Geometric variable
Description
Figure in which is represented
Total corneal volume [mm3]
Volume limited by front, back, and peripheral surfaces of the solid model generated
1
Anterior corneal surface area [mm2]
Area of the front/exterior surface
1
Posterior corneal surface area [mm2]
Area of the rear/interior surface
1
Total corneal surface area [mm2]
Sum of anterior, posterior, and perimetral corneal surface areas of the solid model generated
1
Sagittal plane area in apex [mm2]
Area of the cornea within the sagittal plane passing through the Z axis and the highest point (apex) of the anterior corneal surface
2
Anterior and posterior apex deviation [mm]
Average distance from the Z axis to the highest point (apex) of the anterior/posterior corneal surfaces
2
Sagittal plane area at minimum thickness point [mm2]
Area of the cornea within the sagittal plane passing through the Z axis and the minimum thickness point (maximum curvature) of the anterior corneal surface
3
Anterior and posterior minimum thickness point deviation [mm]
Average distance in the XY plane from the Z axis to the minimum thickness points (maximum curvature) of the anterior/posterior corneal surfaces
3
Centre of mass X, Y, Z [mm]
Centre of mass coordinates X, Y, Z of the solid
–
Net deviation from centre of mass in XY [mm]
Projective XY Modulus of the centre of mass
–
Volume of corneal cylinder R−x [mm3]
Volume of the intersection in 3D between the solid model of the cornea generated and a cylinder with x radius whose axis passes through the minimum thickness points (maximum curvature) of the anterior and posterior corneal surfaces. Radii adopted for this study were 0.5, 1, 1.5, and 2 mm
4
11.2.4 Data Analysis
According to data engagement scores (K-S test), a Student’s t-test or U-Mann–Whitney Wilcoxon test was employed, as appropriate. ROC curves were established in order to determine what parameters could be used to classify diseased corneas, calculating optimal cutoffs, sensitivity, and specificity. All analyses were performed using Graphpad Prism 6 and SPSS 17.0 software.
11.3 Results
Table 11.2 summarizes the main outcomes of the variables analyzed in this study. The majority of modeled variables have statistically significant differences when comparing healthy with diseased corneas, as presented in Table 11.2 .
Table 11.2
Descriptive values (mean, standard deviation, 95 % CI, minimum, maximum, and 25th, 50th, and 75th percentiles) and differences between normal and subclinical keratoconus corneal variables modeled
Measurement | Normal group, n = 89 | Subclinical keratoconus group, n = 31 | p (statistical test) | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
M | SD | (95 % CI) | Min–Max | P25 | P50 | P75 | M | SD | (95 % CI) | Min–Max | P25 | P50 | P75 | ||
Total corneal volume [mm3] | 25.79 | 1.60 | (24.45–26.13) | 21.36–29.47 | 24.62 | 25.93 | 26.82 | 24.01 | 1.71 | (23.38–24.63) | 19.82–28.10 | 22.96 | 23.82 | 24.60 | 0.000 (t-test) |
Anterior corneal surface area [mm2] | 43.08 | 0.15 | (43.05–43.11) | 42.73–43.39 | 42.98 | 43.07 | 43.20 | 43.19 | 0.17 | (43.12–43.25) | 42.81–43.50 | 43.05 | 43.21 | 43.33 | 0.002 (t-test) |
Posterior corneal surface area [mm2] | 44.23 | 0.28 | (44.17–44.29) | 43.49–44.87 | 44.04 | 44.24 | 44.41 | 44.38 | 0.29 | (44.28–44.49) | 43.83–44.80 | 44.13 | 44.40 | 44.63 | 0.011 (t-test) |
Total corneal surface area [mm2] | 103.93 | 1.27 | (103.67–104.19) | 100.73–106.16 | 103.10 | 103.91 | 105.09 | 103.24 | 1.18 | (102.81–103.67) | 101.28–105.57 | 102.35 | 103.30 | 104.02 | 0.010 (t-test) |
Sagittal plane are a in apex [mm2] | 4.33 | 0.27 | (4.27–4.38) | 3.58–5.00 | 4.13 | 4.35 | 4.50 | 4.01 | 0.30 | (3.90–4.12) | 3.27–4.77 | 3.85 | 3.98 | 4.10 | 0.000 (t-test) |
Sagittal plane area at minimum thickness point [mm2] | 4.27 | 0.53 | (4.16–4.39) | 0.00–5.00 | 4.11 | 4.35 | 4.48 | 4.00 | 0.30 | (3.89–4.11) | 3.27–4.76 | 3.84 | 3.98 | 4.10 | 0.000 (Mann–Whitney) |
Anterior apex deviation [mm] | 0.00 | 0.00 | (0.00–0.00) | 0.00–0.00 | 0.00 | 0.00 | 0.00 | 0.01 | 0.03 | (−0.0009–0.0198) | 0.00–0.16 | 0.00 | 0.01 | 0.01 | 0.000 (Mann–Whitney) |
Posterior apex deviation [mm] | 0.08 | 0.02 | (0.07–0.08) | 0.03–0.14 | 0.06 | 0.07 | 0.09 | 0.16 | 0.08 | (0.13–0.19) | 0.06–0.39 | 0.11 | 0.14 | 0.21 | 0.000 (Mann–Whitney) |
Anterior minimum thickness point deviation [mm] | 0.88 | 0.27 | (0.82–0.93) | 0.46–2.18 | 0.70 | 0.82 | 0.99 | 1.15 | 0.33 | (1.02–1.27) | 0.59–1.81 | 0.85 | 1.14 | 1.42 | 0.000 (Mann–Whitney) |
Posterior minimum thickness point deviation [mm] | 0.81 | 0.25 | (0.76–0.86) | 0.44–1.95 | 0.65 | 0.77 | 0.90 | 1.07 | 0.31 | (0.96–1.19) | 0.54–1.72 | 0.79 | 1.08 | 1.33 | 0.000 (Mann–Whitney) |
Net deviation from centre of mass XY [mm] | 0.06 | 0.02 | (0.05–0.06) | 0.01–0.10 | 0.04 | 0.06 | 0.07 | 0.07 | 0.02 | (0.06–0.07) | 0.03–0.11 | 0.05 | 0.06 | 0.08 | 0.042 (t-test) |
Centre of mass X [mm] | 0.04 | 0.02
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