Transcript CH and CRF

Analysis of Corneal Biomechanical
Properties in Keratoconus Using
Ocular Response Analyzer
Hyuck Jin Choi, Joo Youn Oh, Won Ryang Wee, Mee Kum Kim,
Ji Won Kwon, Sang Mok Lee, MD, Jin Seok Choi, MD
Department of Ophthalmology, Seoul National University College of Medicine, Seoul,
Korea
Seoul Artificial Eye Center, Seoul National Univerisity Hospital Clinical Research Institute,
Seoul, Korea
Financial Disclosure
 The authors of this poster have no financial
interest in the subject matters.
Introduction
Biomechanical Properties of Cornea
•Hysteresis
•A property of physical systems that do not instantly follow the forces
applied to them, but react slowly, or do not return completely to theior
original state
•Etymology: ‘ late, fall short’ in ancient Greek
•Corneal Hysteresis (CH)
•The the difference between the inward (P1) and outward (P2)
pressure values obtained during the dynamic bi-directional
applanation process employed in the Ocular Response Analyzer, as a
result of viscous damping in the cornea.
•P1 – P2
•Corneal Resistance Factor (CRF)
•the overall resistance of the cornea, including both the viscous and
elastic properties (total visco-elasticity)
•P1 – 0.7 x P2
Ocular Response
Analyzer
Introduction
Biomechanical Properties of Cornea
•Corneal-compensated intraocular pressure (IOPcc)
•Less affected by corneal properties than other tonometry
•P2 – 0.43 x P1
•Goldmann-correlated intraocular pressure (IOPg)
•the overall resistance of the cornea, including both the viscous and elastic
properties (total visco-elasticity)
•P1 – 0.7 x P2
Previous Studies
•Normal Value of CH, CRF
•CH = 10.8 ±1.5 mmHg, CRF = 11.0 ±1.6 mmHg (n=165)
(Ortiz et al. IOVS 2007)
•CH = 10.9 ±1.6 mmHg, CRF = 11.0 ±1.6 (n=70)
(Kirwan et al. Ophthalmologica 2008)
•Keratoconus, Post-LASIK
•CH and CRF ⇒
low
(Shah et al. IOVS 2007, Pepose et al. AJO 2007,
Susan et al. BJO 2008, Kerautret et al. JCRS 2008)
Purpose
 To assess the correlation between corneal
biomechanical properties such as corneal
hysteresis(CH) or corneal resistance factor(CRF)
measured by the Ocular Response Analyzer(ORA)
and topographic parameters measured with ORB
scan
Methods
Subjects
•Period of data collection
•June 1, 2008 – September 31,
2008
•Outpatient clinic, Seoul
National University Hospital
•Inclusion criteria
•Subjects who met keratoconus
index
•Control group
•Age and sex-matched normal
eyes
Items
Central
Curvature
I-S index
Corneal
Asymmetry
Value
Suspect
47.2
< < 48.7 D
Positive
> 48.7 D
Suspect
1.4 < < 1.9
D
Positive
> 1.9 D
6mm
Positive
>3D
Difference
Positive
> 0.92 D
K reading
3mm
Modified Rabinowits Keratoconus Index
Parameters
•Ocular Response Analyzer
•Corneal hysteresis(CH), corneal resistance factor(CRF), cornealcompensated IOP(IOPcc), Goldmann-correlated IOP(IOPg)
•ORB scan
•Central curvature, I-S 3mm, I-S 6mm, SimK Max, SimK min, Simk astig,
3mm irregular astig, 5mm irregular astig, CCT
Results
1. Subject Characteristics
KC
Control
Subjects
16
14
Eyes
27
28
11/5
9/5
0.630
Age (yrs)
30.0 ±7.4
27.0 ±1.7
0.142
Eye (R/L)
12 / 15
14 / 14
0.789
Gender (M/F)
P value
Fisher’s exact test;
Mann-Whitney U test
2. ORA between KC and Control
(mmHg)
CH, CRF
IOP
CH
CRF
CH-CRF
CH/CRF
KC
7.8 ±1.5
7.1 ±1.7
0.8 ±0.9
1.1 ±0.1
Control
10.0 ±1.6
9.8 ±1.4
0.2 ±0.9
1.0 ±0.1
P value
<0.001
<0.001
0.020
0.003
(mmHg)
IOPcc
IOPg
IOPcc-IOPg
IOPcc/IOPg
KC
15.4 ±2.5
11.6 ±3.1
3.8. ±1.7
1.4±0.2
Control
15.6 ±3.0
14.6 ±2.6
1.1±1.6
1.1±0.1
P value
0.966
<0.001
<0.001
<0.001
Results
3. . Correlation Analysis in KC
CH – CRF
CH-CRF vs.
CH / CRF
r
P value
Central Curvature
0.357
0.068
I-S 3mm
0.257
I-S 6mm
r
P value
Central Curvature
0.347
0.076
0.196
I-S 3mm
0.259
0.191
0.255
0.198
I-S 6mm
0.169
2. ORA between KC0.272
and Control
Simk Max
0.450
0.019
Simk Max
0.435
0.023
Simk min
0.433
0.024
Simk min
0.429
0.025
Simk Astig
0.280
0.157
Simk Astig
0.260
0.191
3mm Irregular astig
0.415
0.031
3mm Irregular astig
0.421
0.029
5mm Irregular astig
0.552
0.003
5mm Irregular astig
0.553
0.003
CCT
-0.394
0.042
CCT
-0.420
0.029
CH, CRF
CH/CRF vs.
Spearman’s correlation coefficient
Results
3. . Correlation Analysis in KC
IOPcc-IOPg
IOPcc-g vs.
IOPcc/IOPg
r
P value
Central Curvature
0.010
0.615
I-S 3mm
0.011
I-S 6mm
IOPcc/g vs.
r
P value
Central Curvature
0.283
0.186
0.955
I-S 3mm
0.181
0.365
0.222
0.265
I-S 6mm
0.267
0.179
Simk Max
0.040
0.843
Simk Max
0.263
0.185
Simk min
0.212
0.289
Simk min
0.378
0.052
Simk Astig
-0.185
0.356
Simk Astig
-0.004
0.986
3mm Irregular astig
0.077
0.704
3mm Irregular astig
0.258
0.194
5mm Irregular astig
0.157
0.435
5mm Irregular astig
0.337
0.085
CCT
-0.509
0.007
CCT
-0.510
0.007
Spearman’s correlation coefficient
Discussion
Corneal biomechanical changes in keratoconus
• B oth CH and CRF in keratoconus ⇒ lo w er than normal control
• CRF decreased more than CH.
• As corneal thicknessdecreases, biomechanical stability decreases
Combined parameters in keratoconus
•IOPcc-g and IOPcc/g
• IOPcc = IOPg + Corneal factor
⇒ Corneal factor = IOPcc - IOPg
• If IOPcc-g or IOPcc/g is high, there is corneal biomechanical change
more than normal condition.
• GAT can be underestimated in keratoconus.
Correlation Analysis with ORB Scan
• CH-CRF, CH/CRF
• CCT w as negatively correlated
• As w ell as CCT, simK value and irregular astigmatism of 3mm and 5mm
were also positively correlated.
• IOPcc-g, IOPcc/g
• Only CCT w as negatively correlated
Discussion
About keratoconus suspect
• Possibility to detect early keratoconus change or progression.
Limitations
• Cross-sectional study
• Difficult to generalize into the change in subject
Suggestions for future studies
• Study to find the risk factors of post-LASIK ectasia with various ORA
parameters.
Conclusions
The corneal biomechanical parameters and their combined
parameters measured using Ocular Response Analyzer were
correlated with topographic parameters.
So there is a possibility to put the biomechanical parameters to
practical use in detecting and monitor keratoconus.