soaked up and reabsorbs tears in eyes
- So end of day discomfort bad
- Low water content lens may be better for px with dry eyes because less water to evaporate from the lens
What is modulus of lens
- How well a material resists deformation and application of pressure
- It’s a property of the material not the contact lens design – shape and form
What does modulus depend on
Depends on thickness and shape
Modulus of daily lenses vs monthly lenses
- Daily lenses thinner – more flexible
- Monthly – thicker – stiffer handling cause more material in the lens
Modulus of hydrogel lenses
- Typically in the 0.3-0.5 range
- Lower modulus = more comfortable
Modulus of some lenses
- B&L – Purevision = 1.10
- Alcon – Air Optix = 1.00
- Coopervision – Avaira = 0.50
- J&J – Acuvue Oasys = 0.72
When would you stress about oxygen in lenses
- High rx
- More extensive wear times
