keratoconus and specialty contact lens fitting of irregular corneas

Marc L. Braithwaite, OD

Vision Care of Maine

Keratoconus

What have the years taught us?

Keratoconus Characteristics Non-inflammatory. Central or para-central corneal thinning. Corneal steepening or protrusion. Increased astigmatism and possibly

myopia. Loss of best spectacle corrected visual

acuity. Corneal striae and scarring. Corneal hydrops (inflammatory).

Pathology of Keratoconus

Loss of Bowman’s Layer.

Stromal Thinning.

Apoptosis.

Increased Enzyme Activity.

Enlarged Prominent Corneal Nerves.

Causes of Keratoconus

Heredity vs. Mechanical

Cellular

Tissue

Genetic

Heredity vs. Mechanical

Does eye rubbing cause Keratoconus? 2 out of 250 doctors feel that rubbing is

a cause. KC patients do rub their eyes more often

than those without KC. What is it that makes KC patients rub

their eyes?

Cellular Changes

Keratoconus cells are hypersensative. Increased enzyme activity, lack of

enzyme inhibitors. Matrix substrate instability in response

to environmental stress factors. mtDNA damage and exaggerated

oxidative response causing cellular damage.

Tissue Changes

Loss of Bowman’s layer.

Lamellar slippage.

Lack “anchoring” lamellar fibrils.

Apoptosis of the stroma causing anterior

thinning.

Genetics

Autosomal dominant w/variable penetrance.

SOD1, an antioxidant enzyme, is abnormal in some KC corneas.

No single gene responsible. 10 different chromosomes have been

associated with KC. Most likely multiple genes involved.

Additional Information Male to Female Ratio = 3:1 Approximately 20% result in PKP. 90% are diagnosed by optometrists. Mean age of diagnosis is 22.88 years. Visual outcome with RGP is better than

PKP. More prevalent in certain ethnic groups (4x

higher in Asians from Indian sub-continent regions than White Europeans).

Progression and Prognosis Age is a big factor. The younger the diagnosis, the poorer

the prognosis. Less likely to progress to the point of a

transplant if diagnosed in the 30’s. 20% of Keratoconus patients result in

corneal transplants. 35 to 45% of all transplants are due to

Keratoconus.

Possible Aggravating Factors UV exposure.

Allergies.

Vigorous eye rubbing.

Poorly fitting contact lenses.

Inflammation.

Types of Keratoconus

Nipple/Oval cone - central or mildly para-central localized thinning and steepening.

Keratoglobus - Large generalized thinning and steepening.

PMD (pellucid marginal degeneration) – peripheral thinning and steepening.

Keratoconus Fruste – Less progressive and less manipulative.

Nipple/Oval Cone

Central Steepening Steepest form

Keratoglobus

Wider – 75 to 90% of cornea. Not as steep.

Pellucid Marginal Degeneration Peripheral Thinning

Orbscan Analysis

How to Treat Keratoconus Spectacles Contacts

Soft StandardSoft CustomRGP StandardRGP CustomHybrid

SurgeryIntacsPenetrating Keratoplasty

Riboflavin/UV treatment

When to Intervene?

Best Spectacle/Soft CL Acuity 20/30 or better?Good tolerance of acuity.Corneal health is not compromised.“If it aint broke, don’t fix it.”

Best Spectacle/Soft CL Acuity worse than 20/30?Specialized contact lenses.My opinion, use RGP lenses.

Which RGP Design?

Early KeratoconusStandard RGPKC RGP

Mid-stage KeratoconusKC RGPCustom KC RGP

Advanced KeratoconusCustom KC RGPIntra-limbal or Scleral RGP

My “GO TO” Lens – Rose K Developed by Dr. Paul Rose. Designed to fit the irregular cornea. “Very forgiving lens” Multiple designs to fit all shapes of

corneas and corneal conditions. Blanchard is very good to work with and

has staff to assist with very difficult cases.

Nipple/Oval Cone Fitting

Most common form of KC. Early stages - simple RGP or KC RGP Later stages – KC RGP usually small

and steep. The steeper the cone, the smaller the

lens diameter.

Rose K2

Rose K vs. Rose K2 72% of patients notice an increase in

acuity with aspheric, aberration control. Lens to be centered on the cone. Reduce excessive movement (1 to

2mm).

Fitting the Rose K2

Too high – tighten edge lift

reduce OAD

steepen base curve

Too low – increase edge lift

increase OAD

flatten base curve

Fitting the Rose K2

Centrally fitting the

lens on a nipple

cone better insures

optimal acuity and

comfort.

Rose K2IC

IC stands for irregular cornea Larger diameter Larger optic zone Aspheric for aberration control Reverse geometry design

PMD

Keratoglobus

LASIK induced ectasia

Corneal transplants

Corneal Dystrophies

Traumatic Corneas with Scars

Post RK

Irregular Astigmatism or Corneal Warpage

What is That?

Asymmetric Corneal Technology ACT.

ACT – Continued…

Using ACT ( Asymmetric Corneal Technology)

• 3 standard grades available • Option also to specify degree of tuck in 0.1 steps from 0.4 to 1.5mm

Grade 1 ( 0.7mm steeper)

Grade 2 (1.0mm steeper)

Grade 3 (1.3mm steeper)

Fitting with ACT

NO ACT WITH ACT

ACT - Improved comfort , lens stability and vision

Fitting with ACT

Toric Peripheral Curves

Fitting Pearls Tendency to tighten after initial fitting. Light central touch will increase acuity. Avoid central staining. Movement is necessary but slight

movement is usually sufficient. Pay attention to tear flow beneath lens. The steeper the lens, the smaller OAD and

less movement. Don’t change too many parameters at

once.

Penetrating KeratoplastyWhen to refer?

Acuity is 20/50 or worse. Patient intolerance to visual decrease. Scars within the visual axis. Multiple episodes of Hydrops. Contact lens intolerance. Unable to get adequate/healthy CL fit. Consider OD to OD referral. Give reasonable expectations.

Post PKP Management

How soon can you fit with lens? Why are the curvatures so strange? Do you have to wait for all sutures to be

removed? Corrective options.

SpectaclesRGP contact lenses.LASIK

Rose K2 Post Graft

PKP Topography

Rose K2 Post Graft

Much more difficult to fit than KC.

Patients are less tolerable to CL.

Eyes are more dry.

Ill-fitting contact lenses can lead to graft

rejection.

Lens design is crucial to success.

K2PG Fitting Pearls

Don’t be intimidated! Watch tear flow! Also good lens for ectasia patients. Stay with your fitting basics

Fit base curves.Adjust diameter.Adjust peripheral curves.Use ACT or Toric PC if needed.

Post Graft – Too Steep

Post Graft – Too Flat

Post Graft – Good Fit

Watch Vasculature

The Difficult Ones

Nothing is comfortable.

Acuity isn’t improving..

Eyes are too dry. (Sjogren’s Syndrome)

Cornea is too irregular for any lens to fit

properly or in a healthy manner.

What Do You Do?

Mini-Scleral Design - MSD Large RGP Vaults the cornea, rests on the sclera. Creates a fluid filled environment. Can be used to treat any corneal

condition. Can be used to treat other anterior

segment conditions.

MSD - Advantages

Very Stable lens.

Fluid filled environment.

Improved comfort.

Good visual acuity.

Mini-Scleral Design

MSD – Fitting Pearls

Central Feather-touch.

Intra-limbal adjustment.

With or without

fenestration or

fenestrations.

Watch edge for

tightening.

Practice Management Issues Setting Fees. Bill for services performed. Insurances and fee collection. Appropriate diagnostic and treatment

equipment.Topography/corneal mapping.Pachymetry.Fitting sets.

Refractive Surgery Specific Moderate – Large Diameter

(10.5 mm Standard Diameter, 9.5 mm to 12.0 mm).

Reverse Geometry Transition. Post Surgical Central BC.

Curves• Paracentral Fitting Curves.

• Asymmetric Corneal Technology (ACT).

Thank You!