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From Geometrical and Optical understanding, the next step is biological evaluation: healing response and biomechanics Ectasia mysteries* in Refractive Surgery had
highlight the need for corneal biomechanical understanding(*ie: cases with no risk factors that develop ectasia after LASIK) Also to Customize Refractive Corneal
Treatments; correctly measure IOP (intraocular pressure) and to possibly predict glaucoma risk Corneal biomechanical evaluations were limited
to in vitro studies and to mathematical finite element models until the Ocular Response Analyzer (ORA-Reichert, Depew) in 2005 New techniques are under development for
evaluating biomechanics This e-Poster presents a new system – The
Corvis ST (Oculus, Wetzlar, Germany) with preliminary clinical results.
Ultra High-Speed (UHS ST) Scheimpflug Technology takes 4,330 frames/sec with 8mm horizontal coverage Monitors corneal deformation response to
a symmetrically metered air pulse
The Oculus Corvis ST
1. Natural; (Ingoing Phase) 2. First Applanation (1st A) Momentum; 3 and 4. Ingoing Concavity Phase; 5. Highest Concavity Momentum; 6. Oscillation Period; (Outgoing Phase); 7. Second Applanation (2nd A) Momentum; 8.
After Second Applanation; 9. Natural Back1st Applanation, Highest Concavity and 2nd Applanation: Time and Length; Maximum Deformation; Maximum Velocity In and Out; Thickness
Corvis ST: First Studies Experiment involving contact lenses mounted on
an artifical pressurized chamber (Caldas et al., ePoster ASCRS 2011) found that the deformation response is influenced by lens properties and chamber pressure. The inspection of the actual deformation process
details corneal characterization, which has a potential for distinguishing normal (A, B) and keratoconus (C, D) corneas (see video* (see video* PosterASCRS2011_clip_RAmbrosio).PosterASCRS2011_clip_RAmbrosio).
Natural and Highest Deformation Momentum in a Normal (A, B) and a Keratoconic (C, D) Cornea
1st A Length(max):1st A Time:2nd A Length(max):2nd A Time:Curv, Rad, HC:Def,Amp,(max):
The Corvis ST was utilized to assess corneal deformation response in one eye from 71 keratoconic patients and in one eye from 178 normal patients. Clinical diagnosis was based on the complete eye
exam, Placido-disk based corneal topography and Pentacam Corneal Tomography.
Clinical Study
Wilcoon Rank Sum (Mann- Whitney Test)
IOP: < 0.00011st A Time: < 0.00012nd A Time: 0.0006
1st A Length(max): 0.00372nd A Length(max): 0.0008Curv. Rad. Normal: 0.4126
Curv. Rad. HC: < 0.0001Pachy Apex: < 0.0001
W-Dist.: 0.0191Def.Amp.(max): < 0.0001
Vin: < 0.0001Vout: 0.0001
Statistically significant distributions for all parameters (Mann-Whitney, p<0.05), but with significant overlap and AUC(area under the ROC curves) between 0.673 and 0.852
Joint work with “Instituto de Computação” at UFAL (Universidade Federal de Alagoas*) to develop a combined parameter (Corvis Combo1) based on a linear regression analysis, considering the effects of IOP on deformation response parameters 0.033 * IOP - 0.004 * Pachy Apex - 0.448 * 1st A Time - 0.049 * HC Time + 0.093 * 2nd A Time + 0.026 * 1st A Length(max) - 0.105 * 2nd A Length(max) + 0.208 * Def Amp (max) - 0.619 * W-Dist - 0.021 * Curv, Rad, HC - 0.101 * Curv, Rad, Normal - 0.525 * Vin - 0.166 *
1st A Time:Def,Amp,(max):Pachy Apex:Curv, Rad, HC:Curv, Rad, Normal:combo1
AUC SE a 95% CI b 1st_A_Time_ 0,802 0,0313 0,747 to 0,850
Def_Amp__max__ 0,749 0,0355 0,691 to 0,802Pachy_Apex_ 0,852 0,0265 0,801 to 0,893
Curv__Rad__HC_ 0,852 0,0290 0,802 to 0,894Curv__Rad__Norm
al_ 0,810 0,0329 0,755 to 0,857CorvisST Combo1 0,931 0,0191 0,892 to 0,959
a DeLong et al., 1988 b Binomial exact
The Corvis ST Combo1 performed statistically better (p<0.05; Pairwise ROC comparisons) than the individual parameters from the Corvis ST to distinguish 71 keratoconic eyes and 178 normal eyes (one eye per patient included) This approach has been complementary to
enhance the diagnosis of ectasia susceptibility.
Clinical Study
0 20 40 60 80 100
0
20
40
60
80
100
100-Specificity
Sen
sitiv
ity
1st A Time:Def,Amp,(max):Pachy Apex:Curv, Rad, HC:Curv, Rad, Normal:combo1
There were very significant correlations (Spearman, p<0.001) between IOP and 1st Applanation Time (rho=0.94), 2nd Applanation Time (rho=-0.73), Deformation Amplitude (rho=-0.80), W-Dist (rho=-0.66), Curv Rad HC (rho=0.45), Vin (rho=-0.49), Vout (0.38) and Combo1 (rho=-0.44)There were significant correlations (Spearman, p<0.01)
between Pachymetry at the Apex and IOP (rho=0.37), 1st Applanation Time (rho=0.4) and Lengh (rho=-0.18 ), W-Dist (rho=-0.25), Curv Rad HC (rho=0.48), Vout (rho=0.3), and Combo1 (rho=-0.64) There was a positive correlation between age and HC
Biomechanical data from Corvis ST enhances the Biomechanical data from Corvis ST enhances the capability to detect very mild cases of ectasia and also capability to detect very mild cases of ectasia and also help to characterize stable cases with asymmetric bow tie help to characterize stable cases with asymmetric bow tie and inferior steepening (ABT/IS).and inferior steepening (ABT/IS). 26 eyes diagnosed as Forme Fruste Keratoconus 26 eyes diagnosed as Forme Fruste Keratoconus
(FFKC), with normal front curvature map while the fellow (FFKC), with normal front curvature map while the fellow eye has keratoconus were examined.eye has keratoconus were examined. 25 eyes with ABT/IS but with no other clinical or 25 eyes with ABT/IS but with no other clinical or
tomographic sign of ectasia were examined. tomographic sign of ectasia were examined. Combo1 24/178 (13%) normal eyes >0.21 9/71 (13%) keratoconic eyes <0.21 21/26 (80%) eyes with FFKC >0.21 8/25 (32%) ABT/IS cases >0.21
Kruskall-Wallis Test Normal KC FFKC ABT/IS
Normal <0.05 <0.05 NS
KC NS <0.05
FFKC <0.05
N FFK1 KC ABT
Ave
-0,0080
10,3455
290,5068
290,1337
45
SD0,2183
480,1960
430,2669
10,1816
24 171 26 71 25
see video* see video* PosterASCRS2011_clip_RAmbrosioPosterASCRS2011_clip_RAmbrosio
The inspection of corneal deformation during NCT enables biomechanical characterization The deformation is severely influenced by IOP Combo1 from Corvis ST provides clinically
relevant parameter to enhance sensitivity and specificity to detect ectasia.
Corvis ST: Conclusions
ABT with no Ectasia (A,B) x FFKC (C, D)
This approach This approach is is complementary complementary to Corneal to Corneal Tomography Tomography with the with the Pentacam for Pentacam for screening screening refractive refractive candidatescandidates