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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
How often is topography repeated for KCN patients?
~ every 6 months | especially in younger patients
26
What are the 5 paramaters denoted in the Belin/Ambrosio display?
* Df: changes in anterior elevation * Db: changes in posterior elevation * Dt: corneal thickness at the thinnest point * Da: thinnest pointdisplacement * Dp: pachymetric progression ## Footnote Final D: linear regression analysis against a standard database of normal and KC corneas
27
What is the index of vertical asymmetry?
mean difference between superior and inferior corneal curvature | >0.28: abnormal >>0.32: pathological
28
What are the 3 surgical options for Keratoconus?
Penetrating keratoplasy; Intacs, Corneal crosslinking
29
Corneal GP or Scleral? 1. /= 401um difference:
1. corneal GP 2. either 3. Scleral
30
When fitting a keratoconic patient in SCL, what material is the best choice?
SiHy | thicker, can mask some astigmatism
31
What might be a challenge when fitting toric SCL on a keratoconic eye?
may be hard to stabilize on the cornea if irregular | especially inferior steepening
32
What are some go-to SCL's to try for a mild KC cornea?
Daily: MyDay Toric, BioTrue ONEday for astigmatism Monthly: Proclear Toric
33
According to the CLEK study, what increases the risk of prevalent corneal curvature?
Steeper corneal curvature | wearing GPs is associated w/ increased risk of scarring; occurs w/o cl ## Footnote 28% increase per diopter of increased curvature
34
Do we fit GP lenses slightly larger or smaller than HVID-2 for KC patients?
slightly smaller | usually 8-9.5mm OAD
35
Good fit goals for KC patients
* "feathery" 3-point touch to slight apical clearance * No seal-off * No large/ persistent air bubbles * Wearable
36
What Dk do we order for KC patients wearing corneal GPs?
moderate to high | can consider Dk>100 ## Footnote avoids epithelial hypoxia and corneal erosion
37
Why would we fit a piggyback sytem for KCN?
* increase comfort, tolerance * manage SPK * manage very steep corneas
38
What material should the SCL be when fitting piggyback?
SiHy Daily disposable | allows increased oxygen ## Footnote look for steeper sag values
39
What should the power of the SCL be when fitting piggyback?
low: +0.50--0.50
40
What percentage of the SCL manifests in the over-refraction?
20-30%
41
How do you calculate the amount of SCL power coming through?
over-refraction/SCL power used
42
NovaKone is an example of what type of CL?
specialty soft
43
What is an alternative to steepening the base curve when a lens is decentered superiorly and has unequal edge lift?
increase overall diameter | do not need SAM-FAP
44
How to increase edge lift of a scleral lens?
flatten PCs
45
When is a hybrid lens a good choice for a patient with irregular corneas secondary to keratoconus or post-surgery?
non-adapters to GP lenses; unable to master insertion/ removal of scleral lenses
46
When is a hybrid lens a good choice for patients with mild corneal irregularity?
specatacle vision is unacceptable; they desire better vision than what traditional spherical or astigmatic soft lenses can provide
47
When is a hybrid lens a good choice for a patient with presbyopia?
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
What is the only manufacturer of hybrid lenses?
SynergEyes
49
Which hybrid lenses are for regular corneas? | come in both sphere and multifocal
Duette; iD | available in various BC
50
Which hybrids are available for irregular corneas?
ClearKone, UltraHealth | sphere powers only ## Footnote multiple sag depth values
51
What parameter is used to change the fluorescein pattern?
central BC/ vault
52
What parameter of a hybrid lens is modified when there is an issue with centration or movement?
skirt radius
53
What do you do to the skirt radius if there is excessive movement and/ or decentration?
steepen skirt radius
54
How is the skirt radius changed if there is inadequate movement?
flatten skirt radius
55
Which hybrid lens absolutely needs fluorescein evaluation?
ultrahealth | can use regular fluorescein, skirt made of SiHy ## Footnote goal: minimal apical clearance
56
Which hybrid lens has a skirt made of traditional hydrogel material? | can't use NaFl with hydrogel
ClearKone
57
How much movement is ideal for hybrid lenses
0.50-1.00 mm
58
How much clearance should there be at the initial fit of a hybrid lens?
100 microns | lens is 200 microns thick, clearance should be 1/2 lens thickness ## Footnote lens settles 50 microns with wear
59
What type of solutions can be used for hybrids?
SCL-approved solutions | OptiFree PureMoist, Biotrue, Clear Care
60
What are the FDA approved filling solutions for hybrids and sclerals?
* LacriPure * ScleralFil * VibrantVue * Nutrifill
61
What are 3 filling solutions that are used 'off-label'?
* PuriLens Plus * AddiPak (NaCl 0.9% solution) * Refresh PF artificial tears
62
How is the initial lens base curve calculated for Hybrid lenses?
mean K | steeper than flat K typically
63
What is lens power based on for Hybrid lenses?
the spherical component of spectacle Rx in (-) cyl | adjusted based on tear lens; SAM/FAP; and vertex
64
How is the amount of vault controlled for scleral lenses?
sagittal depth
65
How big is a mini-scleral lens?
Up to 6 mm larger than HVID
66
How big is a large Scleral lens?
more than 6mm larger than HVID
67
What are the two forces that hold the scleral lens in place? | the same forces that allow them to hold a fluid reservoir
Surface tension and suction (sub-atmospheric pressure) | surface tension allows the scleral lens to stick to the eye surface ## Footnote suction develops secondary
68
Why do scleral lenses put stress on the corneal endothelium?
no tear exchange like corneal GPs; sclerals are dependent on oxygen transmission through the lens only
69
What is a possible consequence of compressed episcleral veins (and the underlying Schlemm's canal) when wearing a scleral lens?
Decreased outflow and increased IOP
70
What are 4 main uses of scleral lenses?
* Keratoconus * PMD * Post-surgical irregular astigmatism * Ocular surface disease ## Footnote OSD: dry eye, exposure keratitis, steven johnson syndrome, ocular cicatricial pemphigoid; graft versus host disease
71
What are 3 contraindications to scleral lenses?
* low endothelial cell density * glaucoma * overnight wear | may be able to work around a bleb if needed
72
Scleral lenses are primarily fit on ___________ ____________
sagittal depth
73
Label the picture
a. front surface of lens b. center thickness c. clearance d. corneal thickness | to find vault: comparing central thickness (b) to clearance (c) ## Footnote this example is 1:1, so there is 300microns of clearance
74
What are the 7 steps to scleral lens design?
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
How much does an average scleral lens settle?
100 microns ## Footnote why we use 300 when calculating sag for irregular corneas and 200 for regular corneas
76
What is considered an excessive central vault?
>500 microns
77
What is considered an inadequate central vault?
<100 microns
78
How much limbal clearance do we want for a scleral lens?
75-100 microns after settling | ok to have 100-200 microns upon insertion
79
Why are limbal stem cells so important?
crucial for corneal health; process new epithelial cells that are distributed over the entire cornea
80
What is typically wrong when a patient complains of discomfort/ lens awareness when wearing a scleral lens?
too much edge lift
81
When do you add residual cyl to the front surface of a scleral lens?
when it is >0.75 D | similar to front toric GP
82
What Dk is used for scleral lenses?
As high as possible | minimum 100; aim for >150
83
With scleral lenses, what does oxygen transmission depend on?
* thickness of scleral lens * Dk of lens material chosen * Thickness of lens tear layer * Dk of tears (80)
84
Considering the following equation, what is the minimum criterial for both the central cornea and the limbal area to reduce hypoxia-induced corneal swelling?
Central cornea: 24 Limbal area: 35
84
What solutions can be used for scleral lenses?
GP solutions, plus peroxide solutions (ClearCare)
84
What instrument do we use to confirm central and limbal clearance?
Anterior Seg OCT
85
How do you fix corneal touch with scleral lenses?
Increase sagittal depth
86
How do you fix lens compression and seal off with scleral lenses? | may see limbal conjunctival hyperemia
flatten outer landing zone
87
How do you fix mid-day fogging/ reservoir debris?
reduce sag; flatten scleral landing zone | r/o and manage OSD ## Footnote pt will need to remove, clean and refill lens

CL 3 Final (8 decks)

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