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Ahmed El-Massry M.D.

Professor of Ophthalmology

Alexandria University

Egypt

No Financial interest ESOIRS 2013

ASCRS 2013

Acknowledgement

Dr. Mones Abdalla

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History

The concept of adding tissue in the periphery

of the cornea to reshape its curvature was

introduced earlier by Barraquer in 1949.

In 1986, Ferrara, initiated the use of ICRs to

moderate and high myopia.

In 1995, a phase II clinical trial (FDA) began using

intrastromal corneal ring segments by Keravision

Inc.

In 1999, Approved by the FDA for myopia of -1.00

to -3.00 diopters (D) and thus received the name

Intacs. by Addition Technology Inc.,.

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MECHANISM OF ACTION

When material is

removed from the

central area of the

cornea or added to

the periphery:

a central flattening

effect is achieved

Mechanism of Action

Shorten the corneal cord length → flattening of the

entire cornea maintaining its +ve asphericity.

El-Massry

Mechanism of action (cont)

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Mechanism of Action (cont):

For correction of astigmatism, the base of each

segment can produce a traction force on the

surface, leading to a further flattening on its axis of

reference.

This causes:

1- Corneal apex displacement towards the

center.

2- Preservation of corneal Asphericity .

3- reduced surface irregularity.

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Indications:

The main indications for the use of ICRs had

steadily increased aiming for :

Correcting Irregular Corneas :

1- Keratoconus.

2- Pellucid marginal degeneration.

3- Post lasik ectasia..

4- Irregular astigmatism after penetrating

keratoplasty,

5- Irregular astigmatism after radial

keratotomy.

6- After corneal trauma on uneven surfaces.

Inclusion criteria for ICRS in KC:

- Clear central cornea.

- Best corrected visual acuity (BCVA)of ≥0.05

- Contact lens intolerant.

- Corneal thickness not less than 400 μ m in the

area of insertion.

.

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Inclusion criteria for ICRS (cont):

- - Maximum keratometric readings <64 D

- Spherical equivalent >-3 D

-Base of the cone, by posterior float using

pentacam, was within 5mm optical zone.

Contraindications

• Severe atopic disease.

• Presence of active infection.

• Autoimmune disease systemic or localized.

• Recurrent corneal erosion syndrome.

• Corneal scarring & Hydrops.

• Extensive corneal dystrophies.

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TYPES:

INTACs (Addition Technology, Inc, Fremont,CA)

KERA ring (Mediphacos, Belo Horizonte, Brazil) .

150° ring segments

PMMA

Hexagonal CS

6.8 mm

8.1 mm

Sizes (mm) 0.250, 0.300, 0.350, 0400, 0.450

Original Intacs

El-Massry

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ICR : Mode of Action

Safest Optical Zones

6.0mm Optical Zone

7.0mm Optical Zone6

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Kera Rings: PMMA :

•A triangular cross section of

600 μ m.

•Thickness ranging from 150 to

350 μ m.

• Has arc length variable (90 ° ,

120 °,150 °, 160 ° , 210 ° and

240 ° ).

•There are two models, the SI5

(optical zone of 5.0 mm) and

SI6 (optical zone of 5.5 mm or

6.0 mm)

Kera rings: It changes the contour of the corneal

surface but not by pushing out on the edge

of the cornea like Intacs.

It simply flattens the cornea . Its apex act like

a pivot for corneal stromal tissue.

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The Differences:

• Kera rings correct a high myopia : 4.8mm vs.

> 6.0mm in INTACs.

• Shape – Kera shape is triangular shape.

• Kera have rounded edges vs sharper edges.

• Keratacs have an arc

Of 320º vs Intacs of 300º

Pre-surgical planning:

Step 1 : Corneal topography and manifest refraction.

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Step 2:

Incision Placement & Verification : Locate and verify positive cylinder axis for incision

placement:

Posterior Float,

Pachymetry.

Peripheral Flattening

Comatic axis

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Step 3 : Select segment using proper Nomogram.

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Depth of insertion :

Pachymetry at the site of

insertion is verified by

using U/S pachymetry

and anterior segmant

OCT.

insertion to 66%, 70%, 75% and 80% depth.

Leaving at least 100 µ residual stromal bed.

The difference between the inner & outer

depth was adjusted in laser settings

according to OCT measurements.

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The incision along the topographic axis of positive cylinder (slit lamp).

the centre of the cornea marked geometrically.

75% depth at 7mm OZ using ultrasound pachymetry

Pocketing on either side of the incision

Globe fixation with a vacuum centering guide. Two intrastromal channels were created .

Two 450 microns equal PMMA segments were implanted. 10-0 Nylon sutures.

El-Massry

Intacs with mild corneal

haze few days after CXL

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Mechanical Intacs

Mechanical Intacs

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Complications of mechanical

Tunnel creation:

Epithelial defects.

Perforation.

Infectious keratitis.

Shallow or asymmetric segment placement.

Corneal stromal edema around the incision.

Extension of the incision toward the central visual

axis or the limbus ,

Unpredictable tunnel depth and persistent incisional

gaping.

Decentration,

Extrusion.

Ring migration.

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Complications are minimized as tunnel

creation now can be carried out with the

femtosecond laser.

Implementation in the Femtosecond laser:

Procedure:

1.) Femtosecond laser cut:

a) Tunnel

b) Access

2.) Insertion of the Rings.

Advantages

(all femtosecond-systems):

- Arbitrary diameter.

- Controlled width of the tunnel.

- Selectable/controlled depth.

- Defined access cut.

- different depth inside/outside

(e.g. for back-plane parallel ICR)

- tunnel segments < 360° (90° - 270°)

(e.g. for asymmetric Keratoconus)

- shape of access

- 1 or 2 access ports

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Tailor-made incisions

- Inner diameter of ring tunnel.

- Outer diameter of ring tunnel.

- Incision depth of inner ring tunnel.

- Incision depth of outer ring tunnel.

- Anterior width of access incision.

- Posterior width of access incision.

- Number of tunnel access incisions ( 1, 2)

Fig. 1 Front view of the eye with

tunnel and access incisions

Fig. 2 Side view of the section of the

cornea with tunnel incision sections

Fig. 3 Sections of the cornea

in the access incision plane

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The procedure.

ASSOCIATION OF ICRs AND CROSS-

LINKING

Few studies combining the two

techniques described so far.(Coskunseven et

al. 2009 , Wollensak et al., Ertan et al. )

Greatest effect with the addition of cross-

linking treatment.

Initially, it can function as a simple additive

effect.

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Anterior segment OCT for

femtosecond laser assisted ICRS

CONCLUSIONS:

- Rate of Complications is higher in the

mechanical group.

- Faster rehabilitation period in

Femtosecond laser group

- ICRs using either mechanical or femtosecond

laser; provide similar visual and refractive

outcomes

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