Transcript Slide 1

Comparison of Central Corneal Thickness and
Peripheral Corneal Thickness using Sheimpflug system,
Optical Coherence Tomography and Ultrasound
Pachymetry in Normal, Keratoconus and Post-Refractive
Surgery Eyes at Different Corneal Thickness.
Ricardo N. Sepulveda, MD
Claudia Maria Prospero Ponce, MS
Karolinne Maia Rocha, MD PhD
William J. Dupps, MD PhD
Ronald R. Krueger, MD
Cole Eye Institute
Cleveland, OH
*Authors have no financial interest.
Background
Purpose: To compare central corneal thickness (CCT) and
peripheral corneal thickness (PCT) with scheimpflug system
(Pentacam), high-speed optical coherence tomography
(Visante) and ultrasound pachymetry (US) in normal eyes,
keratoconus suspect and post-laser in situ keratomileusis
(LASIK).
Setting: Department of Refractive Surgery, Cole Eye
Institute, The Cleveland Clinic. Cleveland, Ohio, USA.
Study Type: Retrospective Analysis
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Introduction
• Ultrasound pachymetry is currently the gold standard
in measuring CCT.
• Measurements taken with Pentacam and Visante-OCT
have demonstrated to be comparable to US.
• To our knowledge, this is the first study comparing
central pachymetry between the 3 systems in pre- and
post-LASIK eyes, and keratoconus suspects.
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Patients and Methods
• The CCT and PCT were measured with Pentacam (Oculus
Inc, Lynnwood, WA, USA) , US (Sonogage, Corneo-Gage
Plus, Sonogage Inc., USA) and Visante OCT(Carl Zeiss
Meditec Inc., Dublin, CA, USA,) in 163 eyes of 83 patients.
• 3 groups were retrospectively analyzed: Keratoconus
suspects, Post-LASIK and Normal patients (without Corneal
pathology).
• Keratoconus suspects were identified by the RabinowitzMacdonald criteria and using the PathFinder II Corneal
Analysis Software for the ATLAS™ Corneal Topography
System (Model 9000).
• Influence of age and corneal thickness was evaluated in all
groups, categorizing eyes with thin (≤500µm), normal (501550µm) or thick (≥551µm) corneas using US values.
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Patients and Methods
• Data was collected at 0 mm and 6 mm from Pentacam, 0-2mm
and 5-7mm from OCT, and a single value was obtained from
US.
• Multivariate generalized estimating equations were used to
analyze the correlations between the 3 measurements
obtained from the patients’ both eyes.
• Mean CCT and mean PCT difference between devices were
obtained for each group using multivariate linear regression.
• Analyzed factors included age, keratoconus suspects and
previous refractive surgery (LASIK); subsequently, influence of
absolute corneal thickness in pachymetry measurements was
determined.
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Results
• 83 patients (163 eyes)
• Mean age: 39 years (range 22-69 yrs.)
• 53 female, 30 male
• 40 eyes were keratoconus suspects, 17 post LASIK and 103
normal eyes.
• Mean spherical equivalent (SE) and Keratometry (Km) are
shown in Table 1.
• Keratometry readings ranged from 36.2 D to 59.5 D.
• Mean CCT for each group is shown in Table 2.
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Results
• CCT measurements were higher in US compared with
Pentacam (6.49 ±1.84μ; p<0.0005) and Visante OCT
(7.48+1.38μ; p<0.0005) for keratoconus suspects, post
LASIK and normal eyes, regardless of age and corneal
thickness.
• The greatest difference in mean CCT measurements was
observed in the post-LASIK group (Table 3), where
Pentacam measured thinner CCT than US and OCT.
• Peripheral corneal thickness measurements were superior
in Pentacam than in OCT(603.26± 38.83μ vs.
570.61±40.39μ; p<0.0005).
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Results
All
Normal
Keratoconus
Post Lasik
SE
-3.78 ± 3.36
-4.17 ± 3.03
-4.09 ± 3.75
-0.78 ± 2.29
Km
44.77 ± 2.14
44.63± 1.31
46.04 ± 2.6
42.2 ± 2.4
Table 1. Spherical equivalent and Km for all the eyes and for each individual group
Mean
CCT (value + SD)
US
Pentacam
OCT
PCT (value + SD)
Pentacam
OCT
Normal
Keratoconus
Post LASIK
523±28.04
516.28±31.6
515.41±29.1
6
523.02±41.61
513.57±43.96
512.67±42.3
1
526.06±66.73
501.66±73.74
516.35±66.14
597.37±34.20
564.26±34.8
575.05±45.28
608.97±42.79
628.82±46.91
600±49.79
Table 2. Mean central(CCT) and peripheral(PCT) corneal thickness with standard deviation in the 3 groups.
Mean Difference
CCT (value + SD)
Constant
Keratoconus
Post LASIK
US vs. Pentacam
P value*
US vs OCT
P
value*
Pentacam vs OCT
P value*
6.49±1.84
4.07± 3.34
17.75±4.86
0.0005
0.224
0.0005
7.48±1.38
3.28±2.51
2.04± 3.63
0.0005
0.190
0.575
0.89±1.39
0.21±2.58
15.61±3.66
0.521
0.935
0.0005
Table 3. Mean central corneal thickness difference between Ultrasound, Pentacam and Visante OCT
pachymetries in a paired analysis. Standard deviation is also shown.
*P value <0.05 was statistically significant
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Results
Mean Difference
PCT (value + SD)
Constant
Keratoconus
Post LASIK
Pentacam vs
OCT
P
value*
1.2±5.05
4.49±7.14
33.16±2.71
0.0005
0.812
0.53
Table 4. Peripheral corneal thickness was higher in Pentacam than in Visante OCT
(constant). No influence was observed in Keratoconus or Post LASIK patients.
*P value was statistically significant if <0.05
Mean Difference
CCT (value + SD)
Thick*
Thin**
Constant
US vs
Pentacam
P value*
US vs OCT
P
Value*
Pentacam vs
OCT
P
Value*
6.26±3.67
1.93±3.22
7.66±2.07
0.089
0.550
0.0005
3.6±2.64
-2.13±2.32
8.23±1.47
0.173
0.359
0.0005
-2.08±3.02
-4.44±2.67
0.68±1.64
0.491
0.096
0.679
Table 5. US gives thicker measurements than OCT and Pentacam(p<0.0005).
The difference between US and Pentacam were similar at any absolute corneal
thickness.
*>551µm
*≤500µm
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Results
Figure 1. Linear regression plots showing the correlation between US/Pentacam, US/Visante OCT, and
Pentacam/Visante OCT respectively in Keratoconus Suspect eyes. A linear correlation can be
illustrated with the 3 methods.
Figure 3. Linear regression plots showing the correlation between US/Pentacam, US/Visante OCT, and
Pentacam/Visante OCT in normal eyes.
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Results
Figure 4. Peripheral corneal
thickness correlation between
Pentacam and Visante OCT.
Pentacam values were constantly
higher than OCT.
Figure 5. Peripheral pachymetries
in post LASIK eyes. Correlation
between Pentacam and Visante
OCT.
Figure 6. Correlation between
peripheral pachymetries in eyes
unoperated and without disease.
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Conclusion
• These recently new devices do not replace US pachymetry but
rather complement each other in the preoperative evaluation of
refractive surgery candidates, aid in the diagnosis and treatment
of keratoconus suspects, help evaluate the lens, screen for
glaucoma and allow room for more research in all ophthalmologic
fields.
• Ophthalmologists should be familiar with the difference in CCT
between US, Pentacam and Visante OCT.
• Pentacam and Visante OCT can be used interchangeably for
central pachymetry, however, in post LASIK patients, Visante
OCT might perform better pachymetry maps than Pentacam.
• Further studies are suggested in order to establish the influence
of age in peripheral pachymetry.
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