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III. Advanced Contact Lenses > Irregular Cornea Fitting (M2) > Flashcards

Irregular Cornea Fitting (M2) Flashcards

1
Q

What are the possible causes of irregular astigmatism?

A
  1. keratoconus
  2. Pellucids marginal degeneration
  3. post penetrating keratoplasty
  4. post refractive surgery
  5. corneal/ocular trauma
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2
Q

What are the signs of keratoconus?

A
  1. irregular astigmatism
  2. Fleischer’s ring
  3. stromal thinning and scarring
  4. corneal steepening on topography
  5. Vogt’s striae
  6. Munson sign
  7. Charleaux sign
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3
Q

What is it called when iron deposits surround the base of a cone in keratoconus?

A

Fleischer’s ring

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4
Q

What are the stress lines that run parallel with the axis of the cone in the posterior stroma in keratoconus that disappear with gentle pressure?

A

Vogt’s striae

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5
Q

What is the sign of keratoconus in which there is a V shaped lower lid conformation in downgaze?

A

Munson sign

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6
Q

What is the sign of keratoconus where there is an oil droplet appearance with retroillumination?

A

Charleaux sign

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7
Q

What is the keratoconus complication in which breaks in Descemet’s membrane cause aqueous to come into the stroma that eventually results in scarring?

A

hydrops

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8
Q

What are the treatments for hydrops?

A
  1. topical antibiotics
  2. cycloplegics
  3. hypertonic solution
  4. nonsteroidal topical med
  5. steroid topical med
  6. bandage CL
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9
Q

Are steeper corneas in keratoconic patients fit flatter or steeper than flatter corneas?

A

flatter relative to flatter corneas

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10
Q

What lenses are generally used to maximize the vision in irregular cornea patients?

A

gas permeable with rigid material

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11
Q

What are the issues with wearing soft lenses for the correction of an irregular cornea?

A
  1. due to steepness of cornea, soft edge may result in fluting
  2. lens rotation and stability may not be consistent
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12
Q

What needs to be done for specialty soft CLs for irregular cornea patients to wear them?

A

increase center thickness

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13
Q

What is an example of a specialty soft keratoconus lens?

A

Kerasoft IC

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14
Q

What are different about the CLEK lens set lenses?

A
  1. steep BC
  2. small optic zone
  3. large peripheral widths
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15
Q

As a GP lens gets steeper, does the lens become more plus or minus? 1. The lacrimal lens? 2

A
  1. more minus

2. more plus

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16
Q

What are the parameters that are able to be changed in proprietary KCN lens designs? 1. What are some examples of these types of lenses? 2

A
  1. BC, OAD, power, PC’s

2. Rose K, CentraCone, Maguire, Dyna Z cone

17
Q

When are hybrid lenses good to use for irregular corneas?

A

intolerant to GPs but need GP optics

18
Q

What is a GP lens on top of a soft lens called?

A

piggyback

19
Q

What is the preferred type of soft lens to use while piggy backing?

A

prefer high Dk SiHy material with low modulus and plus lens can help center

20
Q

What should be done once the soft lens is fitted for piggybacking?

A

keratometry over soft CL to determine GP BC

21
Q

What type of fluorescein should be used to evaluate the GP fit during piggybacking?

A

high molecular weight fluorescein

22
Q

What are good conditions to use intralimbal GP lenses with large diameters?

A
  1. Pellucids MD

2. post PK

23
Q

Will a GP lens rest and attempt to center on the flattest or steepest part of the cornea?

A

steepest

24
Q

What are the possible desired fluorescein patterns for irregular cornea GP fitting (where is the weight of each lens?)?

A
  1. apical bearing (weight of lens on corneal apex)
  2. apical clearance (weight of lens on mid peripheral cornea)
  3. three point touch on steepest part and mid peripheral cornea (weight throughout cornea)
25
Q

Why do KCN GP lenses often have small optic zones and overall diameters?

A

large OZ diam with steep BC creates large sag depth which causes poor alignment of flatter areas of regular mid peripheral cornea

26
Q

What are the changes in peripheral curve radius that is clinically significant? 1. PC width? 2

A
  1. at least 1.0mm

2. at least 0.2mm

27
Q

What type of lens is able to create different PC throughout the lens?

A

ROSE K Asymmetric Corneal Technology

28
Q

Does corneal topography measure the elevation or curvature of the cornea?

A

curvature

29
Q

What is the equation to convert the radius of curvature into diopter power?

A

radius (mm) = 337.5/(diopter power)

30
Q

What is the corneal topography map that is the curvature relative to the optical axis? 1. Where on the cornea is this limited? 2

A
  1. axial maps or sagittal maps

2. peripheral cornea

31
Q

What is the corneal topography map that is the curvature measured via tangent to the normal and is the shape at a certain point? 1. What is this especially good for? 2

A
  1. tangential map or instantaneous map

2. peripheral corna and identifying pathology

32
Q

What is the corneal topography map that is the refractive power of the cornea? 1. What is this especially good for? 2

A
  1. refractive power map

2. pre and post refractive surgery

33
Q

What is the corneal topography map that is the difference in height from a reference sphere from reference point?

A

elevation map

34
Q

At what amount of gap between lens and cornea do bubbles form?

A

over 90 microns

35
Q

If there is inferior edge lift off for a Rose K lens, what should be done?

A

ACT to steepen PC in inferior

III. Advanced Contact Lenses (16 decks)

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