Analysis of Scheimpflug Tomography Parameters for Detecting Subclinical Keratoconus in the Fellow Eyes of Patients with Unilateral Keratoconus in the Eastern Province of Saudi Arabia

Figures & data

Table 1 Comparison of Parameters Among the Keratoconus (KC), Forme Fruste Keratoconus (FFKC), and Normal Cornea (NL) Groups

Parameters	NL Group	KC Group	FFKC Group	(NL, KC, FFKC)	(NL vs KC)	(NL vs FFKC)	(KC vs FFKC)
	Mean /Median (Range of Variation)			P-value
K1	42.50 (41.80–43.40)	44.70 (42.00–46.00)	42.70 (41.80–43.50)	0.004	0.001	0.574	0.025
K2	43.76 (42.34–45.18)	47.60 (44.65–51.55)	43.70 (42.27–45.14)	<0.001	<0.001	0.834	<0.001
Km	43.10 (42.40–44.00)	45.45 (43.25–48.38)	43.15 (41.83–44.48)	<0.001	<0.001	0.766	0.001
Kmax	44.20 (43.30–45.20)	53.30 (49.00–60.48)	44.54 (43.00–46.08)	<0.001	<0.001	0.283	<0.001
AstigF	1.10 (0.80–1.60)	3.30 (1.90–5.03)	0.85 (0.50–1.32)	<0.001	<0.001	0.031	<0.001
ISV	17.00 (14.00–20.00)	85.50 (54.00–138.00)	17.00 (14.25–23.00)	<0.001	<0.001	0.316	<0.001
IVA	0.11 (0.08–0.14)	0.92 (0.55–1.53)	0.14 (0.09–0.18)	<0.001	<0.001	0.008	<0.001
KI	1.02 (1.00–1.03)	1.23 (1.00–1.45)	1.02 (1.01–1.04)	<0.001	<0.001	0.029	<0.001
CKI	1.01 (1.00–1.01)	1.04 (1.02–1.10)	1.01 (1.00–1.01)	<0.001	<0.001	0.361	<0.001
IHA	5.10 (2.50–8.40)	17.40 (5.85–35.62)	5.30 (1.55–11.20)	<0.001	<0.001	0.821	<0.001
IHD	0.01 (0.01–0.01)	0.09 (0.05–0.16)	0.01 (0.01–0.01)	<0.001	<0.001	0.627	<0.001
Rmin	7.63 (7.47–7.79)	6.15 (5.09–7.21)	7.58 (7.32–7.85)	<0.001	<0.001	0.285	<0.001
IS Value	0.09 (−0.35–0.36)	6.01 (0.41–11.62)	0.44 (−0.30–1.17)	<0.001	<0.001	0.003	<0.001
KISA	4.34 (1.38–6.67)	621.62 (108.93–2859.62)	11.16 (2.61–20.73)	<0.001	<0.001	0.007	<0.001
PPImin	0.66 (0.59–0.75)	1.35 (1.06–1.95)	0.73 (0.55–0.90)	<0.001	<0.001	0.09	<0.001
PPIave	1.24 (1.05–1.43)	3.31 (2.38–4.13)	1.46 (1.20–1.72)	<0.001	<0.001	<0.001	<0.001
PPImax	0.96 (0.84–1.08)	2.18 (1.67–2.98)	1.06 (0.88–1.24)	<0.001	<0.001	0.004	<0.001
ART Max	446.00 (401.00–488.00)	145.00 (115.75–188.25)	369.00 (320.50–417.00)	<0.001	<0.001	<0.001	<0.001
Df	–0.08 (–0.55–0.42)	9.87 (4.91–12.77)	0.30 (–0.80–1.40)	<0.001	<0.001	0.182	<0.001
Db	–0.49 (–0.87–0.02)	7.63 (4.43–12.56)	–0.01 (–0.53–0.73)	<0.001	<0.001	0.001	<0.001
Dp	0.36 (–0.45–1.16)	7.77 (5.22–12.59)	1.05 (–0.15–2.25)	<0.001	<0.001	0.004	<0.001
Dt	–0.31 (–0.65–0.18)	2.04 (0.88–3.16)	0.09 (–0.35–1.06)	<0.001	<0.001	0.007	<0.001
Da	0.37 (–0.03–0.78)	3.14 (2.74–3.40)	1.05 (0.33–1.77)	<0.001	<0.001	<0.001	<0.001
BAD-D	0.80 (0.22–1.38)	8.54 (5.80–12.09)	1.57 (0.70–2.44)	<0.001	<0.001	<0.001	<0.001
F_Ele_Thin	2.00 (1.00–3.00)	21.50 (10.25–29.75)	3.03 (1.13–4.94)	<0.001	<0.001	0.03	<0.001
B_Ele_Thin	5.00 (3.00–8.00)	57.00 (30.00–74.75)	9.63 (5.24–14.03)	<0.001	<0.001	<0.001	<0.001
RMS HOA	0.38 (0.33–0.44)	3.18 (1.99–4.79)	0.50 (0.42–0.68)	<0.001	<0.001	<0.001	<0.001

Abbreviations: ART max, maximum Ambrósio relational thickness index; AstigF, front topographic astigmatism; B_Ele_Thin, back corneal elevation at the thinnest location; BAD-D, Belin/Ambrỏsio Enhanced Ectasia total deviation; BAD, Belin/Ambrỏsio Enhanced Ectasia Display; CKI, central keratoconus index; Da, deviation of normality of Ambrỏsio relational thickness; Db, deviation of normality of the back elevation; Df, deviation of normality of the front elevation; Dp, deviation of normality of pachymetric progression; Dt, deviation of normality of corneal thinnest point; F_Ele_Thin, front corneal elevation at the thinnest location; FFKC, forme fruste keratoconus; IHA, index of height asymmetry; IHD, index of height decentration; IS value, inferior-superior index; ISV, index of surface variance; IVA, index of vertical asymmetry; K1, flat keratometry; K2, steep keratometry; KC, keratoconus; KI, keratoconus index; KISA, keratometry, IS value, skew percentage, astigmatism index; PPIave, average pachymetric progression index; PPImax, maximum pachymetric progression index; PPImin, minimum pachymetric progression index; Rmin, minimum sagittal curvature; RMS HOA, total higher-order aberrations.

Table 2 Receiver Operator Characteristic (ROC) Curve Analysis Results for Different Parameters in Distinguishing the Keratoconus (KC) and Forme Fruste Keratoconus (FFKC) Groups from the Normal Cornea (NL) Group

Parameters	KC Group vs NL Group				FFKC Group vs NL Group
	AUC	Cut-off	Sensitivity	Specificity	AUC	Cut-off	Sensitivity	Specificity
K1	0.691	43.1	0.6667	0.6822	0.533	42.6	0.5333	0.5116
K2	0.826	44.7	0.7333	0.7364	0.488	43.9	0.5	0.5194
Km	0.752	43.8	0.7	0.6977	0.517	43.3	0.5333	0.5504
Kmax	0.939	46	0.9	0.907	0.563	44.7	0.5667	0.6047
AstigF	0.827	1.8	0.8	0.7907	0.374	1	0.3667	0.3876
ISV	0.999	30	0.9667	0.9767	0.559	17	0.6	0.4729
IVA	0.994	0.2	0.9333	0.938	0.656	0.13	0.6333	0.6822
KI	0.874	1.04	0.8667	0.8605	0.626	1.02	0.6333	0.4884
CKI	0.808	1.02	0.7667	0.9767	0.453	1.01	0.5333	0.3876
IHA	0.761	8.2	0.7333	0.7364	0.487	5.5	0.5	0.5039
IHD	0.961	0.019	0.9333	0.9225	0.528	0.01	0.4667	0.4884
Rmin	0.062	7.36	0.1	0.1085	0.437	7.58	0.4333	0.4341
IS value	0.902	0.75	0.8667	0.8682	0.677	0.22	0.6667	0.6512
KISA	0.949	12.067	0.9	0.907	0.659	5.092	0.5667	0.5736
PPImin	0.921	0.83	0.9	0.9147	0.600	0.7	0.5667	0.5969
PPIave	0.954	1.55	0.9333	0.907	0.741	1.34	0.7333	0.7364
PPImax	0.937	1.13	0.9	0.907	0.669	0.99	0.6	0.6202
ART max	0.053	340	0.1	0.0853	0.241	408	0.3	0.2946
Df	0.979	1.35	0.9333	0.9225	0.578	−0.04	0.5333	0.5271
Db	0.973	0.38	0.9	0.907	0.690	−0.29	0.6	0.6047
Dp	0.937	1.49	0.9	0.907	0.669	0.51	0.6333	0.6124
Dt	0.894	0.6	0.8333	0.8372	0.659	−0.17	0.6333	0.5891
Da	0.954	1.35	0.9333	0.9225	0.740	0.72	0.7	0.7054
BAD-D	0.980	1.75	0.9333	0.938	0.766	1.13	0.7	0.7054
F_Ele_Thin	0.938	5	0.9333	0.9457	0.624	3	0.5667	0.6124
B_Ele_Thin	0.983	12	0.9333	0.9612	0.766	8	0.7	0.7054
RMS HOA	0.972	0.616	0.9667	0.938	0.789	0.425	0.7	0.6977

Abbreviations: ART max, maximum Ambrósio relational thickness index; AstigF, front topographic astigmatism; B_Ele_Thin, back corneal elevation at the thinnest location; BAD-D, Belin/Ambrỏsio Enhanced Ectasia total deviation; BAD, Belin/Ambrỏsio Enhanced Ectasia Display; CKI, central keratoconus index; Da, deviation of normality of Ambrỏsio relational thickness; Db, deviation of normality of the back elevation; Df, deviation of normality of the front elevation; Dp, deviation of normality of pachymetric progression; Dt, deviation of normality of corneal thinnest point; F_Ele_Thin, front corneal elevation at the thinnest location; FFKC, forme fruste keratoconus; IHA, index of height asymmetry; IHD, index of height decentration; IS value, inferior-superior index; ISV, index of surface variance; IVA, index of vertical asymmetry; K1, flat keratometry; K2, steep keratometry; KC, keratoconus; KI, keratoconus index; KISA, keratometry, IS value, skew percentage, astigmatism index; Kmax, maximum keratometry; PPIave, average pachymetric progression index; PPImax, maximum pachymetric progression index; PPImin, minimum pachymetric progression index; Rmin, minimum sagittal curvature; RMS HOA, total higher-order aberrations.

Table 3 Top Five Parameters with the Highest AUC Values Distinguishing the Forme Fruste Keratoconus (FFKC) Group from the Normal Cornea (NL) Group

Parameters	FFKC Group vs NL Group
	AUC	Cut-off	Sensitivity	Specificity
RMS HOA	0.789	0.425	0.7	0.6977
BAD-D	0.766	1.13	0.7	0.7054
B_Ele_Thin	0.766	8	0.7	0.7054
PPIave	0.741	1.34	0.7333	0.7364
Da	0.740	0.72	0.7	0.7054

Abbreviations: AUC, area under the curve; B_Ele_Thin, back corneal elevation at the thinnest location; BAD-D, Belin/Ambrỏsio Enhanced Ectasia total deviation; Da, deviation of normality of Ambrỏsio relational thickness; FFKC, forme fruste keratoconus; PPIave, average pachymetric progression index.

Figure 1 Receiver operating characteristic curve for distinguishing keratoconus from normal corneas.

Abbreviations: ART max, maximum Ambrósio relational thickness index; AstigF, front topographic astigmatism; B_Ele_Thin, back corneal elevation at the thinnest location; BAD-D, Belin/Ambrỏsio Enhanced Ectasia total deviation; CKI, central keratoconus index; Da, deviation of normality of Ambrỏsio relational thickness; Db, deviation of normality of the back elevation; Df, deviation of normality of the front elevation; Dp, deviation of normality of pachymetric progression; Dt, deviation of normality of corneal thinnest point; F_Ele_Thin, front corneal elevation at the thinnest location; IHA, index of height asymmetry; IHD, index of height decentration; IS value, inferior-superior index; ISV, index of surface variance; IVA, index of vertical asymmetry; K1, flat keratometry; K2, steep keratometry; KC, keratoconus; KI, keratoconus index; KISA, keratometry, IS value, skew percentage, astigmatism index; Km, mean keratometry; Kmax, maximum keratometry; PPIave, average pachymetric progression index; PPImax, maximum pachymetric progression index; PPImin, minimum pachymetric progression index; Rmin, minimum sagittal curvature; RMS HOA, total higher-order aberrations.

Figure 2 Receiver operating characteristic curve for distinguishing forme fruste keratoconus from normal corneas.

Abbreviations: ART max, maximum Ambrósio relational thickness index; AstigF, front topographic astigmatism; B_Ele_Thin, back corneal elevation at the thinnest location; BAD-D, Belin/Ambrỏsio Enhanced Ectasia total deviation; CKI, central keratoconus index; Da, deviation of normality of Ambrỏsio relational thickness; Db, deviation of normality of the back elevation; Df, deviation of normality of the front elevation; Dp, deviation of normality of pachymetric progression; Dt, deviation of normality of corneal thinnest point; F_Ele_Thin, front corneal elevation at the thinnest location; IHA, index of height asymmetry; IHD, index of height decentration; IS value, inferior-superior index; ISV, index of surface variance; IVA, index of vertical asymmetry; K1, flat keratometry; K2, steep keratometry; KC, keratoconus; KI, keratoconus index; KISA, keratometry, IS value, skew percentage, astigmatism index; Km, mean keratometry; Kmax, maximum keratometry; PPIave, average pachymetric progression index; PPImax, maximum pachymetric progression index; PPImin, minimum pachymetric progression index; Rmin, minimum sagittal curvature; RMS HOA, total higher-order aberrations.

Table 4 Comparison of the Receiver Operator Characteristic (ROC) Curves of Some Parameters in the Keratoconus (KC), Forme Fruste Keratoconus (FFKC), and the Normal Cornea (NL) Groups

Parametric Curves Compared		P-value (KC vs NL)	P-value (FFKC vs NL)
ISV	IVA	0.191	0.047
	Df	0.113	0.751
	Da	0.149	0.006
	BAD-D	0.183	<0.001
	RMS HOA	0.297	<0.001
	B_Ele_Thin	0.273	0.001
IVA	Df	0.267	0.131
	Da	0.157	0.233
	BAD-D	0.223	0.076
	PPIave	0.16	0.245
	RMS HOA	0.339	0.028
	B_Ele_Thin	0.399	0.08
Df	Da	0.478	0.019
	BAD-D	0.958	<0.001
	PPIave	0.48	0.023
	RMS HOA	0.81	0.003
	B_Ele_Thin	0.81	0.002
Da	BAD-D	0.131	0.449
	PPIave	1	0.945
	RMS HOA	0.543	0.455
	B_Ele_Thin	0.119	0.645
BAD-D	PPIave	0.135	0.531
	RMS HOA	0.725	0.743
	B_Ele_Thin	0.507	0.998
PPIave	RMS HOA	0.554	0.472
	B_Ele_Thin	0.117	0.646
RMS HOA	B_Ele_Thin	0.671	0.766

Abbreviations: B_Ele_Thin, back corneal elevation at the thinnest location; BAD-D, Belin/Ambrỏsio Enhanced Ectasia total deviation; Da, deviation of normality of Ambrỏsio relational thickness; Df, deviation of normality of the front elevation; FFKC, forme fruste keratoconus; ISV, index of surface variance; IVA, index of vertical asymmetry; PPIave, average pachymetric progression index; RMS HOA, total higher-order aberrations.