Keratoconus and Related Non-Inflammatory Thinning Disorders

Timothy T. McMahon, OD

Department of Ophthalmology and Visual Sciences

University of Illinois at Chicago

Non-Inflammatory Thinning Disorders

Keratoconus Pellucid Marginal Degeneration Posterior Keratoconus Keratoglobus Terrien’s Marginal Degeneration Senile Marginal Furrowing

Keratoconus

Non-inflammatory Central and Paracentral Thinning Steepening, Principally Central and Inferior M>F, (60% M) Prevalence - Approx. 230/100,000 96% Bilateral Types: Nipple, Oval, Globoid

Demographics: Prevalence

Range: 4 to 600 per 100,000 Most Common: 230/100,000

Demographics: Gender

% Female Range 22-56% Mean % Female 38.7% 6255 Patients (2423 Females) 10 Studies M:F Ratio 1.58:1

Demographics: Bilaterality

Prior to Topography: 85.% Bilateral After Topography: 96% Bilateral

Demographics: Race

No Racial Predilection

Demographics: Age

Age <20 20-29 30-39 40-49 50-59 60-69 >70

Percent of Sample

4

26

33

25

8

3

1

Demographics: Age

Age at Diagnosis <10 10-19 20-29 30-39 40-49 50-59 >60

Percent of Sample

0.2

20.6

44.2

24.9

7.9

1.6

0.6

Corneal Thinning

Fleischer Ring

Corneal Nerve Fibers More Visible

Munson’s Sign

Vogt Striae

Corneal Hydrops

Corneal Hydrops

Hurricane (Whorl) Keratopathy

Ophthalmoscopy Reflex

Ophthalmoscopy Reflex

Slit Lamp FindingsEye

___________

Vogt’sStriae___________

Fleischer’sRing___________

CornealScarring___________

Neither 48% 36% 57%

One Eye 23% 21% 23%

Both Eyes 29% 43% 20%

Keratometry

Slit Lamp Findings by K’sSeverity Rank: CLEK Study

DiseaseSeverity___________

Vogt Striae

___________

Fleischer’sRing___________

CornealScarring___________

Mild(<45 D)

21% 33.8% 9%

Moderate(45-52 D)

40% 53% 22%

Advanced(>52 D)

60% 67% 67%

Pathology

Breaks in Bowman’s Membrane

Loss of Stromal Substance

Anterior Stromal Scarring

Tears in Descemet’s Membrane (Hydrops)

Pathology

Reduced Protein Content Reduced Protein and Collagen Production

When Grown in Culture in Some KCN Corneas but not all

Pathology

Elevated Lysosomal Enzymes in the Epithelium and Conjunctiva (but not the Skin)– acid phosphatase– acid esterase

Elevated Lysome Enzymes in the Corneal Epithelium– acid lipase

Pathology

Reduced Levels of Protease Inhibitors in the Epithelium and Stroma– alpha-1-protease inhibitor– alpha-2-macroglobulin

Pathology

Elevated levels of Inflammatory Products in Cultured KCN Corneas– 4X increase IL-1 receptors– 10X increase in Cyclooxygenase Vmax

(kinetics of cytokine system)– 10X increase in PGE2 production– increase in TGF beta

Pathology

Evidence supports the hypothesis that there is an acceleration in cellular degradation processes associated with an increase in degratory enzymes as a result of the suppression of inhibitory enzymes in the corneal epithelium, the conjunctival epithelium, and maybe the stroma.

Pathology

There is evidence of the inflammatory system being involved

It is likely that this is a secondary (response) mechanism

Genetic Disorder Suggested by:

Familial occurrence (13.5% in CLEK) 15-67X greater in 1st degree relatives than in

the general population Twin Studies Bilaterality

Linkage Studies

16q 22.3 – q23.1 Finland

20q 12 Tasmania

21 Utah

20 pII-qII Canada

3p14-q13 Italy

6p 25 Canada

Keratoconus: Complex Genetic Disorder

Multiple genes may come into play Other modifier genes may be involved

Interaction between genetic and non-genetic factors

Treatment Options

Spectacles Soft Lenses Rigid Corneal Lenses Piggy Back Lenses Scleral Lenses Penetrating Keratoplasty

Vision by Correction Type

VA_______________

CL________________

GLASSES________________

20/20 or + 32% 14%

20/21-20/40 56% 44%

20/41-20/60 8% 16%

<20/60 4% 26%

Keratoconus - RGP Corneal Lenses

Fitting Philosophies Fitting Method(s)

Keratoconus - Fitting Philosophies

Flat, Reshape the Cornea Flat, Three Point Touch Steep, Apical Clearance

Notice!

A “bad looking fit” is not a reason to change a lens

When To Change a Lens (General)

To Improve Vision To Improve Comfort To Reduce Physical Insult To Keep the Lens on the Cornea

When To Change a Lens (Specific)

Change in Power > .50 D That Improves VA 1 Line or More

Increasing Discomfort Increasing Lens Dislodgement (>3X/wk) Decreasing Wearing Time That is Fit Related Chronic Epithelial Whorl Staining Development of Subepithelial Nodule

Monitor

Central VA Hx of VA at Night Hx of Light Sensitivity Lens Behavior Epithelial Staining

Contact Lens Failure

43% Poor Visual Acuity 32% Contact Lens Intolerance 12% Peripheral Thinning

Reasons For Surgery

Visual Acuity <20/40, Loss of Function Lens Intolerance Can’t Keep a Lens on the Eye Frequent Corneal Abrasions With Severe

Disease Peripheral Corneal Thinning

Clinical Pearls

Glasses should be considered Use a large RGP for 1st timers with mild

steepening You can’t follow standard fitting protocols Evaluate edge clearance as carefully as you

do the central fitting relationship

Clinical Pearls

Move to a smaller design when you can (8.2-8.6 mm)

You’ll end up fitting much flatter than K as the disease progresses

If it isn’t broken, don’t fix it!

Pellucid Marginal Degeneration

Very uncommon Generally bilateral Onset: Age 10-30

years Inferior arcuate

thinning– width 1-2 mm

– length 4-8 mm

– 1-2 mm from limbus

Pellucid Marginal Degeneration

Steepening above the thinned area

Central A/R astigmatism

Inferior W/R astigmatism

Slowly progressive “Inferior keratoconus”

Pellucid Marginal Degeneration

Pellucid Marginal Degeneration

Pellucid Marginal Degeneration

Spectacles Rigid contact lenses Crescentic lamellar

graft Large central

penetrating graft Combined procedure

Posterior Keratoconus

Rare Normal anterior

curvature (?) Steep posterior

curvature– diffuse or focal

Usually unilateral

Posterior Keratoconus

Posterior scarring Synechiae (sometimes) Present at birth Mesynchemal dysgenesis disorder

Posterior KeratoconusAssociated Conditions

Choroidal and retinal sclerosis Retinal coloboma Optic nerve hypoplasia Lens defects Posterior polymorphous dystrophy Ptosis

Keratoglobus

Rare Bilateral Clear, thin, limbus to

limbus Thinning is greatest

near or at the limbus 1/3 to 1/5 normal

thickness Nonprogressive

Keratoglobus

Present at birth High risk of

perforation (70%) May have Hydrops No association with

congenital glaucoma or megalocornea

Contact lenses are contraindicated

Terrien’s Marginal Degeneration

Any age/mostly middle-older adults

Bilateral (>80%), asymmetric

Slowly progressive Generally painless, but

may have painful episodes

Terrien’s Marginal Degeneration

Increase in cylinder, usually A/R

Flat meridian points to thinned area

20% have oblique pterygium

Senile Marginal Furrowing

Shallow peripheral thinning

Next to limbus Slowly progressive No epithelial defects No pain May have topographic

changes

Senile Marginal Furrowing

No vessels Sloping edges, no

guttering

THANK YOU!

Keratoconus GP Fitting Methods

Keratoconus - Flat, Reshape

Least Common Method Bronstein et al Sphericize the Cornea “Retard Progression” by Tamponade Generally Fit Large and Quite Flat

Flat, Reshape

Keratoconus - Three Point Touch

Most Popular Method No Intention to Change Shape Apical Touch or Bearing Mid-peripheral Bearing Peripheral Edge Clearance

Three-Point Touch

Flat 3-Point Touch

Keratoconus - Apical Clearance

Vaults Corneal Apex Mid-peripheral Bearing/Support Technically, the Most Difficult Method ? Reduces the Likelihood of Scars Forming

Apical Clearance

Keratoconus - SeveritySeverity Rank: McMahon

Average Keratometry Value Mild: 43.00-51.75 Moderate: 52.00-57.00 Severe: 57.25 +

Flat Fitting Method

Three-Point Touch (Flat Bias) Three-Point Touch (Steep Bias)

Mild Cone (Virgin)Flat Bias

Large Diameter (9.4-9.7 mm) Lid Supported Fit on K to 1.00D Flat Tricurve Design Spherical Base Curve

Mild Cone (Veteran)Flat Bias

Moderate Diameter (8.2-8.6 mm) Non-lid Supported Fit on K Tricurve Design Spherical Base Curve

Moderate ConeFlat Bias

Moderate Diameter (8.2-8.6 mm) Non-lid Supported Bispheric Base Design One Peripheral Curve, Flat Fit 1.00 D Flat if Average K = 52.00-54.00 Fit 2.00 D Flat if Average K = 54.25-57.00

Severe Cone Flat Bias

Try Moderate Diameter First (8.2-8.6 mm) Fit 3-4 Diopters Flat If Unstable, Large Diameter (9.4-9.7 mm) Fit 5-6 Diopters Flat Bispheric Design One, Flat Peripheral Curve Non-lid Supported

Mild Cone (Virgin)Steep Bias

Large Diameter (9.4-9.7 mm) Lid Supported Fit on K to 0.50D Steep Tricurve Design Spherical Base Curve

Mild Cone (Veteran)Steep Bias

Moderate Diameter (8.2-8.6 mm) Non-lid Supported Fit .75 D Steeper than K Tricurve Design Spherical Base Curve

Moderate ConeSteep Bias

Moderate Diameter (8.2-8.6 mm) Non-lid Supported Bispheric Base Design One Peripheral Curve, Flat Fit On K if Average K = 52.00-54.00 Fit 1.00 D Flat if Average K = 54.25-57.00

Severe Cone Steep Bias

Try Moderate Diameter First (8.2-8.6 mm) Fit 1-2 Diopters Flat If Unstable, Large Diameter (9.4-9.7 mm) Fit 3-4 Diopters Flat Bispheric Design One, Flat Peripheral Curve Non-lid Supported

Apical Clearance Fitting

Diameter 7.5 to 8.5 mm Use Steep K Find First Definite Apical Clearance Base

Curve (Fluorescein) Two Peripheral Curves (First is Wide)