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CL 3 Final > Fitting Irregular Corneas > Flashcards

Fitting Irregular Corneas Flashcards

1
Q

Forme Fruste Keratoconus

aka subclinical keratoconus

A

Cornea lacking abnormal findings on both SLE and cornea topography; fellow eye has clinical keratoconus

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2
Q

Where is the steepening of the cornea in Keratoconus

A

central or inferior central cornea

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3
Q

Where is the corneal thinning in PMD?

A

More inferior than KCN; near the limbus

CL fitting and corneal transplant can be more challenging

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4
Q

Keratoglobus

A

globular protrusion of the cornea and diffuse corneal thinning, most severe peripherally

congenital: Ehler-Danlos type VI; Leber’s and blue sclera syndrome

aquired: PMD, KCN; vernal keratoconjunctivitis, dysthyroid ophthalmopathy; chronic marginal bleph

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5
Q

What does corneal ectasia lead to?

A

irregular astigmatism, central anterior scarring, and reduced vision

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6
Q

What 3 factors are thought to play a role in the onset, progression and stabilization of KCN?

A

genetics, environment and the individual’s endocrine system

environment= allergies, eye rubbing, etc

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7
Q

What is the most significant risk factor for KCN?

A

having a first-degree relative with KCN

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8
Q

What type of disorders are over-represented among patients with KCN?

A

connective tissue disorders

suggests underlying structural abnormalities

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9
Q

What 3 inflammatory factors have been shown to play a significant role in KCN even though it is considered a non-inflammatory condition?

A

proteolytic enzymes, cytokines, and free radicals

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10
Q

What was found in high levels in the tears of patients with KCN?

A

IL-6, TNF-alpha, MMP-9

eye rubbing has been shown to increase MMP-13, IL-6 and TNF-a

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11
Q

Levels of which vitamin were found to be significantly reduced in keratoconic patients?

A

Vitamin D

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12
Q

How does BMI play a factor in KCN?

A

adolescents that are overweight or obese had greatest prevelence and odds of having KCN

as BMI increases, so does KCN

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13
Q

Is the decrease in vision at disance or near?

A

both

also: distortion, ghosting, glare, diplopia

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14
Q

What might you see on retinoscopy?

A

scissoring reflex and increased astigmatism

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15
Q

What does Keratometry, Topography and OCT show in patients with KCN?

A

corneal steepening and disotortion

elevation map changes; posterior may occur first

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16
Q

Where is a Fleischer’s ring found?

A

deep epithelium; encircles the base of the cone

iron ring: can be complete or partial

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17
Q

In what layer can corneal thinning and scarring be seen under SLE?

A

stroma

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18
Q

Where is Vogt’s Striae?

A

deep stroma/ descemet’s membrane

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19
Q

What is this?

A

Munson’s sign

sign of advanced disease

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20
Q

What is this?

A

Rizzuti’s sign

found in advanced cases

cone shape of cornea causes iris light reflection to come to a point

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21
Q

What is this?

A

Oil droplet sign

Charleux sign

dark reflex in the area of the cone

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22
Q

What is this?

A

Hydrops

rupture of DM causing diffuse scarring

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23
Q

What are the stages of Keratoconus?

Generalization only

A
  1. <48 D
  2. 48-53 D
  3. 53-55 D
  4. > 55D

these are the same for both AK classification and Belin ABCD

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24
Q

What are the 4 parameters in the ABCD system?

A

A. Anterior Radius of Curvature
B. Posterior Radius of Curvature
C. Thinnest Pachymetry
D. Distance BCVA

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25
Q

How often is topography repeated for KCN patients?

A

~ every 6 months

especially in younger patients

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26
Q

What are the 5 paramaters denoted in the Belin/Ambrosio display?

A
  • Df: changes in anterior elevation
  • Db: changes in posterior elevation
  • Dt: corneal thickness at the thinnest point
  • Da: thinnest pointdisplacement
  • Dp: pachymetric progression

Final D: linear regression analysis against a standard database of normal and KC corneas

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27
Q

What is the index of vertical asymmetry?

A

mean difference between superior and inferior corneal curvature

>0.28: abnormal
»0.32: pathological

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28
Q

What are the 3 surgical options for Keratoconus?

A

Penetrating keratoplasy; Intacs, Corneal crosslinking

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29
Q

Corneal GP or Scleral?
1. </= 200um difference:
2. 201-400um difference:
3. >/= 401um difference:

A
  1. corneal GP
  2. either
  3. Scleral
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30
Q

When fitting a keratoconic patient in SCL, what material is the best choice?

A

SiHy

thicker, can mask some astigmatism

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31
Q

What might be a challenge when fitting toric SCL on a keratoconic eye?

A

may be hard to stabilize on the cornea if irregular

especially inferior steepening

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32
Q

What are some go-to SCL’s to try for a mild KC cornea?

A

Daily: MyDay Toric, BioTrue ONEday for astigmatism
Monthly: Proclear Toric

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33
Q

According to the CLEK study, what increases the risk of prevalent corneal curvature?

A

Steeper corneal curvature

wearing GPs is associated w/ increased risk of scarring; occurs w/o cl

28% increase per diopter of increased curvature

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34
Q

Do we fit GP lenses slightly larger or smaller than HVID-2 for KC patients?

A

slightly smaller

usually 8-9.5mm OAD

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35
Q

Good fit goals for KC patients

A
  • “feathery” 3-point touch to slight apical clearance
  • No seal-off
  • No large/ persistent air bubbles
  • Wearable
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36
Q

What Dk do we order for KC patients wearing corneal GPs?

A

moderate to high

can consider Dk>100

avoids epithelial hypoxia and corneal erosion

37
Q

Why would we fit a piggyback sytem for KCN?

A
  • increase comfort, tolerance
  • manage SPK
  • manage very steep corneas
38
Q

What material should the SCL be when fitting piggyback?

A

SiHy Daily disposable

allows increased oxygen

look for steeper sag values

39
Q

What should the power of the SCL be when fitting piggyback?

A

low: +0.50--0.50

40
Q

What percentage of the SCL manifests in the over-refraction?

A

20-30%

41
Q

How do you calculate the amount of SCL power coming through?

A

over-refraction/SCL power used

42
Q

NovaKone is an example of what type of CL?

A

specialty soft

43
Q

What is an alternative to steepening the base curve when a lens is decentered superiorly and has unequal edge lift?

A

increase overall diameter

do not need SAM-FAP

44
Q

How to increase edge lift of a scleral lens?

A

flatten PCs

45
Q

When is a hybrid lens a good choice for a patient with irregular corneas secondary to keratoconus or post-surgery?

A

non-adapters to GP lenses; unable to master insertion/ removal of scleral lenses

46
Q

When is a hybrid lens a good choice for patients with mild corneal irregularity?

A

specatacle vision is unacceptable; they desire better vision than what traditional spherical or astigmatic soft lenses can provide

47
Q

When is a hybrid lens a good choice for a patient with presbyopia?

A

up to 6.00 D of corneal astigmatism; soft MF-toric patients or soft toric-monovision patients who want better vision and/ or binocular vision

48
Q

What is the only manufacturer of hybrid lenses?

A

SynergEyes

49
Q

Which hybrid lenses are for regular corneas?

come in both sphere and multifocal

A

Duette; iD

available in various BC

50
Q

Which hybrids are available for irregular corneas?

A

ClearKone, UltraHealth

sphere powers only

multiple sag depth values

51
Q

What parameter is used to change the fluorescein pattern?

A

central BC/ vault

52
Q

What parameter of a hybrid lens is modified when there is an issue with centration or movement?

A

skirt radius

53
Q

What do you do to the skirt radius if there is excessive movement and/ or decentration?

A

steepen skirt radius

54
Q

How is the skirt radius changed if there is inadequate movement?

A

flatten skirt radius

55
Q

Which hybrid lens absolutely needs fluorescein evaluation?

A

ultrahealth

can use regular fluorescein, skirt made of SiHy

goal: minimal apical clearance

56
Q

Which hybrid lens has a skirt made of traditional hydrogel material?

can’t use NaFl with hydrogel

A

ClearKone

57
Q

How much movement is ideal for hybrid lenses

A

0.50-1.00 mm

58
Q

How much clearance should there be at the initial fit of a hybrid lens?

A

100 microns

lens is 200 microns thick, clearance should be 1/2 lens thickness

lens settles 50 microns with wear

59
Q

What type of solutions can be used for hybrids?

A

SCL-approved solutions

OptiFree PureMoist, Biotrue, Clear Care

60
Q

What are the FDA approved filling solutions for hybrids and sclerals?

A
  • LacriPure
  • ScleralFil
  • VibrantVue
  • Nutrifill
61
Q

What are 3 filling solutions that are used ‘off-label’?

A
  • PuriLens Plus
  • AddiPak (NaCl 0.9% solution)
  • Refresh PF artificial tears
62
Q

How is the initial lens base curve calculated for Hybrid lenses?

A

mean K

steeper than flat K typically

63
Q

What is lens power based on for Hybrid lenses?

A

the spherical component of spectacle Rx in (-) cyl

adjusted based on tear lens; SAM/FAP; and vertex

64
Q

How is the amount of vault controlled for scleral lenses?

A

sagittal depth

65
Q

How big is a mini-scleral lens?

A

Up to 6 mm larger than HVID

66
Q

How big is a large Scleral lens?

A

more than 6mm larger than HVID

67
Q

What are the two forces that hold the scleral lens in place?

the same forces that allow them to hold a fluid reservoir

A

Surface tension and suction (sub-atmospheric pressure)

surface tension allows the scleral lens to stick to the eye surface

suction develops secondary

68
Q

Why do scleral lenses put stress on the corneal endothelium?

A

no tear exchange like corneal GPs; sclerals are dependent on oxygen transmission through the lens only

69
Q

What is a possible consequence of compressed episcleral veins (and the underlying Schlemm’s canal) when wearing a scleral lens?

A

Decreased outflow and increased IOP

70
Q

What are 4 main uses of scleral lenses?

A
  • Keratoconus
  • PMD
  • Post-surgical irregular astigmatism
  • Ocular surface disease

OSD: dry eye, exposure keratitis, steven johnson syndrome, ocular cicatricial pemphigoid; graft versus host disease

71
Q

What are 3 contraindications to scleral lenses?

A
  • low endothelial cell density
  • glaucoma
  • overnight wear

may be able to work around a bleb if needed

72
Q

Scleral lenses are primarily fit on ___________ ____________

A

sagittal depth

73
Q

Label the picture

A

a. front surface of lens
b. center thickness
c. clearance
d. corneal thickness

to find vault: comparing central thickness (b) to clearance (c)

this example is 1:1, so there is 300microns of clearance

74
Q

What are the 7 steps to scleral lens design?

A
  1. Determine overall diameter
  2. Determine sagittal depth
  3. Assess central clearance
  4. Assess transition zone (limbal clearance)
  5. Assess landing zone
  6. Over-refract
  7. Choose Dk
75
Q

How much does an average scleral lens settle?

A

100 microns

why we use 300 when calculating sag for irregular corneas and 200 for regular corneas

76
Q

What is considered an excessive central vault?

A

> 500 microns

77
Q

What is considered an inadequate central vault?

A

<100 microns

78
Q

How much limbal clearance do we want for a scleral lens?

A

75-100 microns after settling

ok to have 100-200 microns upon insertion

79
Q

Why are limbal stem cells so important?

A

crucial for corneal health; process new epithelial cells that are distributed over the entire cornea

80
Q

What is typically wrong when a patient complains of discomfort/ lens awareness when wearing a scleral lens?

A

too much edge lift

81
Q

When do you add residual cyl to the front surface of a scleral lens?

A

when it is >0.75 D

similar to front toric GP

82
Q

What Dk is used for scleral lenses?

A

As high as possible

minimum 100; aim for >150

83
Q

With scleral lenses, what does oxygen transmission depend on?

A
  • thickness of scleral lens
  • Dk of lens material chosen
  • Thickness of lens tear layer
  • Dk of tears (80)
84
Q

Considering the following equation, what is the minimum criterial for both the central cornea and the limbal area to reduce hypoxia-induced corneal swelling?

A

Central cornea: 24
Limbal area: 35

84
Q

What solutions can be used for scleral lenses?

A

GP solutions, plus peroxide solutions (ClearCare)

84
Q

What instrument do we use to confirm central and limbal clearance?

A

Anterior Seg OCT

85
Q

How do you fix corneal touch with scleral lenses?

A

Increase sagittal depth

86
Q

How do you fix lens compression and seal off with scleral lenses?

may see limbal conjunctival hyperemia

A

flatten outer landing zone

87
Q

How do you fix mid-day fogging/ reservoir debris?

A

reduce sag; flatten scleral landing zone

r/o and manage OSD

pt will need to remove, clean and refill lens

CL 3 Final (8 decks)

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