Embed Size (px)
Citation preview
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
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
