UNIT 4: Astigmatism & Presbyopia

Question 1

Types of Astigmatism: Corneal

Answer 1

• 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

Question 2

Astigmatism By Meridian

Answer 2

Question 3

Total/ Refractive Astigmatism

Answer 3

• 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

Question 4

Residual Astigmatism

Answer 4

• 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.

Question 5

Calculating Residual Astigmatism

Answer 5

• 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

Question 6

Soft Lens Correction

Answer 6

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

Question 7

Soft Toric Stabilization

Answer 7

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

Question 8

Soft Toric Lens Fitting

Answer 8

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

Question 9

Soft Toric Lens Evaluation

Answer 9

• Movement
• Axis Rotation
• V/A
• Comfort

Question 10

Soft Toric Lens Problems

Answer 10

• Discomfort
• Axis Mislocation
• Edema
• V/A

Question 11

Rigid Lens Correction

Answer 11

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

Question 12

Fitting Front Surface Torics

Answer 12

• 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

Question 13

Fitting Back Surface Torics

Answer 13

• 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

Question 14

Fitting Bitoric Lenses

Answer 14

• 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

Question 15

Presbyopic Contact Lens Fitting: Distance Vision with Readers

Answer 15

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

Question 16

Presbyopic Contact Lens Fitting: Monovision

Answer 16

• 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

Question 17

Presbyopic Contact Lens Fitting: Bifocal

Answer 17

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

Question 18

Presbyopic Patients Wearing Contact Lenses (CL Spectrum)

Answer 18

• 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

Question 19

Patient Selection

Answer 19

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

Question 20

Lid Position & Pupil Size

Answer 20

Question 21

Lid Position & Pupil Size

Answer 21

Question 22

Pre- Corneal Film Assessment

Answer 22

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

Question 23

Tear Break Up Time

Answer 23

Question 24

Corneal Dryness

Answer 24

Question 25

Cornea: Keratitis Sicca

Answer 25

- 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

Question 26

Keratitis Sicca with Rose Bengal

Answer 26

Question 27

Types of Bifocals: Visual Mechanism Simultaneous

Answer 27

- 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.

Question 28

Types of Bifocals: Visual Mechanism - Alternating/ Translating

Answer 28

- 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.

Question 29

Cast Molded Advantages & Disadvantages

Answer 29

- Advantages: - Lower unit cost - Surface quality - Reproducibility - Disadvantages: - Initial set-up costs - Limited parameters - Edge finish

Question 30

Types of Bifocals: Lens Designs- Segmental/ Alternating

Answer 30

- 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

Question 31

Triton Gelflex

Answer 31

Question 32

Segmental/ Alternating: Truncation

Answer 32