Transcript Document

Corneal Biomechanical
Changes Following Surface
Keratorefractive Surgery
Teeravee Hongyok, MD, Christopher J. Rapuano, MD,
Ajoy Virdi, MBBS, Elisabeth J. Cohen, MD,
Kristin M. Hammersmith, MD
Cornea Service, Wills Eye Institute
Jefferson Medical College, Thomas Jefferson University
Philadelphia, PA
The authors have no financial interest in the subject matter for this poster.
World Cornea Congress VI, Boston, MA, USA, April 7-9, 2010
Ocular Response Analyzer
(ORA)
• The ORA is the only machine that can perform direct
clinical assessment of corneal biomechanical properties.
• 4 main parameters are measured by ORA:
• Corneal Hysteresis (CH) is the difference in inward and outward applanation
pressures (P1 and P2). CH may reflect viscoelasticity of cornea.
• Corneal Resistance Factor (CRF) may reflect elasticity of cornea
• Goldmann Correlated IOP (IOPG)
• Corneal Compensated IOP (IOPCC)
• The signal peak height and multiple oscillations are changed in post-laser in situ
keratomileusis (LASIK) keratectasia eyes compared to the normal post-LASIK eye
(Glass DH, et al., ARVO 2008; E-abstract 646).
• Using the new ORA software (version 2.04) launched in 2009, the device can
mathematically describe the ORA waveform characteristics with 38 new
parameters including height, slope, area-under-the curve and waveform score.
Pictures from http://www.ocularresponseanalyzer.com/
Corneal Biomechanics in Keratoconus
and after Refractive Surgery
CH and CRF have been found to be significantly
reduced in patients with keratoconus1,2 and post-LASIK
corneal ectasia3
LASIK was also found to decrease CH and CRF.4-8
The significant alteration of corneal biomechanics may
play a critical role in development of this serious ectatic
complication after refractive surgery.
We hypothesized that surface ablation, which has no
stromal flap and leaves a thicker residual stromal bed,
would result in less change in corneal biomechanics than
LASIK.
1Luce
JCRS 2005, 2 Kirwan Ophthalmologica 2008, 3Kerautret JCRS 2008, 4 Pepose AJO
2006, 5Ortiz JCRS 2007, 6Chen JCRS 2008, 7Hamilton JCRS 2008, 8 Kirwan JCRS 2008
Purpose
To evaluate pre- and post-operative
changes in corneal biomechanical
properties
using the Reichert Ocular Response
Analyzer (ORA)
in patients who undergo surface
keratorefractive surgery.
Methods
Prospective, non-randomized clinical trial
Inclusion: patients over the age of 18 who planned to
undergo surface keratorefractive surgery on the Cornea
Service at Wills Eye Institute from November 2008 to
February 2009
IRB approved
Data collection: before surgery, 1 and 3 months after
surgery
– Corneal thickness: U/S (Accupach V) and optical (Galilei)
– Corneal topography: Atlas 995 (Carl-Zeiss) and Galilei (Ziemer)
– Reichert ORA hardware version 3.0, software version 2.04
Basic biomechanics parameters and new waveform
parameters were analyzed.
Results
9 eyes of 5 male patients underwent custom off-flap myopic
epi-LASIK and completed 3 month F/U (age: 36 ± 7.8 years).
Preoperative
Postoperative
1 month
3 months
UCVA [logMAR ± SD]
(Snellen)
1.20 ± 0.17
(20/316)
-0.01 ± 0.1
(20/20+)
-0.06 ± 0.05
(20/17)
MRSE (D)
-4.4 ± 1.25
+0.18 ± 0.31
-0.21 ± 0.36
Atlas
43.80 ± 0.44
40.07 ± 1.03
40.50 ± 0.99
Galilei
43.39 ± 0.44
39.64 ± 1.16
39.96 ± 1.08
Mean keratometry (mean ± SD, D)
Laser ablation depth (μm)
60.67 ± 17.2
Pachymetry (mean ± SD, μm)
U/S (Accupach V)
549 ± 31
467 ± 37
495 ± 27
Optical (Galilei)
560 ± 29
495 ± 32
503 ± 34
Corneal Biomechanics (mmHg)
Basic Corneal Biomechanics Parameters
Changes after Epi-LASIK
18
*
16
14
12
10
*
*
*
*
*
*
8
6
4
2
0
Preoperative
Postop. 1 month
Postop. 3 months
CH
CRF
IOPg
IOPcc
10.1
7.4
8.1
9.6
6.4
6.9
13.7
10.6
10.24
14.8
14.9
13.9
* P < 0.05
(Wilcoxon Signed Rank Test)
Corneal Hysteresis Changes after
Laser Refractive Surgery:
compared to other studies
0
CH Changes (mmHg)
-0.5
-1
-1.5
-2
-2.5
-3
-3.5
Mean Changes
No. of Eyes
LASIK
Pepose2007
LASIK
Ortiz2007
LASIK
Chen2008
LASIK
Kirwan2008
LASIK
FS-LASIK
PRK
Hamilton2008 Hamilton2008 Hamilton2008
-1.7
-1.1
-2.04
-1.9
-2.2
-1.9
66
65
43
90
32
32
LASEK
Kirwan2008
Epi-LASIK
Hongyok2009
-2.3
-2.2
-2
33
35
9
Corneal Resistance Factors Changes
after Laser Refractive Surgery:
compared to other studies
0
CRF Changes (mmHg)
-0.5
-1
-1.5
-2
-2.5
-3
-3.5
-4
-4.5
Mean Changes
No. of Eyes
Epi-LASIK
PRK
FS-LASIK
LASIK
Hamilton2008 Hamilton2008 Hamilton2008 Hongyok 2009
LASIK
Pepose2007
LASIK
Ortiz2007
LASIK
Chen2008
-2.8
-1.35
-3.21
-3.5
-3.5
-2.9
66
65
43
32
32
33
-2.7
9
New Waveform Parameters:
Significant Changes in 9 of 38 (p<0.05)
Decreased Peak 1
parameters
• Height of peak1
(H1)
• Height of peak1 at
50% applanation
peak (H11)
• Absolute value of
monotonic decrease
on downslope part
of peak1 starting at
the peak value
(Dive1)
• Area under the P1
curve (P1area)
•Decreased overall Waveform Score
Preoperative ORA signal
Postoperative ORA signal
Decreased Peak 2
parameters
• Upslope of peak2
(Uslope2)
• Maximum single
step increase in rise
of peak1 (Mslew2)
• Aspect ratio
(height/width) of peak
2 (Aspect2)
• Aspect ratio of
downslope
(height/width) (Slew2)
Sample of Signal Overlay of Preoperative ORA and Postoperative ORA
Conclusions
Epi-LASIK, a surface ablation procedure, significantly
reduced corneal hysteresis and corneal resistance factor.
Unexpectedly, the magnitude of reduction seems to be
similar to LASIK from previous publications.
– It appears that corneal thickness is more important
than the flap creation on the corneal biomechanics.
Waveform analysis also found significant changes in both
peak 1 and peak 2 and a decrease in overall waveform
score after surface ablation.
Conclusions
A marked decline in these parameters may
reflect changes in the viscous and elastic
qualities of the cornea after surface ablation.
Future work is needed to determine whether
differences in these corneal biomechanical
parameters are useful in detecting patients who
are at risk to develop post-refractive surgery
ectasia, even after surface ablation.