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Ferrara Ring: Nomogram
Transcript of Ferrara Ring: Nomogram
variation according to ring thickness
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. HOW THE FERRARA RING WORKS AVOID POSTOPERATIVE OBLATE CORNEAS !
Q (asphericity) = Quality of vision Segment thickness (160 – arc) Q Q (asphericity) variation according to ring thickness
ASPHERICITY (Q) Keratometry: 52.00 x 57.00 D NO !
same topographic astigmatism - different changes after ring implantation Are these the same ? Keratometry: 42.00 x 47.00 D Eye 2 Eye 1 Third generation (2006 - 2009): topographic astigmatism FERRARA RING NOMOGRAM 160 arc = 90% of keratoconus (“standard” ring)
- Q negative (prolate to hyperprolate cornea)
- Average to high K values
- Average to high astigmatism 210 arc = Nipple
- Q negative (hyperprolate cornea)
- High K values
- Low astigmatism 140 arc = PMD
- Q 0 or positive
- Low K values
- High astigmatism -0,23 0,5 -2 -1 0 Prolate Hyperprolate Oblate CORNEAL ASPHERICITY NO !
Cornea overcorrection in axial myopia Are these the same? Refraction: -10.00 D Eye 2 Second generation (2002 - 2006): spherical equivalent FERRARA RING NOMOGRAM The evolution of the nomogram ASPHERICITY 2002 2006 2009 1997 General Guidelines General Guidelines
Nomogram IMPORTANT Nipple Oval cones PMD Pachymetry IMPORTANT SUMMARY