Ferrara Ring Nomogram Leonardo Torquetti, MD, PhD.

Ferrara Ring NomogramLeonardo Torquetti, MD, PhD

FERRARA RING NOMOGRAMFERRARA RING NOMOGRAM

First generation (1997 - 2002): keratoconus gradeFirst generation (1997 - 2002): keratoconus grade

Second generation (2002 - 2006): spherical Second generation (2002 - 2006): spherical equivalentequivalent

Third generation (2006 - 2009): topographic Third generation (2006 - 2009): topographic astigmatismastigmatism

Fourth generation (May 2009 to now): Fourth generation (May 2009 to now): asphericity (Q)asphericity (Q)

Evolution of the NomogramEvolution of the Nomogram(criteria for ring selection)(criteria for ring selection)

FERRARA RING NOMOGRAMFERRARA RING NOMOGRAM

Second generation (2002 - 2006): spherical Second generation (2002 - 2006): spherical equivalentequivalent

Eye 1Eye 1 Eye 2Eye 2

Refraction: -10.00 DRefraction: -10.00 D Refraction: -10.00 DRefraction: -10.00 D

Are these the same?Are these the same?

NO !NO !cornea hypercorrection in axial myopia cornea hypercorrection in axial myopia

FERRARA RING NOMOGRAM

Third generation (2006 - 2009): topographic Third generation (2006 - 2009): topographic astigmatismastigmatism

Eye 1Eye 1 Eye 2Eye 2

Keratometry: 42.00 x 47.00 DKeratometry: 42.00 x 47.00 D

Are these the same ?Are these the same ?

NO !NO !same topographic astigmatism - different changes after ring same topographic astigmatism - different changes after ring

implantationimplantation

Keratometry: 52.00 x 57.00 DKeratometry: 52.00 x 57.00 D

ASPHERICITY (Q)

CORNEAL ASPHERICITY

OblateOblate HyperprolateHyperprolateProlateProlate

00 -1-1 -2-20,50,5 -0,23-0,23

HOW THE FERRARA RING WORKS

Nowadays:

Asphericity law

Addition in the cornea periphery = asphericity change – frequently without concomitant significant corneal flattening;

Ring diameter = how much the cornea will be flattened, the astigmatism and asphericity will be changed

Ring arc length = how much the asphericity, keratometry and astigmatism will be changed. The shorter the segment, the greater the astigmatic correction, the lesser the asphericity change.

140 arc = PMD140 arc = PMD - Q 0 or positive- Q 0 or positive

- Low K values- Low K values - High astigmatism- High astigmatism

210 arc = Nipple210 arc = Nipple - Q negative (hyperprolate cornea)- Q negative (hyperprolate cornea)

- High K values- High K values - Low astigmatism- Low astigmatism

160 arc = 90% of keratoconus (“standard” ring)160 arc = 90% of keratoconus (“standard” ring) - Q negative (prolate to hyperprolate cornea)- Q negative (prolate to hyperprolate cornea)

- Average to high K values- Average to high K values - Average to high astigmatism- Average to high astigmatism

General GuidelinesGeneral Guidelines

NOMOGRAM

IT MUST BE DETERMINED:

1. The type of keratoconus:Central NippleOval (paracentral)PMD

2. The corneal asphericity (Q) or K (average)

3. The pachymetry at the corneal steepest axis and probable ring track (5 mm optical zone)

1. Type of keratoconus1. Type of keratoconus

NOMOGRAM

CentralCentral(Nipple(Nipple))

OvalOval

Oval ConesOval Cones

NOMOGRAM

Q (asphericity) variation according to ring thickness

QQ

Q (asphericity) and K (keratometry)variation according to ring thickness

Single Segments (µm)Single Segments (µm) ∆∆Q Q ∆∆KK pp value value

150150 - 0.07 - 0.07 0.78 D 0.78 D 0.0420.042

200200 - 0.31- 0.31 1.82 D1.82 D < 0.001< 0.001

250250 - 0.34- 0.34 2.74 D 2.74 D < 0.001< 0.001

Paired Segments (µm)Paired Segments (µm)  

150 – 150 150 – 150 - 0.57- 0.57 3.40 D3.40 D < 0.001< 0.001  

150 – 200 150 – 200 - 0.73- 0.73 4.35 D4.35 D < 0.001< 0.001  

150 – 250 150 – 250 - 0.80- 0.80 3.86 D 3.86 D 0.0010.001  

200 – 200 200 – 200 - 0.86- 0.86 5.65 D5.65 D < 0.001< 0.001  

200 – 250 200 – 250 - 1.02- 1.02 6.27 D 6.27 D < 0.001< 0.001  

250 – 250250 – 250 - 0.99- 0.99 5.30 D 5.30 D 0.0010.001  

NOTE: (THIS IS VALID FOR ALL MAPS)

The segment or pair of segments SHOULD not turn the expected postoperative cornea asphericity (Q) significantly below -0.23.

If this happens so it is advisable to choose a pair of segments that fits this condition even if the achieved KERATOMETRICcorrection is smaller than the desired one.

AVOID POSTOPERATIVE OBLATE AVOID POSTOPERATIVE OBLATE CORNEAS !CORNEAS !

Q (asphericity) = Quality of visionQ (asphericity) = Quality of vision

Correlation between ∆K, ∆Q and Pachymetry

Nipple

NOMOGRAM

Q change induced by the 210 Q change induced by the 210 ringring

210/150 - 0.36210/150 - 0.36210/200 - 0.60210/200 - 0.60210/250 - 0.82 210/250 - 0.82

Nipple ConesThe 210 ring

Nipple Cones

NOMOGRAM

The “lake” in the Elevation Map is characteristic of Nipple KonusThe “lake” in the Elevation Map is characteristic of Nipple Konus

Nipple Cones

Pellucid Marginal Degeneration

NOMOGRAM

IT MUST BE DETERMINED:IT MUST BE DETERMINED:

The pachymetry at the corneal steepest axis and probable ring track The pachymetry at the corneal steepest axis and probable ring track (5 mm optical zone)(5 mm optical zone)

Incision (80% depth):Incision (80% depth):1 segment: at 901 segment: at 9000 axis – the tip of the ring at the steepest axis – the tip of the ring at the steepest

axisaxis2 segments: at the steepest axis2 segments: at the steepest axis

NOMOGRAM

WHY THE INCISION SHOULD BE AT 80% DEPTH?

NOMOGRAM

Superficial stromaSuperficial stroma Deep stromaDeep stroma

NOTE: (THIS IS VALID FOR ALL MAPS)

The thickest segment of a pair of segments cannot exceed half thickness of the cornea in its bed.

If this happens so one has to choose a pair of segments that fits this condition even if the achieved correction is smaller than the desired one.

IncisionIncision544 micra544 micra

superiorsuperior inferiorinferior

SUMMARYGENERAL RULES

NOMOGRAM

Q preoperative Q preoperative -- Q change induced by the ring = - 0.23 (TARGE FINAL Q = - 0.23 (TARGE FINAL Q VALUE)VALUE)

ASPHERICITYRING SELECTION

NOMOGRAM

Oblate corneas (Q < -0.23): single 140 or 160 (arc) segments

Moderately prolate corneas (- 0.23 < Q < -1.00): single or paired 160 (arc) segments

Hyperprolate corneas (Q > - 1.00): paired 160 (arc) segments or 210 segment if nipple cone

The asphericity is the best parameter, at the The asphericity is the best parameter, at the present moment, for ring selection;present moment, for ring selection;

There is a tendency to implant “less” tissue to There is a tendency to implant “less” tissue to achieve the same (or better) correction than was achieve the same (or better) correction than was achieved in the past;achieved in the past;

Q value = value = Quality of visionuality of vision

NOMOGRAM

THANK YOU!THANK YOU!

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