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Clinical Skills > Contact Lenses Types and Fitting Measurements > Flashcards

Contact Lenses Types and Fitting Measurements Flashcards

1
Q

What are the types of contact lenses

A
  • Rigid Gas Permeable ( RGP )
  • Soft Contact Lenses
  • Speciality
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2
Q

What are RGP lenses

A
  • Made up of solid plastic
  • Approx 9mm diameter
  • Reusable ( 1 to 3 ) years
  • Clean after each wear
  • More comfortable
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3
Q

What are soft contact lenses

A
  • Approx 14mm diameter

- Disposable or reusable

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4
Q

What are speciality contact lenses

A
  • Re - usable

- For certain eye conditions

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5
Q

What is meant by the term modality

A

How someone wears contact lenses

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6
Q

Replacement for Soft lenses

A
  • Daily disposable
  • 2 - weekly
  • Monthly disposables
  • Annual
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7
Q

Replacement for RGP

A
  • Replacement every 1-3 years
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8
Q

Wear modality for Soft lenses

A
  • Daily (Daily Wear)
  • 7 days and 6 nights ( Extended wear )
  • 30 days and 29 nights ( Continuous wear - don’t take it out = not recommended )
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9
Q

Wear modality for RGP lenses

A
  • Daily (DW)

Overnight ( only with keratology)

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10
Q

Are there dailys/monthlys for RGP lenses

A

No

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11
Q

How do daily disposables work

A

Throw away at end of the day - no cleaning

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12
Q

What are the type of prescriptions for CL’S

A
  • Spherical
  • Toric
  • Multifocal
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13
Q

What are spherical lenses for

A

Myopia/hypermetropia

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14
Q

What are toric lenses for

A

Asitgmatism

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15
Q

What are multifocal lenses for

A

Varifocal - presbyopia

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16
Q

Which contact lens rx is most common

A

Spherical soft - vast majority

Then toric soft

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17
Q

What are the different types of materials for CL’s

A
  • Rigid lenses - PMMA and GP

- Soft lenses - Hydrogel and Silicone hydrogel

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18
Q

What are PMMA lenses

A
  • Rigid lens
  • Very first
  • No O2 permiability
  • Excellent vision
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19
Q

What are Gas Permeable lenses

A
  • Much better O2 permeability - healthier
20
Q

What are hydrogel soft lenses

A
  • Contains water - transports O2

- Very comfortable

21
Q

What are silicone hydrogel lenses

A
  • Hydrogel with Silicone in it
  • More oxygen than hydrogel
  • More expensive
  • Allow to use for extended wear/ continuous wear
22
Q

What are the baseline measurements for CL’s

A
  • Spectacle rx - convert to ocular rx
  • Measure curvature of cornea - keratometry
  • Measure diameter of cornea - size of eye
23
Q

How to measure diameter of cornea

A

Horizontal Visible Iris Diameter….
Measure iris size - cornea diameter
Its hard to measure cornea cause its clear

24
Q

What is ocular rx

A

The rx for CL’s

25
Q

What is back vertex

A

How far away glasses sit from eye

If gap changes the power has to change as well

26
Q

What is the Back Vertex Distance

A

Its used to convert the rx using the vertex distance and back distance.
Only for rx 4.00 and above

27
Q

What is astigmatism

A

2 focal points at back of eye, 1 on meridian and 1 on other meridian
Imperfection in the curvature of ocular cornea and/or crystalline lens

28
Q

How do you correct astigmatism

A

Use two different rx’s simultaneously in principle meridians

29
Q

What 2 places are astigmatism created

A
  • Cornea - front surface (might be more curved one way and not so curved other way )
  • In crystalline lens
30
Q

What are principle meridians

A

Powers - different directions

31
Q

What is regular meridians

A

Whatever one meridian is, other meridian is 90 degrees to it.
E.g. 1st meridian - 10 degrees
2nd meridian - 100 degrees ( 10 + 90)

32
Q

What is irregular meridian

A

The difference between the 1st and 2nd meridians is NOT 90 degrees apart
Due to trauma, disease e.t.c

33
Q

What value does meridian have to be between

A

0 and 180

34
Q

What does astigmatic spectacle rx cause

A

Blur - different powers in two principle meridians

35
Q

Symptoms of Astigmatism

A
  • Blurry vision
  • Fatigue or eye strain
  • Distorted vision
  • Light sensitivity
  • Excessive squinting
  • Headaches
36
Q

What are the types of corneal astigmatism

A
  • With the Rule

- Against the Rule

37
Q

What is With the Rule astigmatism

A

The vertical meridian is steeper ( more curved ) than the horizontal meridian. Flatter horizontal way

38
Q

What is Against the Rule astigmatism

A
  • The horizontal meridian is steeper ( more curved ) than the vertical meridian
    Flatter vertical meridian
39
Q

What is the rules for choosing the rx

A

SPHERE: most positive
CYL: difference between two powers
AXIS: Orientation of the more positive power

40
Q

What does along mean for CL’s

A

In that direction vertical

41
Q

What is meant by keratometry

A

The measurement of the principle radii of the anterior surface of the cornea ( tear film )

42
Q

How does karatometry work

A 
The cornea ( tears ) acts as a mirror since light is reflected from it - measure radius of curvature of this ' mirror'
Gives you principle meridian powers
43
Q

Why do keratometry

A

Determination of…..

  • Central Corneal Radius and and power in both principle meridians of cornea
  • Differentiate between regular and irregular astimgatism
  • Observe quality of tears and reflected mires
  • Measure NIBUT ( non - invasive break up time )
  • Measurement of radius of contact lenses
44
Q

What do you always round the power nearest to

A

0.25D

45
Q

What is radius rounded closest to

A

0.05MM

46
Q

What does curvature correlate to

A

Certain corneal power

47
Q

Horizontal Visible Iris Diameter….

A

Why… for total diameter CL
Measure with PD rule
Expected 11.6mm ( between 10.2-13.0mm)

Clinical Skills (6 decks)

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