1. Comparison of Central Corneal Thickness measured by
Four methods in normal
and Post-IntraLASIK eyes
Hyun Ju Lee, M.D., Suk Kyue Choi, M.D.,
Do Hyung Lee, M.D., Ph.D., Jin Hyoung Kim, M.D.
Department of Ophthalmology, Ilsan Paik Hospital, Inje University College of Medicine, Gyeonggi, Korea
Authors have no financial interest

2. PURPOSE using four measurement methods in normal eyes
To compare corneal pachymetry assessment
using four measurement methods in normal eyes
and Post-IntraLASIK eyes

3. METHODS Corneal pachymetry assessment using 1. Ultrasonic pachymetry
(Advent, Mentor O&O, Norwell, MA, USA )
- Default velocity : 1641 (m/s)
2. Scanning slit topography
(Orbscan II; Bausch & Lomb, Rochester,NY)
- Acoustic equivalent correction factor : 0.95
3. Rotating Scheimpflug Camera
(Pentacam; Oculus Inc, Wetzlar, Germany)
4. Dual Scheimpflug Analyzer
(GALILEI™; Ziemer)

4. METHODS Group I - 30 unoperated eyes (Unoperated group) Group II
- 30 eyes : shorter than 6 months after IntraLASIK
(Early postoperative IntraLASIK group)
Group III
- 30 eyes : longer than 7months after IntraLASIK
(Late postoperative IntraLASIK group)

5. Corneal Thickness Measurement
RESULTS
Corneal Thickness Measurement I
440±40.3
.000
Group
535±40.7
432±51.7
541±31.3
475±32.1
470±33.3
544±30.7
479±28.6
472±33.3
554±30.3
488±30.1
483±32.9
0.202
Mean±SD (um)
Galilei
Pentacam
Ultrasound
Orbscan
P Value II
III
One-Way ANOVA
Group I, the four measurements were similar with a mean difference
within 18.4 μm. (P=.202)
Group II & III, Orbscan were thinner than other mesurements. (P=.000)

6. RESULTS Corneal Thickness Measurement
Group and Measurement
-12.3
Mean differnece
(um)
95% Limit of
Agreement
P Value
Pearson Correlation
(R) (p < 0.001)
U - G
-34.9, 10.2
0.487
0.982
-2.7
-25.3, 19.9
0.989
0.984
6.1
-16.51, 28.62
0.897
0.932
-13.2
-35.5, 9.0
0.412
0.983
-4.1
-26.4, 18.2
0.964
0.980
34.4
12.1, 56.7
0.001
0.903
-12.8
-38.9, 13.2
0.573
0.972
-2.4
-28.5, 23.6
0.995
0.977
37.8
11.7, 63.8
0.918
U - P
U - O
Group I II
III
G = Galilei, P = Pentacam, U = Ultrasound, O = Orbscan II
ANOVA, Scheffe multiple comparison test
Group II & III, Compared to the ultrasound measurement, orbscan
significantly underestimated the corneal thickness. (P=.001)

7. Corneal Thickness Measurement
RESULTS
Corneal Thickness Measurement
Group and Measurement
-28.4
Mean differnece
(um)
95% Limit of
Agreement
P Value
I - II
-41.2,-15.5
.000
-31.7
-44.6, 18.8
I - III
Group
U - O
-3.3
-16.2, 9.5
0.812
II - III .
U = Ultrasound, O = Orbscan II
ANOVA, Scheffe multiple comparison test

8. Bland-Altman plots comparing the 4 modalities (Group I)
Group I, all four methods showed good agreement, with a mean difference
being within ± 20 um.

9. Bland-Altman plots comparing the 4 modalities (Group II)
Group II, galilei and pentacam showed good agreement with ultrasound, with
a mean difference being within ± 10 um.
Group II, the limits of agreement between orbsan and ultrasound were 0.5 um
and – 69.3 um with a range of 69.8 um.

10. Bland-Altman plots comparing the 4 modalities (Group III)
Group III, galilei and pentacam showed good agreement with ultrasound,
with a mean difference being within ± 10 um.
Group III, the limits of agreement between orbsan and ultrasound were 11.1 um
and – 86.5 um with a range of 97.6 um.

11. RESULTS Group I (CCT) - Similar for all four methods (P=.202)
Group II, III (CCT)
- No statistically significant difference among Galilei,
Pentacam and Ultrasound
- Orbscan measurements were thinner than other
mesurements
After IntraLASIK, Galilei & Pentacam was comparable to Ultrasound(current gold standard for corneal pachymetry)
Orbscan measurement of CCT after refractive surgery are less than those measured by US

12. DISCUSSION
CCT using Galilei and Pentacam before and after IntraLASIK is also suitable
CCT using orbscan tends to be underestimated compared with other values after refractive surgery (Group II & III )
Further studies are needed to determined which instrument is more accurate in measuring CCT