Dr. Barraquer's Abu Dhabi presentations: 1

New Options in the Treatment of Keratoconus Mechanism of Ac.on of Intracorneal Ring Segments Rafael I. Barraquer, MD, PhD Medical Director Barraquer Ophthalmology Center Barcelona, SPAIN

Management of Keratoconus • Traditional options – (Spectacles), RGP-CL – Special CL (piggyback, hybrid)

– Keratoplasty (penetrating)

• Prevention ?

• Current options

– (Spectacles), RGP-CL Special CLs

– IntraCorneal Ring Segments (ICRS) – Collagen Crosslinking (CXL) – MW-Thermokeratoplasty (Avedro) – Combined CXL +ICRS, PRK, pIOL, etc.

– Keratoplasty: • Penetrating ?

• Deep lamellar (DALK)

• Prevention – Avoid eye rubbing !!

– Genetic counseling?

Historical Background

“Refrac've Keratoplasty” (José I. Barraquer, 1949)

Peripheral Annular Resec.on

For: • Keratoconus • Anisometropia

• “Corrects ~ -­‐10 D”

Thickness-Curvature 18 types of procedures Relation (1964) Â Â

“Thickness’ Law” of J.I.B. (1965) Thickness CENTRAL

PERIPHERAL

INCREASE DECREASE

Steepens (KPh-H)

Flattens (KPh-M)

Flattens (KM-M)

Steepens (KM-H)

Annular Implants (J.I.B, 1964)

Homoplastic rings by E.D. Blavatskaya Inst. Filatov, Odessa, 1966

• • • • •

Experimental (rabbits) Homoplastic implants Lamellar corneal pocket Relat. superficial (“medium” thickness) “Ideal” rings 7.0 x 4.0 mm

Homoplastic Annular Implants

by E.D. Blavatskaya

• ↑↑Thickness ↑↑Flattening – 100-120 mm è 6 - 8 D – 150-170 mm è 9 -12 D – 290-310 mm è 18 - 21 D

• ↑↑Diameter ↓↓Flattening (w constant thickness)

• Irregular astigmatism Zhivotovsky & Vishnevetsky (1969-71) n 2 human cases: plastic 7-5 mm intracorneal rings è corr. high myopia (“good results” @ 2 a.)

Silicone Rubber Rings (G.Sim贸n & R.I.Barraquer, 1985-88)

Rectangular section rings Flat configuration - adaptable Various: thickness & diameter

Technique: corneal pocket Experimental (rabbits, dogs)

Silicone rings

(Simón & Barraquer)

Simple procedure Can induce marked flattening Good tolerance Increasing effect with ► Ring thickness ► Smaller diameter

Keratophakia  for Myopia Ring

Posi.ve (corr. H) Nega.ve (corr. M)

BUT: Thickness law works…  Only if implant (or ablation) is SUPERFICIAL !

Superficial implants

è Push forward the anterior face (thickness effect)

Deep implants è Deform the posterior face (& not directly the anterior face)

è Thickness Law does not apply

Current ICRS are implanted at a deep stromal level

Ø

Indentation is basically backwards

Ø

No push-forward effect (would-be “thickness” effect)

Ø

What then?  something “Biomechanic”

Mechanism of Action of Intracorneal Segments

(“Rings”)

ICR: PMMA Ring (closed) by Fleming & Schanzlin, 1987

Experimental (rabbits) Expandable (metal clamp closure) Prismatic – Hexagonal Profile Conic conf. (parallel to lamellae)

Theory/Mechanism: • Expansion è flat, M • Compression è steep, H

Ring Segments (INTACS)

Clinical application: • Myopia (W. Nosé et al., 1991-93-96) èEffective: 1,25 – 3,25 D • Keratoconus (J. Colin, 1997)

Ferrara Ring -Keraring® Arcuate Implants (P. Ferrara, 1991…)

Triangular section è Posterior base

Flat configuration è Not parallel to lamellae

Gel Injection Ring (Polyethylene) (GIAK, Sim贸n, Parel et al., 1994)

ICRS: Mechanism of action? n Nobody really knows how they work

• Pseudo-Thickness Law – The effect does increase with ring thickness & small Æ, BUT: – The impl. meridian is steepened – The “open” meridian is flattened (just the contrary of JIB’s Law !!

• NOT related to Thickness Law of José I. Barraquer – Not a negative keratophakia – They work at deep position è NO anterior lamellar effect

Biomechanical effects • Space Occupation !!

– Force lamellae to “detour” around impl.

– No forward thickness effect (deep location), or only a local “bump” – Torsional effect?

Space Occupa.on = Compression Similar to: • Compressive sutures • Wedge resection (sutured) • Thermokeratoplasty (tissue retraction)

Sector vs. circular effects • Assuming a compressive effect (on the detoured collagen lamellae)

•  Increased tension

• When acting over a sector only… è that axis will be steepened è the opposite axis @90º will be flattened (coupling effect) • This corrects Astigmatism • This sector action is maximal with the less wide segments (90º) • The effects of two opposite implants are additive • This action is the opposite of what Barraquer “Thickness Law” would predict

However, when compression is circular…

If compression is 360º: è Gen. flattening !!

Just like a tightly sutured PK Corrects mostly myopia

Now, there MUST be a point where steepening (sector compression) effect gives way to flattening (circular compression) effect This should be observed as we go from narrow ( 60º, 90º) to progressively encircling (2 x160º, etc.) segments

Remember… q Early ICRS (1990s) were conceived to correct myopia q 2 equal, encircling implants

q Current uses:  Keratoconus, Ectasia  1 single or 2 unequal implants

ICRS in KC & Ectasia

¿What are we trying to correct?

• As.gma.sm • Myopia • Decentered op.cs – Typical of KC & other Ectasia – Not corrected by glasses – Can be measured as Coma

¿How can we correct Coma?

• Astigmatism: • •

•

a Quadrant aberration

Maximal correction  action over 90º 1 or 2 ICRS centered over the flat axis. There is coupling

Coma: a Hemispheric aberration Maximal correction  action over 180º • 1 ICRS only centered over Coma/decentration axis . No coupling •

Summary Ø Ø Ø

Ø

Corneal “ring” procedures: can be traced to pioneering refractive surgery (1949) Intracorneal deep annular implants do not follow thickness law  biomechanical ection Compressive “lamellar detour” theory explains observed effects of ICRS: Ø asymmSector implants steepen axis, flatten opposite axis(correct astigmatism) Ø Circular implants correct mostly sphere (myopia) Ø Wide etric implants correct decentration/coma (properly placed) New versatile implants of different width /diameter/ thickness promise selective correction of the differing features in KC & other ectasia.

Thank You