Diagnostic accuracy of different keratoconus detection indices of pentacam in paediatric eyes

Abstract

Objective: No diagnostic gold standard for keratoconus in children and adolescents exists. Our objective was investigating the diagnostic accuracy of various indices for keratoconus (KC) detection in paediatric eyes.

Methods: All retrievable data of significance from 432 normal right paediatric eyes and 48 eyes of paediatric KC and forme fruste KC (FFKC), imaged by use of a rotating Scheimpflug camera (Oculyzer II, Pentacam HR) between December 2013 and October 2018 at Watany Eye Hospitals, Cairo, Egypt, including Scheimpflug images data, were collected. The area under the receiver operating characteristic curve (AUROC) was calculated for different indices in this retrospective descriptive study.

Results: All 36 tested indices showed discriminative power differentiating KC and FFKC from normal corneas (AUROC P-value <0.05), except AC volume, AC angle, and horizontal decentrations of the steepest and thinnest points. The 32 indices showed variable degrees of diagnostic accuracy. The highest AUROC was that of the corneal assessment index from the relational thickness and other OCULUS values (CAIRO 8). Only 8 indices showed non-inferiority to it, namely, Ambrosio's relational thickness maximum (ART max) and avg, the pachymetric progression index maximum (PPI max) and avg, the back elevation from the best-fit toric ellipsoid (BE BFTE), the KC index (KI), the topographic KC indices (TKC), and the index of height decentration (IHD) (P > 0.05).

Conclusions: The 8 most useful rotating Scheimpflug imaging indices for KC detection in paediatric eyes are CAIRO 8 followed by ART max and avg, PPI max and avg, BE BFTE, KI, TKC, and IHD.

Fig. 1. The AUROC of different tomographic indices in the studied population.

TP x thinnest point displacement in the x-axis, K Max Front x steepest point of the front surface keratometry displacement in the x-axis, ACA maximum anterior chamber angle in the horizontal meridian, ACV anterior chamber volume at 10-mm diameter, keratometric astigmatism (absolute value), TP y thinnest point displacement in the y-axis, ACD internal anterior chamber depth, K mean curvature power of the cornea within the central 3-mm circle expressed in diopters, K Max y Front steepest point of the front surface keratometry displacement in the y axis, Irregularity high-order irregularity by Fourier analysis (other than spherical power and asphericity, tilt, and astigmatism), IHA index of height asymmetry, K2 keratometric power of the steep meridian, K1 keratometric power of the flat meridian, TNP Apex true net power at the corneal apex, Tilt tilt by Fourier analysis, Pachy pupil corneal thickness at the point corresponding to the pupil centre, Pachy apex corneal thickness at the apex, Ecc Sph mean eccentricity in the central 30 degrees by Fourier analysis, ISV index of surface variance, TP corneal thickness at the thinnest point, K max front keratometry of the steepest point of the front surface, FE BFS front elevation from the best-fit sphere, PPI min minimum pachymetric progression index, FE BFTE front elevation from the best-fit toric ellipsoid, IVA index of vertical asymmetry, CKI central keratoconus index, BE back elevation from the best-fit sphere, IHD index of height decentration, TKC topographic keratoconus indices, BE BFTE back elevation from the best-fit toric ellipsoid, KI keratoconus index, PPI avg average pachymetric progression index, ART avg Ambrosio’s relational thickness average, PPI Max maximum pachymetric progression Index, ART max Ambrosio’s relational thickness maximum, CAIRO 8 corneal assessment index from the relational thickness and other OCULUS values analysed for an 8-mm zone.

Fig. 2. The sensitivities and specificities of all the tomographic indices.

TP x thinnest point displacement in the x-axis, K Max Front x steepest point of the front surface keratometry displacement in the x-axis, ACA maximum anterior chamber angle in the horizontal meridian, ACV anterior chamber volume at 10-mm diameter, keratometric astigmatism keratometric astigmatism (absolute value), TP y thinnest point displacement in the y-axis, ACD internal anterior chamber depth, K mean mean curvature power of the cornea within the central 3-mm circle expressed in diopters, K Max y Front steepest point of the front surface keratometry displacement in the y-axis, Irregularity high-order irregularity by Fourier analysis (other than spherical power and asphericity, tilt, and astigmatism), IHA index of height asymmetry, K2 keratometric power of the steep meridian, K1 keratometric power of the flat meridian, TNP Apex true net power at the corneal apex, Tilt tilt by Fourier analysis, Pachy pupil corneal thickness at the point corresponding to the pupil centre, Pachy apex corneal thickness at the apex, Ecc Sph mean eccentricity in the central 30 degrees by Fourier analysis, ISV index of surface variance, TP corneal thickness at the thinnest point, K max front keratometry of the steepest point of the front surface, FE BFS front elevation from the best-fit sphere, PPI min minimum pachymetric progression index, FE BFTE front elevation from the best-fit toric ellipsoid, IVA index of vertical asymmetry, CKI central keratoconus index, BE back elevation from the best-fit sphere, IHD index of height decentration, TKC topographic keratoconus indices, BE BFTE back elevation from the best-fit toric ellipsoid, KI keratoconus index, PPI avg average pachymetric progression index, ART avg Ambrosio’s relational thickness average, PPI Max maximum pachymetric progression Index, ART max Ambrosio’s relational thickness maximum, CAIRO 8 corneal assessment index from the relational thickness and other OCULUS values analysed for an 8-mm zone.

Fig. 3. The AUROC of all the tomographic indices in patients below and above 12 years old.

PMinX_nas thinnest point displacement in the x-axis, K_Max_X_Front steepest point of the front surface keratometry displacement in the x-axis, Ch._Angle maximum anterior chamber angle in the horizontal meridian, AC_Volume_10 _mm anterior chamber volume at 10-mm diameter, Asti. Central keratometric astigmatism keratometric astigmatism (absolute value), PMinY_sup thinnest point displacement in the y-axis, AC_Depth internal anterior chamber depth, K mean mean curvature power of the cornea within the central 3-mm circle expressed in diopters, K_Max_y_Front steepest point of the front surface keratometry displacement in the y-axis, Irregul high-order irregularity by Fourier analysis (other than spherical power and asphericity, tilt, and astigmatism), IHA index of height asymmetry, K2 keratometric power of the steep meridian, K1 keratometric power of the flat meridian, TNPApex true net power at the corneal apex, Tilt_Min_MVP tilt by Fourier analysis, PachyPupil corneal thickness at the point corresponding to the pupil centre, PachyApex corneal thickness at the apex, Ecc mean eccentricity in the central 30 degrees by Fourier analysis, ISV index of surface variance, TKC topographic keratoconus indices, K_max_front_keratometry of the steepest point of the front surface, FE front elevation from the best-fit sphere, RPI_Min minimum pachymetric progression index, FE_BFTE front elevation from the best-fit toric ellipsoid, IVA index of vertical asymmetry, CKI central keratoconus index, BE back elevation from the best-fit sphere, IHD index of height decentration, TKC topographic keratoconus indices, BE_BFTE back elevation from the best-fit toric ellipsoid, KI keratoconus index, RPI_Mid average pachymetric progression index, ART_avg Ambrosio’s relational thickness average, RPI_Max maximum pachymetric progression Index, ART_max Ambrosio’s relational thickness maximum, CAIRO_8 Corneal Assessment Index from the Relational thickness and other OCULUS values analysed for an 8-mm zone.