Repeatability of OCT-Based versus Scheimpflug- and Reflection-Based Keratometry in Patients with Hyperosmolar and Normal Tear Film

Figures & data

Table 1 Demographics, Osmolarity and Keratometry by Osmolarity Group

	Hyperosmolar, n = 31	Control, n = 63	p
	Mean ± SD (Range)	Mean ± SD (Range)
Sex, f	48.4%	54.0%	0.77^a
Age	44.7 ± 8.4 (30 to 68)	42.4 ± 8.3 (27–62)	0.04^b,*
Previous LVC	38.7%	31.7%	0.66^a
Osmolarity	326 ± 12 (316 to 365)	298 ± 7 (281–308)	<0.01^b,*
Average SimK^c (D)	42.39 ± 2.14 (36.24 to 46.53)	43.01 ± 1.93 (38.25–47.49)	0.02^b,*
SimK Astigmatism^c,d (D)	1.06 ± 0.65 (0.12 to 3.35)	1.3 ± 1.1 (0.02–6.38)	0.23^b

Notes: ^aPearson’s χ² test. ^bWilcoxon rank-sum test. ^cMean of all instruments. ^dMagnitude of astigmatism. *Statistically significant.

Abbreviations: LVC, laser vision correction; SimK, simulated keratometry.

Table 2 Mean Absolute Difference and Standard Deviation Between Repeated Measurements of (A) Average K and (B) Astigmatism

	Hyperosmolar Group				Control Group
A Average K absolute difference (D)	Lenstar n = 31	Pentacam n = 28	Casia n = 31	Anterion n = 16	Lenstar n = 61	Pentacam n = 58	Casia n = 62	Anterion n = 32
	Mean ± SD (Range)	Mean ± SD (Range)  p (padj)	Mean ± SD (Range)  p (padj)	Mean ± SD (Range)  p (padj)	Mean ± SD (Range)	Mean ± SD (Range)  p (padj)	Mean ± SD (Range)  p (padj)	Mean ± SD (Range)  p (padj)
Average SimK	0.04 ± 0.03 (0–0.11)	0.04 ± 0.04 (0–0.11) 0.89^a (1^a)	0.08 ± 0.06 (0–0.14) 0.001^a  (0.011^a,*)	0.11 ± 0.08 (0– 0.28) 0.004^a  (0.032^a,*)	0.06 ± 0.06 (0– 0.23)	0.05 ± 0.06 (0– 0.20) 0.85^a (1^a)	0.10 ± 0.10 (0– 0.56) 0.002^a  (0.020^a,*)	0.10 ± 0.09 (0– 0.39) 0.026^a (0.210^a)
Average PCP		0.022 ± 0.016 (0.001–0.063)	0.008 ± 0.009 (0– 0.045) 0.002^b,*	0.006 ± 0.004 (0– 0.011) 0.001^b,*		0.013 ± 0.011 (0 – 0.056)	0.009 ± 0.011 (0– 0.083) 0.006^b,*	0.004 ± 0.005 (0– 0.017) <0.001^b,*
Average TCP		0.06 ± 0.04 (0–0.15)	0.09 ± 0.07 (0– 0.28) 0.03^b,*	0.12 ± 0.09 (0– 0.32) 0.04^b,*		0.07 ± 0.06 (0– 0.25)	0.10 ± 0.11 (0– 0.60) 0.015^b,*	0.12 ± 0.10 (0– 0.42) 0.08^b
B Astigmatism vector difference (D)
SimK Astigmatism	0.16 ± 0.12 (0.01– 0.52)	0.14 ± 0.08 (0.01– 0.34) 0.52^a (1^a)	0.21 ± 0.14 (0.01– 0.61) 0.12^a (0.84^a)	0.17 ± 0.10 (0.05– 0.38) 0.46^a (1^a)	0.19 ± 0.15 (0– 0.76)	0.18 ± 0.11 (0– 0.60) 0.674^a (1^a)	0.29 ± 0.23 (0– 1.55) <0.001^a (0.006^a,*)	0.18 ± 0.11 (0–0.41) 0.442^a (1^a)
PCP Astigmatism		0.060 ± 0.04 (0.011– 0.189)	0.033 ± 0.019 (0.007– 0.076) 0.03^b,*	0.021 ± 0.009 (0.009– 0.037) 0.006^b,*		0.049 ± 0.028 (0.01- 0.117)	0.037 ± 0.047 (0.01– 0.367) <0.001^b,*	0.021 ± 0.013 (0– 0.049) <0.001^b,*
TCP Astigmatism		0.17 ± 0.08 (0.04– 0.36)	0.22 ± 0.15 (0.03– 0.63) 0.45^b	0.18 ± 0.11 (0.06– 0.38) 0.78^b		0.18 ± 0.12 (0.01– 0.79)	0.31 ± 0.25 (0.06– 1.77) 0.007^b,*	0.19 ± 0.11 (0– 0.40) 0.769

Notes: ^aWilcoxon signed-rank test comparison with the Lenstar; ^bWilcoxon signed-rank test comparison with the Pentacam. *Statistically significant.

Abbreviations: K, keratometry or corneal power; SD, standard deviation; SimK, simulated keratometry; PCP, posterior corneal power; TCP, total corneal power; Average, difference in average K; Astigmatism, magnitude of vector difference of astigmatism; p_adj, Holm–Bonferroni adjusted p-value for 12 comparisons (Sim K average and astigmatism).

Figure 1 Absolute difference of repeated measurements of (A) average SimK and TCP and (B) average PCP.

Notes: ^aWilcoxon signed-rank test comparison with the Lenstar; ^bWilcoxon signed-rank test comparison with the Pentacam; ^cHolm–Bonferroni adjusted p (12 comparisons). *Statistically significant.

Abbreviations: Difference, absolute difference of repeated measurements; Avg, average; SimK, simulated keratometry; TCP, total corneal power; PCP, posterior corneal power; SD, standard deviation.

Figure 2 Percentage of subjects with (A) average K differences and (B) vector differences greater than certain values.

Notes: ^aFisher exact test comparison with the Pentacam; ^bthe Anterion compared with corresponding data from the Pentacam. *Statistically significant.

Abbreviations: Avg, average; SimK, simulated keratometry; PCP, posterior corneal power; TCP, total corneal power; diff, absolute difference in average K; Ast. diff, magnitude of vector difference of astigmatism.

Figure 3 Difference of repeated measurements of (A) SimK and TCP vector astigmatism and (B) PCP vector astigmatism.

Notes: ^aWilcoxon signed-rank test comparison with the Lenstar; ^bWilcoxon signed-rank test comparison with the Pentacam; ^cHolm–Bonferroni adjusted p (12 comparisons). *Statistically significant.

Abbreviations: Difference, absolute difference of repeated measurements; SimK, simulated keratometry; TCP, total corneal power; PCP, posterior corneal power; Vector Ast., magnitude of vector difference of astigmatism; SD, standard deviation.

Table 3 Coefficient of Repeatability

	Hyperosmolar				Control
K (D)	Lenstar n = 31	Pentacam n = 28	Casia n = 31	Anterion n = 16	Lenstar n = 61	Pentacam n = 58	Casia n = 62	Anterion n = 32
	CR	CR	CR	CR	CR	CR	CR	CR
Average SimK	0.10	0.11	0.20	0.26	0.16	0.14	0.28	0.26
Average PCP		0.05	0.02	0.01		0.03	0.03	0.01
Average TCP		0.13	0.22	0.28		0.17	0.29	0.30
SimK Astigmatism	0.38	0.32	0.50	0.39	0.46	0.41	0.73	0.41
PCP Astigmatism		0.15	0.07	0.05		0.11	0.12	0.05
TCP Astigmatism		0.37	0.51	0.41		0.43	0.78	0.43

Abbreviations: K, keratometry or corneal power; CR, coefficient of repeatability; SimK, anterior keratometry; PCP, posterior corneal power; TCP, total corneal power; Average, difference in average K; Astigmatism, magnitude of vector difference of astigmatism; CR, coefficient of repeatability.

Figure 4 Difference of repeated measurements of (A) average keratometry and (B) vector difference of astigmatism with all subjects.

Notes: ^aWilcoxon signed-rank test comparison with the Lenstar; ^bWilcoxon signed-rank test comparison with the Pentacam; ^cHolm–Bonferroni adjusted p (six comparisons). *Statistically significant.

Abbreviations: Difference, absolute difference of repeated measurements; SimK, simulated keratometry; TCP, total corneal power; PCP, posterior corneal power; Avg, average; Vector Ast, magnitude of vector difference of astigmatism; SD, standard deviation.

Figure 5 Coefficient of repeatability for each instrument with all subjects.

Abbreviations: SimK, simulated keratometry; TCP, total corneal power; PCP, posterior corneal power; Avg, average; Ast., magnitude of vector difference of astigmatism.