Ferrara Ring Nomogram Leonardo Torquetti, MD, PhD

Evolution of the Nomogram FERRARA RING NOMOGRAM First generation (1997 - 2002): keratoconus grade Second generation (2002 - 2006): spherical equivalent Third generation (2006 - 2009): topographic astigmatism Fourth generation (May 2009 to now): asphericity (Q) Evolution of the Nomogram (criteria for ring selection)

cornea hypercorrection in axial myopia Second generation (2002 - 2006): spherical equivalent FERRARA RING NOMOGRAM Eye 1 Eye 2 Refraction: -10.00 D Refraction: -10.00 D Are these the same? NO ! cornea hypercorrection in axial myopia

Are these the same ? NO ! FERRARA RING NOMOGRAM Third generation (2006 - 2009): topographic astigmatism FERRARA RING NOMOGRAM Eye 1 Eye 2 Keratometry: 42.00 x 47.00 D Keratometry: 52.00 x 57.00 D Are these the same ? NO ! same topographic astigmatism - different changes after ring implantation

ASPHERICITY (Q)

CORNEAL ASPHERICITY 0,5 -0,23 -1 -2 Oblate Prolate Hyperprolate

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.

160 arc = 90% of keratoconus (“standard” ring) - Q negative (prolate to hyperprolate cornea) - Average to high K values - Average to high astigmatism 140 arc = PMD - Q 0 or positive - Low K values - High astigmatism 210 arc = Nipple - Q negative (hyperprolate cornea) - High K values - Low astigmatism

NOMOGRAM General Guidelines IT MUST BE DETERMINED: 1. The type of keratoconus: Central Nipple Oval (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)

NOMOGRAM 1. Type of keratoconus Central (Nipple) Oval

NOMOGRAM Oval Cones

Q (asphericity) variation according to ring thickness

Q (asphericity) and K (keratometry) variation according to ring thickness Single Segments (µm) ∆Q ∆K p value 150 - 0.07 0.78 D 0.042 200 - 0.31 1.82 D < 0.001 250 - 0.34 2.74 D Paired Segments (µm)   150 – 150 - 0.57 3.40 D 150 – 200 - 0.73 4.35 D 150 – 250 - 0.80 3.86 D 0.001 200 – 200 - 0.86 5.65 D 200 – 250 - 1.02 6.27 D 250 – 250 - 0.99 5.30 D

If this happens so it is advisable to choose a pair of segments that 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 KERATOMETRIC correction is smaller than the desired one. AVOID POSTOPERATIVE OBLATE CORNEAS ! Q (asphericity) = Quality of vision

Correlation between ∆K, ∆Q and Pachymetry

Q change induced by the 210 ring NOMOGRAM Nipple Q change induced by the 210 ring 210/150 - 0.36 210/200 - 0.60 210/250 - 0.82

Nipple Cones The 210 ring

NOMOGRAM Nipple Cones

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

Pellucid Marginal Degeneration NOMOGRAM Pellucid Marginal Degeneration

NOMOGRAM IT MUST BE DETERMINED: The pachymetry at the corneal steepest axis and probable ring track (5 mm optical zone) Incision (80% depth): 1 segment: at 900 axis – the tip of the ring at the steepest axis 2 segments: at the steepest axis

NOMOGRAM WHY THE INCISION SHOULD BE AT 80% DEPTH? Superficial stroma Deep 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.

Incision 544 micra

superior inferior

NOMOGRAM SUMMARY GENERAL RULES Q preoperative - Q change induced by the ring = - 0.23 (TARGE FINAL Q VALUE)

NOMOGRAM ASPHERICITY RING SELECTION 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

NOMOGRAM The asphericity is the best parameter, at the present moment, for ring selection; There is a tendency to implant “less” tissue to achieve the same (or better) correction than was achieved in the past; Q value = Quality of vision

THANK YOU! leotorquetti@gmail.com