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Table 1 The tolerance indices (Tr, TR)

From: Identifying more reliable parameters for the detection of change during the follow-up of mild to moderate keratoconus patients

  Repeatability Reproducibility
  Single Pair Triplet
Anterior Tr TR TR TR
 K1 (D) −0.12 −0.43 −2.00 −4.33
 K2 (D) −0.08 0.12 −3.39 −0.57
 Km (D) 0.16 0.08 −1.59 −0.23
 Axis (deg) −2.17 −2.84 −2.90 −4.39
 Q-value, 30 deg 0.73 0.78 0.62 0.89
 Rper (mm) 1.02 0.43 1.49 1.16
 Rmin (mm) 0.33 0.52 −0.02 −0.23
Posterior
 K1 (D) 0.89 0.51 1.03 1.26
 K2 (D) 0.92 0.89 −1.77 0.39
 Km (D) 0.33 0.59 0.79 1.06
 Q-value, 30 deg     
 Rper (mm) 0.55 0.24 0.29 −0.83
 Rmin (mm) 0.73 0.90 1.33 0.57
Summary data
 Kmax front (D) 0.90 1.06 0.50 0.12
 X-axis (mm) −1.79 −1.03 −0.90 −0.93
 Y-axis (mm) −1.78 −2.15 −3.54 −2.43
 Corneal volume (mm3) 0.13 0.86 0.58 0.12
 KPD (D) 0.58 0.52 −0.16 −0.86
 AC volume (mm3) 0.80 −0.11 −0.84 −0.81
 AC angle (deg) 0.25 0.60 −0.08 −1.99
 AC depth (mm) 1.31 0.35 −1.26 −0.60
 Pupil diameter (mm) −0.22 −0.77 −0.11 −0.19
Pachymetry
 Pupil centre (μm) −1.98 −1.45 −1.99 −2.21
 X-axis (mm) −4.61 −5.32 −8.32 −7.48
 Y-axis (mm) −3.96 −6.12 −6.16 −4.91
 Apex (μm) 0.17 1.05 0.70 0.24
 TCT (μm) −0.42 1.09 0.92 0.77
Corneal volume (mm3)
 3 mm diameter −2.31 −0.60 −0.56 −0.78
 5 mm diameter −1.55 −0.75 −1.01 −1.32
 7 mm diameter −0.25 0.85 0.59 0.19
Indices
 ISV 1.04 −0.32 −1.11 0.22
 IVA 1.02 1.35 0.88 −0.38
 KI −0.08 0.92 0.72 0.52
 CKI −0.08 −1.61 −2.51 −2.76
 IHA 2.09 2.41 2.49 2.43
 IHD −1.10 −1.66 −0.57 −0.73
  1. K1, K2 = Keratometry readings 1,2; Km = Mean keratometry reading; Rper = Mean radius of curvature in the 7-9 mm area of the cornea; Rmin = Minimum radius of curvature; KPD = Keratometric power deviation; AC = Anterior chamber; ISV = Index of surface variance; IVA = Index of vertical asymmetry; KI = Keratoconus index; CKI = Centre keratoconus index; IHA = Index of height asymmetry; IHD = Index of height decentration; Sr = Within-subject standard deviation; r = The limits of repeatability; Tr = The log of the ratio between the limits of repeatability of keratoconus patients and normal subjects; −0.45 < Tr/TR < 0.45 is within normative limits
  2. Example of reading the table: Taking the line Kmax, r is 1.97 D, therefore it has a Tr value of 0.9, which means that r limit of 1.97 is well outside normal limits, R is 2.3 D, therefore it has a TR value of 1.06 is reported when a single image is used, again indicating that this is well outside normal limits, TR reduces to 0.12 when the average of three images was used, which is not significantly different than normal limits