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Contact Lenses - Year 2 > SCL Fitting 1 > Flashcards

SCL Fitting 1 Flashcards

1
Q

On what basis are RGPs replaced?

A

Replacement every 1-3 years or earlier if scratched

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2
Q

On what basis are soft contact lenses replaced?

A

Depending on the type they are:

– Daily disposables (DW)

– Bi-weekly or Monthly disposables (EW)

[EW- extended wear]

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3
Q

What is a daily disposible lens?

A

FDA definition: a lens replaced after each use (i.e. remove and discard)

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4
Q

What are examples of daily soft contact lenses?

A
  • Acuvue 1-Day Moist
  • Dailies Aqua Comfort Plus
  • Biotrue ONEday
  • Proclear 1 Day
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5
Q

What are examples of Bi-weekly replacement soft contact lenses?

A
  • Acuvue 2
  • Acuvue Oasys
  • Avaira
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6
Q

What are examples of monthly soft contact lenses?

A
  • Air Optix Aqua
  • Proclear, Frequency 55
  • Biofinity
  • Air Optix Night & Day
  • Purevision 2
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7
Q

In the UK, which is the most popular type of contact lens, SCL or RGP?

A

SCL

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8
Q

What factors are driving the growth of the SCL market?

A

Growing rate of myopia

Growing Geriatric population

Increasing preference fo contact lenses

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9
Q

What factors are hindering the growth of the SCL market?

A

Unregulated online sales

Regulatory barriers concerning contact lens sale

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10
Q

What was the first soft hydrogel contact lens material?

A

HEMA (in 1970).

[It continues to be the monomer most often utilised]

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11
Q

Is HEMA very stable or unstable of a material?

A

Very stable - variations in temperature, ph, etc have vewry little effect on it

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12
Q

Is HEMA a comfortable lens material?

A

Yes

[It contains water and transports O2]

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13
Q

True or false- HEMA has good wetability

A

True

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14
Q

True or False- Silicone hydrogels allow for less oxygen transmission than HEMA based contact lenses

A

False - SiH CLs allow for more oxygen transmission

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15
Q

Which are more expensive HEMA (hydrogel) Lenses or SiH (Silicone hydrogel) lenses?

A

Silicone Hydrogel lenses

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16
Q

How does wetability affect comfort?

A

Wetability aides the closure of the lid over the lens thereby improving comfort and preventing changes to the papillary surface (of inner eyelid).

A very wetable surface creates an even stable tearfilm optimsing comfort, visual acuity and resistance against deposits.

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17
Q

What does it mean to have no net increase in the amount of contact lens wearers?

A

It means that for every new contact lens wearer there is an old contact lens wearer that discontinues use

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18
Q

What is a material’s modulus?

A

A value that expresses a material’s ability to keep its shape against stress, and resistance to deformation.

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19
Q

What are the properties of materials with a higher modulus?

A

They are stiffer, resist deformation, hold their shape better, are easier to handle and may provide better VA.

[Stiffer lenses though may have adverse effects as they cause an edge lift and can cause a SEAL, they can cause mucin balls or CLPC (Contact Lens Papillary Conjunctivitis)]

20
Q

What is the relationship between sleeping in contact lenses and eye infections?

A

Sleeping in contact lenses makes you 8 times as likely to develop an eye infection

21
Q

What are the strict rules regarding contact lenses and water?

A

Don’t ever bath, shower or swim in contact lenses!

22
Q

List some indications for fitting Soft Contact Lenses

A
23
Q

What are the main contra-indications for use of Soft Contact lenses?

A

Highlighted in red + pregnancy

24
Q

What are the two possible care regimes for soft contact lenses?

and what are the advantages of both?

A

You can use Multipurpose solutions or Hydrogen Peroxide

Multipurpose solutions:

  • These are Simple and convenient
  • And can be used for Cleaning, disinfecting, and storing
  • Method of use is to Clean, rub, rinse and store in (for min 4-6 hrs)

Hydrogen peroxide:

  • These are a Metallic disc in case or tablet to neutralise the disinfectant before wear
  • Px cannot have adverse reaction to preservatives
  • Gold standard?
25
Q

What are consequences of non-complaince of a Soft Contact Lens care regime?

A
  • Lens/case contamination
  • Increased lens deposits
  • Decreased comfort
  • Vision affected
  • Lens wear ‘drop out’
  • Serious complications
26
Q

What are the top reasons for contact lens px ceasing wear?

A

Too much effort to clean

Too expensive

Forget to order new supply in time

Not comfortable

Only worn for certain occasions

Prefer spectacles

27
Q

What may the base curve (BC) of SCL also be referred to as?

A

BOZR or BOR

[Back Optic Zone Radius or Back Optic Radius]

28
Q

What soft contact lens specifications are stated on the box?

A
29
Q

What BOZR do we choose for a soft contact lens?

A

On average 0.8mm flatter than the flattest K

The range is 0.6mm to 1.00mm flatter than the flattest K

30
Q

What does the BOZR we choose for a soft contact lens depend on?

A

Water Content and Diameter.

Contact lenses with a low water content need to be fitted a little bit flatter so 1.00mm flatter than the flattest k (KF+ 1.00m)

Contact lenses with a high water content need to be feeded 0.6mm flatter than the flattest K

  • Order flatter BOZR for smaller HVIDs (than average 11.8mm)
  • Order steeper BOZR for larger HVIDs
31
Q

How do we choose the total diameter for a Soft contact lenses?

A

~2mm larger than HVID

32
Q

What are british standards for the total diameter?

A

That it must be recorded to 2 dp

33
Q

What range of total diameters are available for soft contact lenses?

A

⊘ 13.80

⊘ 14.00

⊘ 14.20

⊘ 14.40

⊘ 14.50

34
Q

Why do we order the total diameter of a sofft contact lens to be 2mm larger than the HVID?

A

The lens should cover the cornea in primary gaze and in all positions of gaze – To avoid desiccation of exposed cornea

[Ideally the the lens should cover 0.5mm of the conjunctiva in all directions of gaze]

35
Q

How do you determine the BVP of a SCL?

A

Spectacle Rx = ocular (or contact lens) Rx

Unlesss power id >4.00D – In which case Use Vertex Distance Table,

or – K=Fsp/(1-(d*Fsp)) equation

, where • K=ocular refraction • Fsp=spectacle power • D=BVD in m

• You could also choose Mean spherical equivalent (sphere + ½ * cyl) if the cyl is less than -0.75 DC

Greater than -0.75DC onwards do not use MSE instead consider prescribing toric SCL

36
Q

After having taken history and symptoms and measurements what is the routine for fitting contact lenses on a px?

A
  1. Establish most optimum BOZR/TD BVP
  2. Pick trial lenses – Try different design/ manufacturer in each eye
  3. Assess fit and establish which lens is most comfortable for px
  4. Establish final choice – Same design/ manufacturer for both eyes
  5. Prescribe trial lenses for 5-7 days, book teaching session for insertion and removal, book follow up appointment to observe fit after 5 days
37
Q

What do you assess when judging the fit of a soft contact lens?

A

Physical fit:

  • Check it is Centred on-eye
  • Check Full coverage with versions (i.e. that it covers the cornea in all 8 positions of gaze)
  • Sufficient movement (this is needed to remove metabolic debris from the cornea) - (should not increase lens movement if you view signs of hypxia - you actually want to increase Dk/t of the material)
  • Check it Follows cornea and conjunctival curvature

Performance:

• Check PxComfort • Check for Stable vision

38
Q

What does a tightly fitted soft contact lens cause?

A

It won’t cause hypoxia.

(Steep RGP will though)

Can cause identationand press on conjunctival vessels,

If tears are stagnated in the limbal area , this will cause oxygen problems in that region.

39
Q

What is ‘Fluting’ and why is it bad?

A

When the edge of a soft contact lens stand off.

This is uncomfortable for the px

40
Q

What do we refer to a flat fit in SCL as?

A

A loose fit

41
Q

How can we change the base curve in order to adjust a SCL fit that is too loose?

A

Steepening the BC radius (8.60 to 8.30 mm) tightens the lens fit

[Unfortunately only one manufacturer, johnsons and johnsons, provides lenses in two base curves]

42
Q

How can we change the total diameter in order to adjust a SCL fit that is too loose?

A

Increasing the lens diameter (13.0 to 14.0 mm) tightens the lens fit , (reducing lens movement)

[This isn’t always possible though bc manufacturers don’t always make lenses in a variety of total diameters]

43
Q

What is more important for the comfort of a SCL px, the BC or the sag height?

A

Sag height is more important than BC for comfort

44
Q

What can the sagital height of the cornea/eye be predicted according to?

A

– the central corneal radius (keratometry)

– overall corneal diameter (most influential)

– corneal asphericity (important; e-value)

– the radius and asphericity of the para-limbal sclera

45
Q

A study in 2002 found that patients who had HVIDs between 11.6mm and 12.0mm had a high percentage of success using a traditional fitting approach (Kf +0.8mm)

• However, eyes that have a smaller HVID may need a _______ diameter or ______ base curve

A

However, eyes that have a smaller HVID may need a smaller diameter or flatter base curve

[The image shows 4 lenses that have the same BOZR - and how changing the total diameter affects the sag height and the fit]

46
Q

A study in 2002 found that patients who had HVIDs between 11.6mm and 12.0mm had a high percentage of success using a traditional fitting approach (Kf +0.8mm)

Eyes that have a larger HVID may require a ___________ diameter or ___________ base curve

A

Eyes that have a larger HVID may require a larger total diameter or steeper base curve

47
Q

To summarise what are the fitting rules for Soft Contact lenses?

A

Contact Lenses - Year 2 (18 decks)

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