Daily Variations of Corneal White-to-White Diameter Measured with Different Methods

Figures & data

Figure 1 Possible reference points when determining diameters of the cornea and anterior chamber.

Table 1 Descriptive Data of the Average Values of Three WTW Corneal Diameter Measurements at Each Time Point Assessed in mm with Three Different Methods: Median (1st Quartile – 3rd Quartile), Mean ± Std. Deviation, n = 20

Device	Time of the Measurement			Quartile Coefficient of Dispersion, %	p-value Friedman
	8 a.m.	11 a.m.	2 p.m.
Pentacam HR	11.70 (11.48–12.00)	11.70 (11.40–11.93)	11.80 (11.38–12.03)	0.4 (0.3–2.1)	0.436
	11.74 ± 0.47	11.73 ± 0.48	11.78 ± 0.51
Keratograph 5M	11.79 (11.53–12.06)	11.72 (11.56–12.00)	11.69 (11.53–12.05)	0.3 (0.2–0.4)	0.607
	11.81 ± 0.35	11.81 ± 0.35	11.80 ± 0.38
Slitlamp	12.02 (11.57–12.44)	11.83 (11.44–12.01)	11.92 (11.62–12.18)	2.1 (1.3–2.6)	0.247
	11.97 ± 0.59	11.80 ± 0.51	11.83 ± 0.56
Quartile coefficient of dispersion, %	1.8 (1.3–2.1)	1.0 (0.5–1.7)	1.4 (1.1–2.2)
p-value Friedman	0.041*	0.106	0.382

Notes: *Statistical significance Pentacam HR vs slitlamp: p = 0.024 (Wilcoxon signed rank test corrected acc. Holm-Bonferroni). Even if not all the samples seem to be normally distributed (Figure 2), mean and std. deviation are shown in order to compare with the data by other authors.

Abbreviation: WTW, white-to-white.

Figure 2 Boxplots for the horizontal white-to-white corneal diameter values measured with the three different methods at the three different measuring times (n = 20).

Figure 3 Bland Altman plots to describe the agreement between the measurements with the different devices (n = 20): (A) between slitlamp and Pentacam HR; (B) between slitlamp and Keratograph 5M; (C) between Pentacam HR and Keratograph 5M.

Table 2 Repeatability of the Three Measurement Methods Described by the Non-Parametric Coefficient of Variation, QCD and the Intra-Class Correlation Coefficient (ICC): Median (1st Quartile – 3rd Quartile) for QCD and Mean (95% CI) for ICC, n = 20. Three Measurements Were Performed at Each Time Point with Each Device. Their Average Values are Shown in Table 1

Device	Parameter	Time of the Measurement			p-value Friedman: QCD
		8 a.m.	11 a.m.	2 p.m.
Pentacam HR	QCD, %	0.0 (0.0–0.0)	0.0 (0.0–0.3)	0.0 (0.0–0.1)	0.891
	ICC	0.977 (0.945–0.992)	0.995 (0.989–0.998)	0.990 (0.973–0.997)
Keratograph 5M	QCD, %	0.3 (0.2–0.4)	0.3 (0.2–1.0)	0.4 (0.2–0.5)	0.323
	ICC	0.971 (0.930–0.990)	0.668 (0.384–0.865)	0.944 (0.861–0.982)
Slitlamp	QCD, %	0.7 (0.4–0.1)	0.8 (0.4–1.5)	1.1 (0.7–2.0)	0.401
	ICC	0.954 (0.892–0.984)	0.830 (0.642–0.936)	0.954 (0.892–0.984)
p-value Friedman: QCD		0.003*	0.014*	0.001*

Note: *Statistical significance for QCD: Pentacam HR vs slitlamp for all the time points: p < 0.05 (Wilcoxon signed rank test corrected acc. Holm-Bonferroni).

Abbreviations: CI, confidence interval; QCD, quartile coefficient of dispersion; ICC, the intra-class correlation coefficient.

Table 3 Descriptive Data of the Average Values (Statistical Median) of Further Corneal Biometric Parameters Measured in the Study: Median (1st Quartile – 3rd Quartile), n = 20

Parameter	Time of the Measurement			Quartile Coefficient of Dispersion, %	p-value Friedman
	8 a.m.	11 a.m.	2 p.m.
CCT, nm	555.8 (522.4–583.0)	561.2 (521.7–583.2)	549.0 (518.7–579.2)	0.5 (0.3–0.8)	0.006*
CCR long, mm	7.78 (7.59–7.91)	7.77 (7.55–7.93)	7.69 (7.58–7.90)	0.2 (0.1–0.3)	0.145
CCR short, mm	7.59 (7.45–7.76)	7.58 (7.41–7.77)	7.54 (7.41–7.74)	0.1 (0.1–0.2)	0.381

Note: *Statistical significance towards the measurement at 2 p.m.: 8 a.m.: p = 0.015; 11 a.m.: p = 0.02 (Wilcoxon signed rank test corrected acc. Holm-Bonferroni).

Abbreviations: CCT, central corneal thickness; CCR, central corneal radius.