Comparison of central corneal thickness measurements in corneal edema using ultrasound pachymetry, Visante anterior-segment optical coherence tomography, Cirrus optical coherence tomography, and Pentacam Scheimpflug camera tomography

Figures & data

Table 1 Intraclass correlation coefficients of central corneal thickness measurements in normal subjects

Reproducibility	ICC (95% CI)*
	Pentacam	Ultrasound	Visante	Cirrus
Intraobserver
A1, A2	0.95 (0.88–0.98)	0.99 (0.97–0.99)	0.98 (0.96–0.99)	0.98 (0.95–0.99)
B1, B2	0.97 (0.91–0.99)	0.98 (0.95–0.99)	0.99 (0.97–0.99)	0.97 (0.93–0.99)
Interobserver
A1, B1	0.96 (0.91–0.99)	0.97 (0.92–0.99)	0.99 (0.96–0.99)	0.97 (0.93–0.99)
A2, B2	0.95 (0.86–0.98)	0.98 (0.93–0.99)	0.98 (0.95–0.99)	0.98 (0.95–0.99)

Notes:

* Two-way random model, absolute agreement, single measure. A1, first measurement by examiner 1; A2, second measurement by examiner 1; B1, first measurement by examiner 2; B2, second measurement by examiner 2.

Table 2 Repeated-measure analysis of variance with Bonferroni post hoc comparison, LOA, and ICC

Reproducibility of each device	Intraobserver A1, A2	Interobserver A1, B1
Pentacam
Difference: mean (SD)	28.4 (289.7)	41.8 (352.8)
95% CI	−64.3 to 121.0	−71.0 to 154.7
P-value	0.539	0.458
LOA	−539.4, 596.2	−649.7, 733.3
ICC (95% CI)	0.947 (0.903, 0.972)	0.926 (0.865, 0.960)
Ultrasound
Difference: mean (SD)	1.58 (4.99)	1.68 (15.98)
95% CI	−0.02 to 3.17	−3.43 to 6.78
P-value	0.053	0.511
LOA	−8.2, 11.4	−29.6, 33.0
ICC (95% CI)	0.999 (0.998, 0.999)	0.988 (0.978, 0.994)
Visante
Difference: mean (SD)	−2.20 (9.81)	1.35 (9.64)
95% CI	−5.34 to 0.94	−1.73 to 4.43
P-value	0.164	0.381
LOA	−21.4, 17.0	−17.6, 20.3
ICC (95% CI)	0.994 (0.989, 0.997)	0.994 (0.989, 0.997)
Cirrus
Difference: mean (SD)	−0.85 (6.48)	−0.50 (9.80)
95% CI	−2.92 to 1.22	−3.63 to 2.63
P-value	0.412	0.749
LOA	−13.6, 11.9	−19.7, 18.7
ICC (95% CI)	0.998 (0.9955, 0.999)	0.995 (0.990, 0.997)

Notes: The values are expressed in micrometers except for the ICC. A1, first measurement by examiner 1; A2, second measurement by examiner 1; B1, first measurement by examiner 2.

Abbreviations: ICC, intraclass correlation coefficient; LOA, limits of agreement.

Figure 1 Comparisons of central corneal thickness (CCT) measurement among the four devices.

Notes: (A) Pentacam and Cirrus optical coherence tomography (OCT); (B) Pentacam and ultrasound (US) pachymetry; (C) Pentacam and Visante OCT; (D) US and Cirrus OCT; (E) US and Visante OCT; (F) Visante OCT and Cirrus OCT. Corneal edema was graded 1–3, respectively, for CCTs <650 μm (circles), CCTs 650–850 μm (solid triangles), and CCTs exceeding 850 μm (triangles).

Figure 2 Bland–Altman plots showing agreement of central corneal thickness (CCT) measurements among the four devices.

Notes: (A) Pentacam and Cirrus optical coherence tomography (OCT); (B) Pentacam and ultrasound (US) pachymetry; (C) Pentacam and Visante OCT; (D) US and Cirrus OCT; (E) US and Visante OCT; (F) Visante OCT and Cirrus OCT. Mean difference between each pair of devices with 95% limits of agreement and mean difference ±1.96 SD are shown. The highest agreement of CCT measurements was between the Visante and Cirrus OCT devices.

Figure 3 Comparison of interobserver and intraobserver repeatability between two central corneal thickness (CCT) measurements from each of the four devices. Notes: Correlations between the two examinations by one examiner of CCT measurement by (A) the Pentacam, (B) Visante optical coherence tomography (OCT), (C) Cirrus OCT, and (D) ultrasound (US) pachymetry. Correlations between the two examiners of CCT measurement by (E) the Pentacam, (F) Visante OCT, (G) Cirrus OCT, and (H) US. A1, first measurement by examiner 1; A2, second measurement by examiner 1; B1, first measurement by examiner 2.

Table 3 Central corneal thickness measurements from each device compared by corneal thickness

Edema severity	Eyes, n	Mean ± SD
		Pentacam	Ultrasound	Visante	Cirrus
1	20	604.9±30.812	595.2±31.095	596.2±29.486	597.8±28.239
2	17	1,213.0±1,046.388	694.35±37.308	684.65±27.504	683.06±27.66
3	3	2,553.00±1,602.725	939.67±155.32	909.67±59.138	910.67±131.838

Table 4 Mean difference ± SD, LOA, ICCs, and correlations between the pairs of methods

Method 1	Method 2	Difference			LOA	ICC (95% CI)#	R
		Mean	95% CI	P-value*
Pentacam	Ultrasound	346.3	62.4–630.1	0.018	−1,393.4, 2,086.0	0.09 (−0.18 to 0.37)	0.46
Pentacam	Visante	352.1	69.3–635.0	0.016	−1,381.4, 2,085.7	0.09 (−0.18 to 0.37)	0.55
Pentacam	Cirrus	352.0	67.4–636.5	0.017	−1,392.0, 2,095.9	0.09 (−0.19 to 0.36)	0.48
Ultrasound	Visante	5.9	−4.4 to 16.2	0.256	−57.2, 69.0	0.95 (0.90–0.97)	0.96
Ultrasound	Cirrus	5.7	−2.5 to 13.8	0.168	−44.4, 55.7	0.97 (0.94–0.98)	0.97
Visante	Cirrus	−0.2	−6.5 to 6.1	0.949	−38.8, 38.4	0.98 (0.96–0.99)	0.98

Notes:

* Paired t-test;

# two-way random model, absolute agreement, single measure. Values are expressed in micrometers, except for correlations and ICCs.

Abbreviations: LOA, limits of agreement; ICCs, intraclass correlation coefficients.

Figure 4 Central corneal thickness measurements in each grade of corneal edema and anterior-segment photos obtained using the Pentacam with inexact anterior and posterior corneal alignment.

Notes: (A) Corneal alignment in patient one by Pentacam; (B) corneal alignment in patient four by Pentacam.