Fitting Irregular Corneas Flashcards
Forme Fruste Keratoconus
aka subclinical keratoconus
Cornea lacking abnormal findings on both SLE and cornea topography; fellow eye has clinical keratoconus
Where is the steepening of the cornea in Keratoconus
central or inferior central cornea
Where is the corneal thinning in PMD?
More inferior than KCN; near the limbus
CL fitting and corneal transplant can be more challenging
Keratoglobus
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
What does corneal ectasia lead to?
irregular astigmatism, central anterior scarring, and reduced vision
What 3 factors are thought to play a role in the onset, progression and stabilization of KCN?
genetics, environment and the individual’s endocrine system
environment= allergies, eye rubbing, etc
What is the most significant risk factor for KCN?
having a first-degree relative with KCN
What type of disorders are over-represented among patients with KCN?
connective tissue disorders
suggests underlying structural abnormalities
What 3 inflammatory factors have been shown to play a significant role in KCN even though it is considered a non-inflammatory condition?
proteolytic enzymes, cytokines, and free radicals
What was found in high levels in the tears of patients with KCN?
IL-6, TNF-alpha, MMP-9
eye rubbing has been shown to increase MMP-13, IL-6 and TNF-a
Levels of which vitamin were found to be significantly reduced in keratoconic patients?
Vitamin D
How does BMI play a factor in KCN?
adolescents that are overweight or obese had greatest prevelence and odds of having KCN
as BMI increases, so does KCN
Is the decrease in vision at disance or near?
both
also: distortion, ghosting, glare, diplopia
What might you see on retinoscopy?
scissoring reflex and increased astigmatism
What does Keratometry, Topography and OCT show in patients with KCN?
corneal steepening and disotortion
elevation map changes; posterior may occur first
Where is a Fleischer’s ring found?
deep epithelium; encircles the base of the cone
iron ring: can be complete or partial
In what layer can corneal thinning and scarring be seen under SLE?
stroma
Where is Vogt’s Striae?
deep stroma/ descemet’s membrane
What is this?
Munson’s sign
sign of advanced disease
What is this?
Rizzuti’s sign
found in advanced cases
cone shape of cornea causes iris light reflection to come to a point
What is this?
Oil droplet sign
Charleux sign
dark reflex in the area of the cone
What is this?
Hydrops
rupture of DM causing diffuse scarring
What are the stages of Keratoconus?
Generalization only
- <48 D
- 48-53 D
- 53-55 D
- > 55D
these are the same for both AK classification and Belin ABCD
What are the 4 parameters in the ABCD system?
A. Anterior Radius of Curvature
B. Posterior Radius of Curvature
C. Thinnest Pachymetry
D. Distance BCVA
How often is topography repeated for KCN patients?
~ every 6 months
especially in younger patients
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
Final D: linear regression analysis against a standard database of normal and KC corneas
What is the index of vertical asymmetry?
mean difference between superior and inferior corneal curvature
>0.28: abnormal
»0.32: pathological
What are the 3 surgical options for Keratoconus?
Penetrating keratoplasy; Intacs, Corneal crosslinking
Corneal GP or Scleral?
1. </= 200um difference:
2. 201-400um difference:
3. >/= 401um difference:
- corneal GP
- either
- Scleral
When fitting a keratoconic patient in SCL, what material is the best choice?
SiHy
thicker, can mask some astigmatism
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
What are some go-to SCL’s to try for a mild KC cornea?
Daily: MyDay Toric, BioTrue ONEday for astigmatism
Monthly: Proclear Toric
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
28% increase per diopter of increased curvature
Do we fit GP lenses slightly larger or smaller than HVID-2 for KC patients?
slightly smaller
usually 8-9.5mm OAD
Good fit goals for KC patients
- “feathery” 3-point touch to slight apical clearance
- No seal-off
- No large/ persistent air bubbles
- Wearable
What Dk do we order for KC patients wearing corneal GPs?
moderate to high
can consider Dk>100
avoids epithelial hypoxia and corneal erosion
Why would we fit a piggyback sytem for KCN?
- increase comfort, tolerance
- manage SPK
- manage very steep corneas
What material should the SCL be when fitting piggyback?
SiHy Daily disposable
allows increased oxygen
look for steeper sag values
What should the power of the SCL be when fitting piggyback?
low: +0.50--0.50
What percentage of the SCL manifests in the over-refraction?
20-30%
How do you calculate the amount of SCL power coming through?
over-refraction/SCL power used
NovaKone is an example of what type of CL?
specialty soft
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
How to increase edge lift of a scleral lens?
flatten PCs
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
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
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
What is the only manufacturer of hybrid lenses?
SynergEyes
Which hybrid lenses are for regular corneas?
come in both sphere and multifocal
Duette; iD
available in various BC
Which hybrids are available for irregular corneas?
ClearKone, UltraHealth
sphere powers only
multiple sag depth values
What parameter is used to change the fluorescein pattern?
central BC/ vault
What parameter of a hybrid lens is modified when there is an issue with centration or movement?
skirt radius
What do you do to the skirt radius if there is excessive movement and/ or decentration?
steepen skirt radius
How is the skirt radius changed if there is inadequate movement?
flatten skirt radius
Which hybrid lens absolutely needs fluorescein evaluation?
ultrahealth
can use regular fluorescein, skirt made of SiHy
goal: minimal apical clearance
Which hybrid lens has a skirt made of traditional hydrogel material?
can’t use NaFl with hydrogel
ClearKone
How much movement is ideal for hybrid lenses
0.50-1.00 mm
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
lens settles 50 microns with wear
What type of solutions can be used for hybrids?
SCL-approved solutions
OptiFree PureMoist, Biotrue, Clear Care
What are the FDA approved filling solutions for hybrids and sclerals?
- LacriPure
- ScleralFil
- VibrantVue
- Nutrifill
What are 3 filling solutions that are used ‘off-label’?
- PuriLens Plus
- AddiPak (NaCl 0.9% solution)
- Refresh PF artificial tears
How is the initial lens base curve calculated for Hybrid lenses?
mean K
steeper than flat K typically
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
How is the amount of vault controlled for scleral lenses?
sagittal depth
How big is a mini-scleral lens?
Up to 6 mm larger than HVID
How big is a large Scleral lens?
more than 6mm larger than HVID
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
suction develops secondary
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
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
What are 4 main uses of scleral lenses?
- Keratoconus
- PMD
- Post-surgical irregular astigmatism
- Ocular surface disease
OSD: dry eye, exposure keratitis, steven johnson syndrome, ocular cicatricial pemphigoid; graft versus host disease
What are 3 contraindications to scleral lenses?
- low endothelial cell density
- glaucoma
- overnight wear
may be able to work around a bleb if needed
Scleral lenses are primarily fit on ___________ ____________
sagittal depth
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)
this example is 1:1, so there is 300microns of clearance
What are the 7 steps to scleral lens design?
- Determine overall diameter
- Determine sagittal depth
- Assess central clearance
- Assess transition zone (limbal clearance)
- Assess landing zone
- Over-refract
- Choose Dk
How much does an average scleral lens settle?
100 microns
why we use 300 when calculating sag for irregular corneas and 200 for regular corneas
What is considered an excessive central vault?
> 500 microns
What is considered an inadequate central vault?
<100 microns
How much limbal clearance do we want for a scleral lens?
75-100 microns after settling
ok to have 100-200 microns upon insertion
Why are limbal stem cells so important?
crucial for corneal health; process new epithelial cells that are distributed over the entire cornea
What is typically wrong when a patient complains of discomfort/ lens awareness when wearing a scleral lens?
too much edge lift
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
What Dk is used for scleral lenses?
As high as possible
minimum 100; aim for >150
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)
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
What solutions can be used for scleral lenses?
GP solutions, plus peroxide solutions (ClearCare)
What instrument do we use to confirm central and limbal clearance?
Anterior Seg OCT
How do you fix corneal touch with scleral lenses?
Increase sagittal depth
How do you fix lens compression and seal off with scleral lenses?
may see limbal conjunctival hyperemia
flatten outer landing zone
How do you fix mid-day fogging/ reservoir debris?
reduce sag; flatten scleral landing zone
r/o and manage OSD
pt will need to remove, clean and refill lens
