Sixty four phakic (from 35 children), 34 pseudophakic (20 patients), and 33 aphakic (19 patients) eyes were eligible to be included in the study. We were not be able to obtain all the four measurements from 29 eyes because of the subject's fatigue, lack of cooperation, or ocular nystagmus. Therefore, the measurements taken from totally 102 eyes (53 phakic, 29 pseudophakic, and 20 aphakic eyes) were included in our analyses.
The ages of all the participants were within the range of 5 - 18 years. The mean ages (±SD) in phakic, pseudophakic, and aphakic groups were 9.75 (±3.3), 9.9 (±2.3), and 8.2 (±2.8) years respectively.
There were 15 phakic (53.5%) males, 9 pseudophakic (50%), and 8 aphakic (66.6%) males.
The mean CCTs (±SE) for phakic cases using Pentacam, PCI, UP, and SM were 549.7 (±5.0), 546.5 (±4.5), 565.9 (±5.5), and 506.2 (±4.4) mm respectively, as shown in Figure 1. There was a significant difference among the measurements within the phakic group (P < 0.001) with the SM being significantly lower than the other three methods (P < 0.001) and the UP being significantly greater than the PCI (P = 0.03). Moreover, the mean CCTs (±SE) for pseudophakic subjects using Pentacam, PCI, UP, and SM were 570.1 (±6.4), 565.0 (±6.1), 571.9 (±6.3), and 524.3 (±6.3) mm respectively. The measurements were significantly different (P < 0.001) with the SM being significantly lower than the other three measurements (P < 0.001). In addition, mean Pentacam-, PCI-, UP-, and SM-measured CCTs (±SE) for aphakic cases were 635.3 (±14.2), 635.4 (±14.5), 649.0 (±13.5), and 589.1 (±13.3) mm respectively. There was a significant difference among the four measurements (P = 0.02) with the SM being significantly lower than the UP (P = 0.02). Taken together, CCT measurements with SM were lower than those of Pentacam, PCI, and UP particularly in phakic and pseudophakic groups. We will further illustrate it in the next figures.
The scatter plots for the six pairs of the methods for the 53 phakic, 29 pseudophakic, and 20 aphakic eyes are presented in Figure 2. The dash-dotted lines show the lines of equality for every pair of the methods, and the solid lines represent the correlation between the pairs of the methods. The correlation between each pair of the methods is high where the maximum correlation is between Pentacam and PCI, SM and PCI, and SM and Pentacam. However, the solid regression line has the most proximity to the dash-dotted equality line for the Pentacam-PCI pair.
The agreements between the six pairs of the methods are further illustrated using the Bland-Altman plots in Figure 3. The Bland-Altman plots show the overall mean difference and 95% level of agreement between the pairs of the methods. The maximum agreement is between Pentacam and PCI, followed by Pentacam and UP, and PCI and UP.
Taken Figures 2 and 3 together, Pentacam and PCI are found to have the closest agreement, whereas SM has the poorest agreement with the other three methods. The overall difference between Pentacam- and PCI-measured CCTs is 3.1 mm. By contrast, the overall SM-measured CCTs are lower than the Pentacam- and PCI- measured CCTs by 44.7 and 41.6 mm respectively. The differences within phakic and pseudophakic groups are greater than that in aphakic cases, as shown in Fig 1.
Furthermore, Fig 3 shows that the overall UP-measured CCTs are slightly greater than the Pentacam- and PCI-measured CCTs by 11.6 and 14.7 mm respectively. The differences within phakic and aphakic groups are greater than that in pseudophakic children, as shown in Fig 1.