Keratoconus Update and RGP Fitting 2013 KL

8/12/2019 Keratoconus Update and RGP Fitting 2013 KL

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(c) Simon Lam 2013 1

Keratoconus UpdatesDiagnosis and Specialty Lenses Fitting

ByMr Simon Lam

PD in Opt (HKPU),BSc in Opt (USA), MBA (Hull), DACE (WDA)

Head Optometrist, Optic Point Pte Ltd

Visiting Lecturer, Republic Polytechnic, Singapore

Keratoconus

What have we learnt from the past?


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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 Bowmans Layer.

Stromal Thinning.

Apoptosis.

Increased Enzyme Activity.

Enlarged Prominent Corneal Nerves.


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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?


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Cellular Changes

Keratoconus cells are hypersensitive.

Increased enzyme activity, lack of enzyme

inhibitors.

Matrix substrate instability in response to

environmental stress factors.

mtDNA damage and exaggerated oxidativeresponse causing cellular damage.

Tissue Changes

Loss of Bowmans layer.

Lamellar slippage.

Lack anchoring lamellar fibrils.

Apoptosis of the stroma causing anterior

thinning.


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Progression and PrognosisAge is a big factor.

The younger the diagnosis, the poorer theprognosis.

Less likely to progress to the point of atransplant if diagnosed in the 30s.

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.


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Hallmarks of Keratoconus A decline in visual acuity (6/9 or below).

A distorted retinoscopy reflex.

Distortion of the keratometry mire.

Frequent changes in spectacle cylinder power and

axis.

Increased myopia.

Squeezing of the eyelids to create a pinhole effect. The appearance of halos or starbursts around light

during night-time viewing.

Associated atopic disease

Keratoconus Clinical Signs

External Signs

Munson Sign

Rizzuti PhenomenonRizzuti's sign is appreciated

when a slit lamp beam is

focused on the nasal aspect

of the limbus. When viewed

temporally, the apex of the

cone will be illuminated.

Corneal Protrusion may

cause angulations on the

lower lid when down gaze


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Refractive Signs

Retinoscopic scissors reflex

Increased myopia

Increase in and irregularity of astigmatism


Keratometry signs

Lack of mire parallelism

Mire distortion

Increase in and irregularity of astigmatism


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Slit-lamp Biomicroscopic Signs

Vogt striae

Fleischer ring

Scarring

Increased visibility of nerve fibers

Corneal thinning

Hydrops


Corneal Topography Signs

Compression of mires in affected region

Colour map shows power increased in

isolated area of cone

Inferior superior dioptric asymmetry


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Optical Coherence Tomography Signs

Uneven thickness of the cornea

Increase in the Anterior Chamber Depth

Decentered apex

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.


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Cone Types and Prevalence

Nipple (28.7%) Oval (44.3%) Globus (6.7%)

Source: McMahon TT. Collaborative Longitudinal evaluation of Keratoconus

Update ,AAAO meeting Dec 2006.

Nipple Cone

Central Steepening

Steepest form (Less than 5 mm in Diameter)


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Oval Cone

Displace inferior Steepening

More than 5 mm in Diameter

Keratoglobus

Wider 75 to 90% of cornea (more than 5

mm in Diameter)

Not as steep.


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Pellucid Marginal Degeneration

Inferior Peripheral Thinning

Types of the Keratoconus- Summary


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How to Treat Keratoconus Spectacles

Contacts Soft Standard

Soft Custom

RGP Standard

RGP Custom

Hybrid

Surgery Intacs

Penetrating Keratoplasty

Riboflavin/UV treatment (Cross-Linking) preventprogression of Keratoconus

When to Intervene?

Best Spectacle/Soft CL Acuity 20/30 or

better?

Good tolerance of acuity.

Corneal health is not compromised.

If it isnt broke, dont fix it.

Best Spectacle/Soft CL Acuity worse than

20/30?

Specialized contact lenses.

My opinion, use RGP lenses.


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Corneal Shape affect RGP fitting

Which RGP Design?

Early Keratoconus

Standard RGP

KC RGP

Mid-stage Keratoconus KC RGP

Custom KC RGP

Advanced Keratoconus

Custom KC RGP

Intra-limbal or Scleral RGP


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Golden Rules of Fitting Corneal topography: just a starting point.

Fluorescein patterns

No single method

A successful contact lens fit :

Allows the patient to wear the lens for many

hoursMaximizes vision

Keeps the corneal integrity intact.

Fitting Philosophies

Three point touch design: (ideal fit)

Steep fitting: (apical clearance )

Flat fitting:


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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 lensdiameter.

Igel EE-conus Lens

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).


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Fitting Igel EE-conus Lens

Too high tighten edge lift

reduce OAD

steepen base curve

Too low increase edge liftincrease OAD

flatten base curve

Fitting Igel EE-conus Lens

Centrally fitting the

lens on a nipple

cone better insures

optimal acuity and

comfort.


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Advance Keratoconus K-reading >56D

Normal KC RGP cannot improve Vision

Aware of KC lens

Mini-Scleral Design - MSD

Large RGP (14mm 18mm) very stable lens.

Vaults the cornea, rests on the sclera

improve comfort.

Creates a fluid filled environment. Improve VA with new spherical surface


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Mini-Scleral Design

Fitting Pearls

Tendency to tighten after initial fitting.

Light central touch will increase acuity.

Avoid central staining.

Movement is necessary but slight movement isusually sufficient.

Pay attention to tear flow beneath lens.

The steeper the lens, the smaller OAD and lessmovement.

Dont change too many parameters at once.


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Thank You

Any Question?

Documents

Keratoconus Update and RGP Fitting 2013 KL