Human Factors of XR: Using Human Factors to Design XR Systems
SAANA Classification Explains Intracorneal Ring Segments
1. Forum Keraring, Santa Maria da Feira, 6 May 2011
Feira,
The SA.ANA Classification
Making Sense of Intracorneal
Ring Segments
Rafael I. Barraquer MD, PhD
Titular de la Càtedra “Joaquín Barraquer”
Institut Universitari Barraquer – UAB
Barcelona - SPAIN
3. 1st Author
(year)
Eyes (n) INTACS
Segments
Incision
(technique)
Follow-up
mean
(range)
Refractive change (D =
mean reduction) (± =
Visual change (m=
mean improvement) Published series
(thickness in mm) st. deviation)
Colin 10 As (0.45 inf +0.25 sup) Temporal 12 m (all) DK1=4.6D; DK2=3.6D Dcyl=2.70D (- UCVA m=3L BSCVA Follow-
(2001) 4.00-1.30D) m=2L 1st Eyes Ferrara / Incision Refractive Visual
up
Siganos 19 (A) inferior cone S (2x 0.45) (A)Temporal (sup-inf 11.3 m
impl.) (B) Superior (nas- 24 m)
(1- DK= 1.94 ±3.51D UCVA m=2.5L AVCC Author (n) Keraring (techniqu change (D = change (m=
(2003) 14 (B) central cone (50.8647.63D) m=1.7L (impr. 76% m=1 to mean
temp imp.)
DSE= 1.82 ±3.03D 6L; 12% worse, high Ks) (year) Segments e) mean reduction) mean
(range
Boxer Wachler 74 As (0.30-0.35 inf +0.25 Eje + Cyl (exc. if topo 9 m (1- DI-S: 25.626.60D UCVA m=4L BSCVA m=2L (thickness improvement)
(2003) sup) axis @90º of Cyl) 20 m) DSE=2.43D (-3.89-1.46D) (12% worse) )
in mm)
Hellstedt (2005) 50 As (0.45 inf +0.25 sup) Temporal 6.3±3.2m DK1=4.2D; DK2=3.3D UCVA m=1.0±2.0L BSCVA
(1-12 m) SIA = 2.9 ±2.9D m=2.2±2.3L (10% worse) Siganos[2 26 S (2x160º; + Axis 6m DK = no data UCVA
DSE=2.72D(-2.12+0.66D) 2] (2002) Dcyl=2.22D (- m=1.3L(88.4%)
Levinger 58 S (2x 0.30-0.45); As (1x 0.45 Temporal (Sup if central 12 m DK1=3.44D; DK2=2.74D UCVA m=3L(81%≥2L)
0.15-0.35) (manual) (min.)
4.42-2.20) BSCVA m=2.3L
(2005) inf, only if inf cone & SE<-3.0) cone & SE > -3.75) (all) Dcyl=1.57D (-3.34-1.97D) BSCVA m=0L (20/32
DSE=2.84D (-3.88-1.04D) ±2.0L; 10% worse ≥2L)
DSE=5.80D (- (0.370.60)
6.91-1.11D) (2 explants)
Alió 9 (p-central cone) 4 As (0.45 inf +0.25 sup) Temporal (+ axis) 36 m (36- DK=3.13D @6m (1.69D BSCVA m=2L
(2006) (inferior cone) or (1x 0.45 inf) 48 m) regression @36m) (0.460.66; maintained
DSE=1.45D (-5.40-3.95D) DI- 636m)
S: 7.094.27D Miranda[2 36 S (2x160º; + Axis 6m DK1=9.6D UCVA m≥2L
Alió 20 (A) K≤53D As (0.45 inf +0.25 sup) Temporal (+ axis) 6m DK: (A)=4.30D; (B)=6.19D BSCVA: (A) m=3.8L (B) 3] (2003) (62.352.7D) (77.78%) BSCVA
(2006) 5 (B) K≥54D or (1x 0.45 inf) (all) DSE: (A)=2.81D; (B)=2.25D m= -1.2L (in 3 eyes, 1x
0.25-0.35) topograp (3- 12
DK2=7.5D m≥2L (80.56%)
(significant only in A) implant) hic m) (58.150.6D) (VA worse =
Colin 57 S (2x 0.40-0.45) As Temporal (0º - 6m DK = 4.3 ±2.8D Dcyl= UCVA m≥2L (78% ) BSCVA
(2006) (0.30-0.45 inf +0.25-0.40 sup) 180º) (1-12 m) 1.52 ±1.60D m=2 to 8L (62% ) (6% worse (manual) Dcyl: no data none, 5
≥2L)
DSE= 3.07 ±2.54D DSE=2.49D (- extrusions)
Ertan 118 S (2x 0.25-0.45?) As (0.45 inf Temporal (?) (FsL) 12 m DK=3.90D (51.5647.66D) UCVA m=2L (81.3% )
7.29-4.80D)
(2006) +0.25 sup, inferior cone) DSE=3.85D (-7.57-3.72D) BSCVA m=1.8L (impr. 73.7% ,
worse 9.3%)
Ibrahim 186 S or As (0.25 á + Cyl axis 5 years DK = 4.48D (52.5348.05D) UCVA m=85.2% BSCVA Kwitko 51 S (2x160º; + Axis 13±8. DK =5.69D UCVA m=86.4%
(2006) 0.45) m=87.9% (48.7643.17D) BSCVA m=86.4%
(2004) 0.20-0.30) (manual) 7m
Kanellopoulos 20 As (0.35-0.45 inf +0.25- Temporal (above 6m DK= 3.10D (49.4546.35D) UCVA m=6L Dcyl=1.66D (- (11.7% worse,
(2006) 0.40 sup) horizontal) (6 -12 m) Dcyl=2.54D (-3.75-1.21D) (20/15420/28) BSCVA
3.82-2.16D) 10 extrusions)
Dsph=2.23D(-3.38-1.15D) m=3.5L (20/3720/22)
DSE=3.69D(-5.33-1.64D) DSE=1.53D (-
Rabinowitz 10 (A) manual 20 S (2x 0.35, 15 eyes) As Temporal (?) (A) A: 12 m DK: (A)=2.52D; (B)=2.91D DSE: UCVA: (A) m=3.6L; (B) m=4.1L 6.08-4.55D)
(2006) (B) Lfs (1x 0.35, 4 eyes; 0.35 inf manual (B) FsL B: 6 m (A)=2.96D; (B)=3.98D (N.S.) BSCVA (A) m=1.6L; (B)
+0.25 sup, 1 eye, all FsL) m=3.9L (all n.s.)
Sharma 17 (1x) 20 (2x) (inf. As (1x: 0.25-0.35) ó (2x: + Cyl axis 3m DK1: (1x)=2.76D; (2x)=0.93D DK2: UCVA: (1x) m=9L; (2x)
(2006) cones, incl. post-LASIK 0.30-35 inf, 0.25-0.30 sup) (1 – 13 m) (1x)=0.92D; (2x)=0.13D SIA: m=2.5L BSCVA: (1x) Shabayek 21 S, As + Axis 3m DK1=3.37D; UCVA m=2.5L
ectasia) S (2x 0.35, 1 eye) (1x)=5.69D; (2x)=1.58D
m=2.5L (2x) m<1L DK2=1.21D BSCVA m=1.7L
DI-S: (1x)=9.51D; (2x)=4.22D DSE: (2007) (120º- (FsL) (1-6
(1x)=1.45D; (2x)=2.26D DK =2.24D (70%) (5%
Colin 100 S (2 x 0.40-0.45) Temporal 24 m DK= 3.3D (50.146.8D) UCVA: m=1 to ≥5L (80.5% 160º; m) (48.7946.54D) worse, 1 grade IV
(2007) Dcyl=1.31D (-4.62-3.31D) BSCVA: m=1 to ≥5L
DSE=3.13D (-6.93-3.80D) 68.3% 14.6% worse 1-4L)
0.15-0.35) Dcyl=2.68D (- cone, 1 explant)
Kymionis 11 (A) inferior cone S (2x 0.45) (A)Temporal (sup- 5 years (58- DK= 1.57D (49.59 45.20 @6m UCVA m=2.8L (0-9L)
4.83-2.15D)
(2007) 6 (B) central cone inf impl.) (B) 78 m) 48.02D@60m) BSCVA m=1.4L (0-8L) (6% DSE=2.37D (-
Superior (nas-temp (6m60m change not signific.) worse 3L, 1 eye) 6.33-3.96D)
impl) DK1-K2=0.98D (4.463.48D)
DSE=2.52D (-5.54-3.02D) DK1 =3.93D; DK2
Barraquer 165 S, As + Cyl/K1 6m UCVA m=2.0L
Zare (2007) 30 As (0.35-0.45 inf +0.25- Temporal 6m (all) DK =1.94D (49.8447.90D) UCVA m=3L BSCVA
(unpublished) =2.27D BSCVA m=1.0L
0.40 sup) Dcyl=0.75D (-4.65-3.90D) m=2L (90º-210º; axis (3-27
DSE=3.0D (-6.93-3.23D) Dcyl=2.48D (- (6% worse ≥2L,
Ertan (2008) 306 S (2x 0.25-0.45?) As Temporal (?) (FsL) 10.4 ±5m (4- DK =2.79D (50.7047.91D) UCVA m=2.5L(75.7%) 0.15-0.35) (manual, m) 5.91-3.43D)
(0.45 inf +0.25 sup, inf. 30 m) Dcyl=0.29D (-4.11-3.82D) BSCVA m=2L (71.6% ) (3.7% 5 extrusions)
cone) DSE=3.09D (-7.81-4.72D)
worse ≥2L) FsL) DSE=3.57D (-
Shetty (2008) 14 (stage III cone) S (11 eyes); As (3 eyes 0.45 K1 axis (Orbscan) 6m DK =3.59D (53.0149.42D) UCVA m=1.1L BSCVA 5.21-1.64D)
inf +sup “thinner” ¿?) (1-12 m) Dcyl=1.25D (-4.89-3.64D) m=1.7L (7.14% worse 1L)
DSE=4.20D (-9.13-4.93D)
4. ICS for KC: Results (summary)
summary)
All agree they are “Effective”, BUT…
“Effective”
►Increased UCVA ~ 2 - 3 lines (average)
►Increased BSCVA ~ 1 - 4 lines (~ 2 ave.)
ave.)
►Decreased Spher.Eq.
Spher.Eq. ~ 1.5 – 4.2 D (5.8 w KR)
►Decreased Topo. K
Topo. ~ 1.5 – 4.5 D (8.0 w KR);
►Decreased Refract. Cyl. ~ 0.3 – 2.7 D
Cyl.
[50-
[50-65% ave.: NOT a “REFRACTIVE” procedure]
ave.:
5. ICS for KC: Results (summary)
summary)
But:
►Why incomplete results? How can we improve them?
►Why variable results? Is it a nomogram issue?,
should we follow Topography?, or aberrations-Coma?
aberrations-
►Long term effect? Do they stop KC progression?
Safety: all agree it is “safe”, but:
►BSCVA line LOSS: 3 to 14% of eyes
► 8-20% extrusion (w Keraring manual technique)
6. To Progress:
Progress:
What We Need to Know…
Know…
Mechanism of Action: A better
understanding of the basics of how ICS work
Available Modalities: Organize = Classify
the basic types of implant combinations (to
enable comparisons, studies…)
New/Refined Nomograms ? (later on…)
7. ICS: Mechanism of action?
Commonly assumed to follow
Thickness Law of José I. Barraquer
► The effect does increase with:
Thicker segments
Smaller
HOWEVER:
► They work at deep position
NO anterior lamellar effect
► The impl. meridian is steepened
impl.
► The “open” meridian is flattened
(just the opposite of JIB’s Law !!)
8. ICS: Biomechanical effects !!
Space Occupation ?
► Force lamellae to
“detour” around impl.
impl.
► No forward thickness
effect (deep location),
or only a local “bump”
► Torsional effect?
9. New Options: Increased Complexity
Options:
Multiple types of ICS
(varying diameters,
thickness, arc widths)
greater number of possible
combinations.
Greater control possible
independent effects on
Sphere
Astigmatism
Coma
Other irregularities?
10. ICS:astigmatic vs. sphere effects
Compressive suture-like effect:
suture-
A Sector only (~ 90º)
(~
► steeps that meridian
► flattens @ 90º
► Just the opposite of
“Thickness Law”
► Corrects astigmatism
A Circle ≈360º (180º x2)
► gen. flattening
► Just like a tightly sutured PK
► Corrects myopia only
11. ICS in KC & Corneal Ectasia
¿What are we trying to correct?
Astigmatism? sector ICS
Myopia ? circle ICS
Decentration ?
► Unique of KC & Ectasia
► Cannot correct w glasses
► Measurable as Coma
12. What about Coma ?
How can we correct it ?
• Astigmatism: a quadrant aberration correction:
Astigmatism: correction:
• 90º arc Max Effect
• 2 equal, symmetric, ICS (coupling), centered over flat axis,
equal, symmetric, (coupling),
• Coma: a half circle (hemispheric) aberration correction:
hemispheric) correction:
• 180º arc Max Effect
• 1 ICS only (asymmetric), centered over coma (decentration) axis
asymmetric), (decentration)
13. Implant Options ?
Basic Patterns of ICS implantation
Symmetry:
► 2 equal, paired ICS Symmetric
► 1 single / 2 different ICS (or more) Asymmetric
Axiality:
Axiality:
► ICS (1 or 2) over flat (-) astig. axis Axial
(- astig.
► ICS (1 or more) over an axis different
from flat (-) astigmatism (≥ 30º)
(- Non-Axial
on-
The SA.ANA classification
14. Combining the two criteria: 4+2 types (The SA.ANA classification)
SA.ANA Segments Implantation Axis Frequency
(Symmetric vs. found (n=1097)
type (Axial= same, flat A axis vs. Non-Axial= other axis)
Asymmetric)
Symmetric Axial
SA 2 ICS 9.96%
≈ 80%
(red= plus axis
(equal)
blue= minus axis)
Asymmetric Axial 39.58%
AA1 1 ICS
2 ICS (unequal) (red= plus axis 28.31%
AA2 blue= minus axis) (Total 67.89%)
Symmetric Non-Axial
(green= mid-ICS
SNA 2 ICS axis, displaced ≥ 30º 5.77%
(equal) from minus axis)
Asymmetric Non-Axial 6.16%
ANA1 1 ICS (wide)
(green= mid-ICS axis,
displaced ≥ 30º from 4.98%
ANA2 2 ICS (unequal) Minus axis coma
axis or intermediate) (Total 11.14%)
15. Central, symmetric ectasia/conus
[ also: Regular astigmatism (congenital or post-PK);
Mild myopia (congenital or residual after Rx.)]
red= steep ast. axis
ast.
blue=
blue= flat ast. axis
ast.
coma = minimal
21. AA2 - Asymmetric Axial (2 different ICS)
red= steep ast. axis
ast.
blue= ast.
blue= flat ast. axis
coma = significant,
significant,
towards flat axis
• Same as AA1, BUT:
AA1,
• Higher cylinder or sphere combinations
• Additive effect of ICS thickness/width
thickness/
• Coma corrected by asymmetry
• Upper ICS must be smaller/thinner
smaller/
22. The Albertazzi/Keraring Classification
Albertazzi/Keraring
Nomograms based on cone
eccentricity: 1, 2, 3
Type 1: Very eccentric
“moustache”, coma high but close
to flatter (minus) astigmatism axis
Type 3: Central bowtie, low coma
Type 2: Intermediate the most
difficult because of significant
coma is away from minus axis
(even close to plus axis)
dilemma: Ast. vs.Coma corr.?
Ast.
23. Intermediate ectasia
Paracentral
Relatively orthogonal
Coma towards
steep axis
Difficult choice:
if ICS implant
red= steep ast. axis
ast. @coma axis
blue=
blue= flat ast. axis
ast. will increase
coma = signficant,
signficant, astigmatism &
close to steep axis vice versa
24. SNA Symmetric Non-Axial
Paired axis-displaced ICS
“encroaching” coma axis while
still acting on flat axis
red= steep ast. axis
ast.
blue=
blue= flat ast. axis
ast.
coma = signficant,
signficant,
close to steep axis
25. SNA-
SNA- Symmetric Non-Axial (paired ICS)
Non-
red= steep ast. axis
ast.
blue= ast.
blue= flat ast. axis
coma = significant,
significant,
towards steep axis
• Intermediate ectasia
• Paracentral, relat. orthogonal ectasia
relat.
• Sphere mild/moderate
mild/
• Cylinder moderate/high
moderate/
• Coma towards plus cyl axis
• Paired ICS, usually of 120º
• Inferior displacement 15-30º each
15-
26. Intermediate ectasia
Paracentral – mid-peripheral
mid-
Non-
Non-orthogonal
red= steep ast. axis
ast.
blue=
blue= flat ast. axis
ast.
coma = signficant,
signficant,
towards steep axis
or intermediate
27. ANA1 – Asymmetric Non-Non-
Axial (single wide ICS)
red= steep ast. axis
ast.
blue=
blue= flat ast. axis
ast.
coma = signficant,
signficant,
towards steep axis
or intermediate
28. ANA1-
ANA1- Asymmetric Non-Axial (single ICS)
Non-
red= steep ast. axis
ast.
blue= ast.
blue= flat ast. axis
coma = significant,
significant,
towards steep axis
• Intermediate ectasia
• Paracentral, non-orthogonal ectasia
non-
• Sphere mild
• Cylinder moderate/high
moderate/
• Coma towards plus cyl axis (±)
(±
• Single ICS, usually wide 160º- 210º
160º-
• At coma axis or intermediate
29. ANA2 - Asymmetric Non-Axial (two ICS)
Non-
red= steep ast. axis
ast.
blue= ast.
blue= flat ast. axis
coma = significant,
significant,
towards steep axis
• Intermediate ectasia
• Paracentral, non-orthogonal ectasia
non-
• Sphere moderate/high
moderate/
• Cylinder moderate/high
moderate/
• Coma towards plus cyl axis (±)
(±
• Two ICS: inferior wider (160º) @ coma
• Superior small (90º-120º) @ flat axis
(90º-
31. ANA3 (ANA1 SA) - Triple ICS (2-step)
(2-
red= steep ast. axis
ast.
blue= ast.
blue= flat ast. axis
coma = significant,
significant,
towards steep axis
After 1st ICS: Refr. Astigm. increased to -5 D (7 D by Orbscan Sim K)
Refr. Astigm.
UCVA improved to 0.4 !! (BSCVA: -5@160º = 0.85)
Coma (mostly vertical) reduced from 0.90 mm 0.20 mm (iTrace)
iTrace)
Ectasia pattern changed more central & symmetric
32. ANA3 After adding 2x90ºx150 mm Kerarings…
Kerarings…
UCVA:
@day 1 = 0.65 PLANO
@12 months = 0.95 PLANO
Topography cylinder = 2.6 D (Orbscan Sim K)
Ectasia pattern changed to more central & symmetric
Apparent combination of centering & astigmatic effects in
two stages
33. Intracorneal Segments (ICS) implantation types (The SA.ANA classification)
Type Frecuency
Segments Implantation Axis Indications Examples
SA.ANA (Symmetric or (Axial = same, minus cyl axis
Asymmetric) Non-Axial = different axis)
Central (symmetric) ectasia
Symmetric Axial Regular astigmatism
SA 2 ICS
(equal)
(red= plus cyl
blue= minus cyl)
(congenital or post-PK)
Mild myopia (congenital or ≈ 10%
residual after Rx.)
Asymmetric ectasia (markedly
Asymmetric Axial displaced inferiorly)
AA1 1 ICS Coma ± towards minus cyl axis
(roughly coincident <30º dif.)
≈ 68%
(1 or 2 ICS depending on
AA2 2 ICS (red= plus cyl amount of cylinder/sphere)
(unequal) blue= minus cyl)
Intermediate ectasia
Symmetric Non-Axial (paracentral, relatively
≈ 6%
orthogonal)
SNA 2 ICS (green= mid-ICS
axis, displaced)
Sphere mild/moderate
(equal) Cylinder moderate/high
Coma ± towards plus cyl axis
Intermediate ectasia
Asymmetric Non-Axial (paracentral, non-orthogonal)
Sphere variable
ANA1 1 ICS (wide) Cylinder moderate/high
2 ICS Coma ± towards plus cyl axis
ANA2 (unequal) (inferiorly)
Intermediate ectasia
(peripheral, ± incipient)
≈ 11%
Sphere mild
ANA3 3 ICS Cylinder mild/moderate
(2-step) Coma ± towards plus cyl axis
(almost at 90º of minus axis)
34. Summary
The availability of multiple ICS types demands a
classification to enable a meaningful comparison
between implant series.
Observed ICS implantation modalities (n=1097) allow a simple
while comprehensive classification based on 2 criteria: symmetry
criteria:
& axiality. Combining the 2 criteria results in 4 types:
axiality.
The SA.ANA classification
SA = Symmetrical & Axial (always 2 equal ICS, @same, flat axis) = 9.96%
AA = Asymmetrical & Axial [either 1 (AA1) or 2 (AA2) ICS] = 67.89% (total)
SNA = Symmetrical & Non-Axial (always 2 equal ICS, @different axis) = 5.77%
on-
ANA = Asymmetrical & Non-Axial [either 1 (ANA1) or 2 (ANA2) ICS] = 11.14%
on-
35. Perspectives
Classifiaction (SA-ANA) a tool for outcome comparison
(SA-
opens new possibilities:
► Better classification of keratoconus & other ectasia
► To refine (redefine) indications for ICS
► To develop better ICS nomograms
Testing/confirmation of basic theory (mechanism of action)
Independent address of astigmatism and coma
(decentration), esp. non-axial (ANA) minority? types
decentration), non-
36. Grupo Ibérico de Segmentología
José Alfonso (Oviedo)
Federico Alonso (Sevilla)
Sevilla)
Rafael I. Barraquer (Barcelona)
Margarita Cabanas (Sevilla)
Sevilla)
Antonio Limao (Lisboa)
Lisboa)
Joaquim Murta (Coimbra)
Cristina Peris (Valencia)
Vicente Rodríguez (Las Palmas)
Pedro Tañá (Alicante)
y con el apoyo de