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Contact Lenses > Considering Needs & Fitting Contact Lenses > Flashcards

Considering Needs & Fitting Contact Lenses Flashcards

1
Q

Rules for fitting contact lenses

A
  • 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
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2
Q

What should a contact lens specification include

A
  • 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
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3
Q

Most common reasons for discontinuation of contact lenses

A
  • Discomfort
  • Problems with vision
  • Handling problems
  • Dry/watering/red eyes
  • Infection
  • Difficulties applying/removing lenses
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4
Q

Identification of needs in contact lenses

A
  • Relates to lifestyle
  • Consider lens features
  • Outside activities – UV
  • Critical vision – details in near or distance
  • Hygiene limitations
  • Comfort
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5
Q

Advantage of silicon hydrogel

A

Comfortable

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6
Q

Advantage of RGPs

A
  • Good vision
  • Correct astigmatism better for clarity of vision
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7
Q

Modality and features

A
  • Daily – expensive
  • 2 Weekly/Monthly
  • Annual
  • UV Block / Wettability agents
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8
Q

Which is more expensive - daily or monthly

A

Dailys

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9
Q

Why might reduced oxygen be an issue

A

Might get encroachment of vessels = neovascularisation

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10
Q

What is the Dk/t for daily lenses and extended wear lenses

A
  • 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
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11
Q

Why do we get more corneal swelling in extended wear lenses

A

Because that 4% happens naturally when sleep even when not wearing lenses

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12
Q

Daily wear lenses compared to extended wear lenses

A
  • Daily wear = higher Dk/t and no corneal swelling
  • But corneal swelling is present in EW lenses
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13
Q

Limitations of Dk/t

A
  • Generally quoted for a prescription of -3.00
  • ACLM quotes the Dk of the material
  • Lenses are not a uniform shape
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14
Q

Dk/t in hydrogels

A

The theoretical maximum Dk/t is 40 but the reality is 22-28

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15
Q

Dk/t in silicone hydrogels

A

Dk/t values tend to be from 40-160, typically around the 100-130 region :(

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16
Q

What should and shouldn’t we consider in silicone hydrogel lenses

A
  • 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
17
Q

What should we consider in high rx lenses

A

Oxygen in the centre and periphery – look for hyperaemia or neovascularisation which shows less o2 present

18
Q

Water content of a lens

A
  • Low – approx. 35-40%
  • Medium – 50-55%
  • High -65%+
19
Q

What does water content of a lens relate to

A

Oxygen transmission in hydrogels

20
Q

What does water content of a lens effect

A
  • Changes how flexible a lens is
  • More water in a lens – more flexible AND the more O2 it can transmit through the water
21
Q

Water content in silicone hydrogels vs hydrogels

A
  • 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
22
Q

Water content of RGP lens

A

0 = rigid

23
Q

Reason for dry eyes:

A
  • Lack fluid i.e aqueous deficient
  • Poor air quality – tears dry out too quickly – low TBUT
24
Q

What is TBUT in dry eyes

A

Low

25
Q

What effect does water content have on a patient with dry eyes?

A
  • 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
26
Q

What is modulus of lens

A
  • 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
27
Q

What does modulus depend on

A

Depends on thickness and shape

28
Q

Modulus of daily lenses vs monthly lenses

A
  • Daily lenses thinner – more flexible
  • Monthly – thicker – stiffer handling cause more material in the lens
29
Q

Modulus of hydrogel lenses

A
  • Typically in the 0.3-0.5 range
  • Lower modulus = more comfortable
30
Q

Modulus of some lenses

A
  • B&L – Purevision = 1.10
  • Alcon – Air Optix = 1.00
  • Coopervision – Avaira = 0.50
  • J&J – Acuvue Oasys = 0.72
31
Q

When would you stress about oxygen in lenses

A
  • High rx
  • More extensive wear times

Contact Lenses (8 decks)

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