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OPT 2501 Contact Lens Theory 2 > UNIT 4: Astigmatism & Presbyopia > Flashcards

UNIT 4: Astigmatism & Presbyopia Flashcards

1
Q

Types of Astigmatism: Corneal

A
  • Regular: Meridians 90 Degrees Apart
    • WTR: Flattest K @ 180 Degrees ( +/- 30 Degrees)
      Example: 41.00@180/43.00@90
    • ATR: Flattest K @ 90 Degrees ( +/- 30 Degrees)
      Example: 45.00@180/42.00@90
    • Oblique: Flattest K between 30&60 or 120&150
      degrees
      Example: 42.50@35/44.75@125
  • Irregular: Flattest & steepest meridians are
    notably more or less than 90 degrees apart.
    Example: 41.00@180/42.00@60
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2
Q

Astigmatism By Meridian

A
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3
Q

Total/ Refractive Astigmatism

A
  • The amount of astigmatism in the spectacle
    prescription. It represents the combined effect of
    the cornea and internal astigmatism.
  • Minus cylinder axis 180 (+/- 30 degrees) corrects
    WTR astigmatism.
    Example: -3.00 -1.00 x 180
  • Minus cylinder axis 90 (+/- 30 degrees) corrects
    ATR astigmatism.
    Example: -3.00 -1.00 x 90
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4
Q

Residual Astigmatism

A
  • Astigmatism that remains after a contact lens
    is fit to the cornea.
  • Spherical rigid lenses will neutralize corneal
    astigmatism with the tear layer behind the lens.
    Any internal astigmatism will remain and may
    create optical problems.
  • Soft lenses conform to the cornea and do not
    neutralize corneal astigmatism.
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5
Q

Calculating Residual Astigmatism

A
  • The amount of residual astigmatism may be
    calculated by comparing the “K” readings to the
    spectacle prescription in minus cylinder form.
  • With the spectacle prescription in minus cylinder
    form determines the amount and type of
    refractive astigmatism.
  • If they are both the same type ( WTR, ATR,
    Oblique) subtracts refractive astigmatism for
    the corneal astigmatism.
    Example: “K”:41.50@180/43.50@90 = 2.00D WTR
    RX: -3.50 -1.50x180 = 1.50D WRT
    ____________
    0.50 CRA
  • If they are opposite types ( WTR, ATR,
    Oblique) add refractive astigmatism for
    the corneal astigmatism.
    Example: “K”:41.50@180/43.50@90 = 2.00D WTR
    RX: -3.50 -1.50x090 = 1.50D ATR
    ____________
    3.50 CRA
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6
Q

Soft Lens Correction

A
  • Spherical:
    • Rx Astigamtism =/< 1.00D
    • Rx Sphere to Cyl. Ratio >/= 3 to 1
  • Toric Designs:
    • Front surface
    • Back surface
    • Stock
    • Custom
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7
Q

Soft Toric Stabilization

A
  • Prism Ballast
  • Truncation
  • Double slab off/ Thick&thin zones
  • Posterior Toric
  • Aspheric Posterior
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8
Q

Soft Toric Lens Fitting

A
  • Patient selection
  • Lens selection
  • Insertion and Equilibration
  • Lens Evaluation
  • Axial Alignment
  • Compensation ( LARS )
  • Order
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9
Q

Soft Toric Lens Evaluation

A
  • Movement
  • Axis Rotation
  • V/A
  • Comfort
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10
Q

Soft Toric Lens Problems

A
  • Discomfort
  • Axis Mislocation
  • Edema
  • V/A
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11
Q

Rigid Lens Correction

A
  • Spherical:
    • Residual Astigmatism </= 1.00D
    • Corneal Astigmatism < 3.00D
  • Toric Designs:
    • Front Surface
    • Back Surface
    • Bitoric
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12
Q

Fitting Front Surface Torics

A
  • Select spherical diagnostic lens 0.75 - 1.5^
  • Evaluate fluorescein pattern & axis
  • Sphero-cyl overrafracion
  • Add overrafraction to diagnostic lens
    power and compensate for rotation
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13
Q

Fitting Back Surface Torics

A
  • Rigid contact lens index of refraction = 1.49
    versus Cornea = 1.375
  • Approx: 2/3 of the corneal toricity may be placed
    on the posterior lens surface
  • K’s: 42.00/45.00@90
  • Rx: -2.00 - 3.00 x 180
  • CPC = 42.00 x 44.00
  • Power -2.00 -3.00 x 180
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14
Q

Fitting Bitoric Lenses

A
  • Calculate CPC and Power for each meridian
    separately.
  • Fit the flattest meridian CPC 0.25 D flatter than
    flat “K”. Fit the steepest meridian 0.50 to 0.75D
    flatter than steepest “K”.
  • Determine the total power in each meridian.
    Compensate of the power is > 4.00D
  • Use FAP rule to adjust power
  • Order each meridian separately
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15
Q

Presbyopic Contact Lens Fitting: Distance Vision with Readers

A
  • Advantages:
    • No lens design or material limitations
    • Good vision possible at all distances
  • Disadvantages:
    • Does not fulfill cosmetic needs
    • Inconvenient
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16
Q

Presbyopic Contact Lens Fitting: Monovision

A
  • Advantages:
    • No lens design or material limitations
    • Inexpensive
    • Can be worn part-time
  • Disadvantages:
    • Loss of depth perception
    • Headaches
    • Limited success with higher add powers
    • Prolonged near work difficult
17
Q

Presbyopic Contact Lens Fitting: Bifocal

A
  • Advantages:
    • Binocular distance and near correction
    • Fulfills patient’s cosmetic needs
  • Disadvantages:
    • Cost
    • Success Rate
18
Q

Presbyopic Patients Wearing Contact Lenses (CL Spectrum)

A
  • Practitioner preference for presbyopic contact
    lens patients:
    • 59% multifocals
    • 27% Monovision
    • 14% Over-Spectacles
  • In practice, Presbyopic Patients:
    • 66% Glasses
    • 16% Monovision CL
    • 15% Soft Multifocal CL
    • 3% GP Multifocal CL
19
Q

Patient Selection

A
  • Motivation
  • Visual Demand
  • Astigmatism
  • Intended Use
  • Distance Rx and Add Power
  • Lid Position
  • Tear Quality & Quantity
  • Pupil Size/ Change in Size
20
Q

Lid Position & Pupil Size

21
Q

Lid Position & Pupil Size

22
Q

Pre- Corneal Film Assessment

A
  • Schirmer Test
  • Break Up Test (B.U.T.)
  • Rose Bengal
  • Lacrimal Lake
23
Q

Tear Break Up Time

24
Q

Corneal Dryness

25
Cornea: Keratitis Sicca
- Keratoconjunctivitis Sicca - Several Possible causes: - Reduced function of lacrimal glands - Excessive evaporation of tears - Mucin deficiency - Tests: - Rose Bengal, Schirmer - B.U.T. - Lacrimal Lake
26
Keratitis Sicca with Rose Bengal
27
Types of Bifocals: Visual Mechanism Simultaneous
- Light passes through distance & near portions simultaneously. - Two bundles of light contribute to the retinal image at all times. - Patient learns to ignore one and concentrate on the other.
28
Types of Bifocals: Visual Mechanism - Alternating/ Translating
- Wearer uses one portion of the lens for distance vision and another portion for near vision. - As the eye moves down to read the lower lid moves the CL up, so that the reading segment lies in the pupillary area. - Truncation and/or prism is usually required to stabilize lens rotation.
29
Cast Molded Advantages & Disadvantages
- Advantages: - Lower unit cost - Surface quality - Reproducibility - Disadvantages: - Initial set-up costs - Limited parameters - Edge finish
30
Types of Bifocals: Lens Designs- Segmental/ Alternating
- Advantages: - Clearer image higher add powers - Disadvantages: - Must translate, comfort problems, Edema - Examples: - Tangent Streak (GP) - Firestone Optics - Solitaire (GP) - Truform Optics - Solution (GP) - XCell - Trition (Soft) - Gelflex
31
Triton Gelflex
32
Segmental/ Alternating: Truncation

OPT 2501 Contact Lens Theory 2 (4 decks)

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