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Ferrara Ring Nomogram Leonardo Torquetti, MD, PhD.

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Presentation on theme: "Ferrara Ring Nomogram Leonardo Torquetti, MD, PhD."— Presentation transcript:

1 Ferrara Ring Nomogram Leonardo Torquetti, MD, PhD

2 FERRARA RING 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 Evolution of the Nomogram (criteria for ring selection)

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

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

5 ASPHERICITY (Q)

6 CORNEAL ASPHERICITY Oblate HyperprolateProlate 0-20,5-0,23

7 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.

8 140 arc = PMD - Q 0 or positive - Q 0 or positive - Low K values - High astigmatism - High astigmatism 210 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) - 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

9 General Guidelines NOMOGRAM 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)

10 1. Type of keratoconus NOMOGRAM Central (Nipple ) Oval

11 Oval Cones NOMOGRAM

12 Q (asphericity) variation according to ring thickness Q

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

14 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 ! AVOID POSTOPERATIVE OBLATE CORNEAS ! Q (asphericity) = Quality of vision Q (asphericity) = Quality of vision

15 Correlation between K, Q and Pachymetry

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

17 Nipple Cones The 210 ring

18 Nipple Cones NOMOGRAM

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

20 Pellucid Marginal Degeneration NOMOGRAM

21 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 90 0 axis – the tip of the ring at the steepest axis 2 segments: at the steepest axis NOMOGRAM

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

23 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.

24

25 Incision 544 micra

26 superior inferior

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

28 ASPHERICITY RING 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

29 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; value = uality of vision Q value = Quality of vision NOMOGRAM

30 THANK YOU! leotorquetti@gmail.com leotorquetti@gmail.com


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