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Abstract
Purpose
To compare corneal pachymetry assessment using four measurement methods in normal and post-femtosecond laser-assisted LASIK eyes.
Methods
Central corneal thickness was measured sequentially using Orbscan II, Pentacam, Galilei and ultrasonic pachymetry in 30 normal, non-surgical eyes (Group I), 30 eyes one to six months after femtosecond laser-assisted LASIK (Group II), and 30 eyes six months or longer after femtosecond laser-assisted LASIK (Group III).
Results
In Group I, corneal thickness measurements were similar for all four methods (P=0.202, one way ANOVA). In Groups II and III, corneal thickness measurements were significantly different (P=0.000, respectively, one way ANOVA). Compared to the Pentacam, Galilei and ultrasonic pachymetry, Orbscan significantly underestimated the corneal thicknesses in Groups II and III (P＜0.005, respectively, one way ANOVA).
Conclusions
Central corneal thicknesses of normal eyes were similar for all four measurements, therefore corneal thickness measurements before refractive surgery using all four measurements is suitable. However measurements obtained with the Orbscan II were thinner than those obtained with the Pentacam, Galilei or ultrasonic pachymetry in post femtosecond laser-assisted LASIK eyes. Further studies are needed to determine which instrument is more accurate in measuring central corneal thickness before and after refractive surgery.
References
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Figure 1.
Mean and 95% CI of CCT measurement by Orbscan, Pentacam, Galilei and US in Group I (CI=confidence interval; CCT=central.thickness; US=Ultrasonic pachymetry).
Figure 2.
Mean and 95% CI of CCT Measurement by Orbscan, Pentacam, Galilei and US in Group II (CI= confidence interval; CCT=central. thickness; US= Ultrasonic pachymetry).
Figure 3.
Mean and 95% CI of CCT Measurement by Orbscan, Pentacam, Galilei and US in Group III. (CI= confidence interval; CCT=central. thickness; US=Ultrasonic pachymetry).
Figure 4.
Bland-Altman plots of Galilei, Pentacam and Orbscan CCT readings against US measurement in Group I. The middle line is the mean and the lines on the side represent the upper and lower 95% limits of agreement (LoA).
Figure 5.
Bland-Altman plots of Galilei, Pentacam and Orbscan CCT readings against US measurement in Group II. The middle line is the mean and the lines on the side represent the upper and lower 95% limits of agreement (LoA).
Figure 6.
Bland-Altman plots of Galilei, Pentacam and Orbscan CCT readings against US measurement in Group III. The middle line is the mean and the lines on the side represent the upper and lower 95% limits of agreement (LoA).
Table 1.
Characteristics of the study groups
| Group I† | Group II‡ | Group III§ | |
|---|---|---|---|
| Patients (eyes) | 30 | 30 | 30 |
| Sex (M:F) | 5:10 | 2:13 | 2:13 |
| Age (mean) | 27.45±7.49 | 29.33±7.49 | 25.92±4.25 |
| Manifest refractive error (SE) (D)* | –4.50±1.72 | –4.25±1.65 | –4.19±1.61 |
| SE Correction (D)* | –4.64±1.70 | –4.51±1.64 | |
| Follow-up duration (Month) | 5.80±4.33 | 11.23±7.26 |
Table 2.
Corneal thickness measurements in normal and post-femtosecond laser-assisted LASIK eyes using orbscan II, pentacam, galilei and ultrasound pachymetry (Mean± SE, μm)
| Group | Orbscan | Pentacam | Galilei | US* | P value |
|---|---|---|---|---|---|
| I† | 535.8±40.7∏ | 544.5±30.7 | 554.2±30.4 | 541.8±31.3 | 0.202 |
| II‡ | 440.3±40.3∏ | 478.8±28.6 | 488.0±30.1 | 474.7±32.1 | .000＃ |
| III§ | 432.2±51.7∏ | 472.5±33.5 | 482.8±32.9 | 470.0±33.3 | .000＃ |
Table 3.
Mean difference, limit of agreements and pearson correlation in corneal thickness measurements for galilei, pentacam, orbscan and ultrasound pachymetry in group I, II and III
| Group and measurement | Mean difference (μm) | 95% Limit of agreements (μm) | P Value | Pearson correlation (R)(p<.001) |
|---|---|---|---|---|
| Group I† | ||||
| Galilei-US* | 12.3 | –10.2, 34.9 | 0.487 | 0.982 |
| Pentacam-US* | 2.7 | –19.9, 25.3 | 0.989 | 0.984 |
| Orbscan-US* | –6.1∏ | –28.6, 16.5∏ | 0.897 | 0.932 |
| Group II‡ | ||||
| Galilei-US* | 13.2 | –9.0, 35.5 | 0.412 | 0.983 |
| Pentacam-US* | 4.1 | –18.2, 26.4 | 0.964 | 0.980 |
| Orbscan-US* | –34.4∏ | –56.7, −12.1∏ | 0.001＃ | 0.903 |
| Group III§ | ||||
| Galilei-US* | 12.8 | –13.2, 38.9 | 0.573 | 0.972 |
| Pentacam-US* | 2.4 | –23.6, 28.5 | 0.995 | 0.977 |
| Orbscan-US* | –37.8∏ | –63.8, −11.7∏ | 0.001＃ | 0.918 |
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