1. Ferrara Ring Nomogram
Leonardo Torquetti, MD, PhD

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

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

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

5. ASPHERICITY (Q)

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

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. 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

9. 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)

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

11. NOMOGRAM
Oval Cones

12. Q (asphericity) variation according to ring thickness

13. 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

14. 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
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

15. Correlation between ∆K, ∆Q and Pachymetry

16. Q change induced by the 210 ring
NOMOGRAM
Nipple
Q change induced by the 210 ring
210/
210/
210/

17. Nipple Cones
The 210 ring

18. NOMOGRAM
Nipple Cones

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

20. Pellucid Marginal Degeneration
NOMOGRAM
Pellucid Marginal Degeneration

21. 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

22. NOMOGRAM WHY THE INCISION SHOULD BE AT 80% DEPTH? 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.

25. Incision
544 micra

26. superior
inferior

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

28. NOMOGRAM ASPHERICITY RING SELECTION
Oblate corneas (Q < -0.23): single 140 or 160 (arc) segments
Moderately prolate corneas ( < Q < -1.00): single or paired 160 (arc) segments
Hyperprolate corneas (Q > ): paired 160 (arc) segments or 210 segment if nipple cone

29. 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

30. THANK YOU!