Transcript Corneal Hysteresis and Corneal Resistance Factor in normal

OUTCOME OF REFRACTIVE SURGERY IN
KERATOCONUS SUSPECT EYES
Alain Saad MD, Damien Gatinel MD, PhD,
Anterior Segment and Refractive Surgery Department,
Center for Expertise and Research in Optics for Clinicians (CEROC)
Rothschild Foundation, Paris, France
The authors have no financial interest in the subject matter of this
poster.
World Cornea Congress, Boston, 7-9 April 2010
INTRODUCTION
?
Ectasia
The majority of post LASIK/PRK ectasia are observed in corneas sharing
topographical similarity to forme fruste keratoconus
However it’s not known whether
ectasia after LASIK or PRK
every suspicious cornea would undergo
PURPOSE
To describe retrospectively the results
of LASIK and PRK done inadvertently
in keratoconus suspect eyes.
METHODS
• We reviewed 1278 eye’s charts of patients that all
received refractive surgery performed by the same
surgeon (DG).
• The technique / indications were decided based on
clinical context and surgeon’s maps interpretation of:
– Orbscan ®
– OPDscan ® Placido analysis (no Corneal Navigator -CNincluded in the OPD station software at the time of surgery)
– Ocular Response Analyzer (ORA) data (Corneal Hysteresis
(CH) and Corneal Resistance Factor (CRF))
• We selected eyes diagnosed as Keratoconus suspect (KCS)
or Keratoconus (KC) by the CN (lately added to our OPD
station.
The Nidek Corneal Navigator uses an artificial intelligence technique to recognize
specific classifications of corneal topography. It calculates various indices
representing corneal shape characteristics and it give for each condition a
percentage of similarity ranging from 0 to 99%.
This software was not available at the time of the surgery but was added later on
our OPD machine.
13 EYES Classified KCS By THE NCN
OPD SCAN TOPOGRAPH
RESULTS
MSE CCT Age
CH
%
Post
Central CRF Similarity CH-CRF Elevation Thinnest
9.5
12
1
-5
532
27
88.7
-2.5
33.5
12
2
-6
570
38 12.0 11.3
36
0.68
25.5
4
3
4
5
6
7
8
9
10
-5.75
-7
-5.25
-7.5
-2
-2.75
-5.5
-2.75
560
545
554
560
541
601
508
524
38
23
49
49
28
27
28
41
11.8
10
9.9
11.1
NA
11.1
7.4
12.9
49.40
45.7
9.4
49.9
65
54.1
74.9
35.1
-0.3
0.15
-0.3
0.33
NA
0.9
0.8
0.2
21.00
20
23.1
31
26
15
15
20
8
3
6
11
13
5
6
9
11 -2.75 520
41 14.2 13.5
28.9
0.67
19
7
12 -3.75 505
13 -3.5 512
33 13.2 13
33 12.7 13.1
37.5
68.2
0.2
-0.4
21
25
11
12
11.5
10.1
9.6
11.4
NA
12
8.2
13.1
• 8 eyes had LASIK and 5 had PRK
• At 3 years of follow up: 100% +/- 0.50D intended correction
• No
topographical sign of ectasia
Mean Age (y):
32.6+/- 8.4
Mean Spherical
Equivalent = -4.5 +/- 1.7 D
M CCT=
541 +/- 28 microns
% similarity KCS (OPD):
49.4 +/- 21.1 %
RESULTS
Case examples : 5 and 6 :
Refraction: OD: -4.25 (-2.00 x 125)
OS: -7.50
Pre Lasik
Post Lasik
Refraction
OD: plano -0.50 x 115
OS: -1.25 -0.50 x 150
DISCUSSION
%
MSE CCT Age CH CRF Similarity CH-CRF Post Elevation
1
-5
532 27
9.5
12
2
-6 570 38 12.0 11.3
Parameter
4
3 -5.75 560 38 11.5 11.8
Topography
FFKC
4 -7
545 23 10.1 10
Pattern
5 -5.25 554 49
6
7
9.6
9.9
-7.5
560 49 11.4
11.1
RSB thickness
<240
-2
541 28
8 -2.75
Age 601 27
-2.5
33.5
ECTASIA
Points
88.7
36
3
0.68
49.40
-0.3
Inferior steepening/
45.7
0.15
SRA
12 11.1
9
-5.5 508 28 8.2 7.4
CT
<450
10 -2.75 524 41 13.1 12.9
MRSE
>-14
11 -2.75 520 41 14.2 13.5
12
RISK SCORE
25.5
2
21.00
ABT
Normal
LASIK
LASIK
4
LASIK
13
5
LASIK
5 >30
4
LASIK
6
7
PRK
1
PRK
1
PRK
5
PRK
1
PRK
31
260-279
280-299 11 >300
26
-0.4
3
1
0.33
68.2
LASIK
6
15
22-25
15
481-510
20
-10 to -12
19
26-29
>510
9
-8 to -10
-8 or less
7
J. Bradley Randleman,MD,Maria Woodward, MD, Michael J. Lynn, MS, R. Doyle
Stulting, MD, PhD. Risk Assessment for Ectasia after Corneal Refractive Surgery.
12 -3.75
505 33 13.2
37.5
0.2
21
11
Ophthalmology
2008; 13
115:37–50
13 -3.5 512 33 12.7 13.1
3
LASIK
49.9
240-259
74.9
0.8
451-480
35.1
0.2
-12 to -14
28.9
0.67
8
0
LASIK
4
23.1
0.9
4
2
3
-0.3
54.1
18-21
1
ECTASIA RISK
SCORE
Surgery
20
9.4
65
Central - Thinnest
25
12
Binder reviewed 1702 eyes with normal topographies and found that 19.6 % had an Ectasia Risk Score
of 3 or higher without any eye developing ectasia. The author conclude that this scoring system should
not be used to eliminate potential LASIK candidates with normal topography.
We reviewed eyes with abnormal topographies. Their mean Ectasia Risk Score was 3.1 +/- 1.9. 6 eyes
got Lasik with an Ectasia Risk Score ≥ 3 without any of them developing ectasia.
Thus other risk factors or protective element s for developing or not post Lasik ectasia are still unknown.
Perry S. Binder, MS, MD; William B. Trattler, MD. Evaluation of a Risk Factor Scoring System for Corneal Ectasia After LASIK. J. Refract.
Surg. 2010. In Press
DISCUSSION
The diagnosis of preoperative KCS condition was made objectively, based on the
Nidek Corneal Navigator System.
It’s specificity is less than 100%  Surgery could have been made on
« false positive for KCS » patients?
• In the first paper describing keratectasia, Seiler stated that « refractive
surgery reduces the biomechanical strength of the cornea which may
lead to mechanical instability and keratectasia »
• Binder studied more than 9000 eyes having at least one of the known risk factor
for ectasia without any of them developing this complication. He asked: « WHAT
IF ALL OF THE REPORTED ECTASIA CASES HAD A SINGLE AS YET UNDEFINED
UNDERLYING CONDITION THAT PREDISPOSED THE EYE TO DEVELOPPING
ECTASIA? »
•  Corneal biomechanics : determining the outcome ?
1)Seiler T, Koufala K, Richter G. Iatrogenic keratectasia after laser in situ keratomileusis. J Refract Surg 1998; 14:312–317
2)Perry S. Binder, MD. Analysis of ectasia after laser in situ keratomileusis: Risk factors. J. Cataract Refract Surg 2007; 33:1530–1538
DISCUSSION
Biomechanical properties
16.00
14.00
12.00
10.00
CH
8.00
OCULAR RESPONSE
ANALYSER
CRF
6.00
4.00
2.00
0.00
1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61
CH and CRF of a non operated KCS
population
Vs
CH and CRF of the 13 eyes
WE COMPARED CH AND CRF OF OPERATED EYES TO A POPULATION OF KCS
CORNEAS THAT WERE REJECTED FOR SURGERY
CH
(mmHg)
CRF
(mmHg)
OPERATED EYES
KCS SUSPECT GROUP
p
11.5 +/- 1.8
9.8 +/- 1.6
0.002941
11.4 +/- 1.7
9.4 +/- 1.6
0.000800
The Biomechanical properties
of the operated eyes were
significantly higher than those
of a non operated KCS group
CONCLUSION
1) WE HAVE INADVERTENTLY PERFORMED LASIK AND PRK ON PATIENTS
WITH KERATOCONUS SUPECT PLACIDO SIMILARITY.
2) THEY COULD BE FALSE POSITIVE FOR KCS?
3) WE DO NOT HAVE ECTATIC OUTCOME……………………………………
YET ?
4) CORNEAL BIOMECHANICS MAY INFLUENCE THE OUTCOME.
5) UNDEFINED UNDERLYING CONDITIONS THAT MAY PREDISPOSE
THE EYE TO DEVELOPPING ECTASIA ARE STILL TO INVESTIGATE.