Table 1

Comparison between the three groups (DS group, mild keratoconus group and control group) in relation to keratometry, shape indices and keratoconus indices of the posterior corneal surface

	DS group				Mild keratoconus group				Control group				P value
	Cases, no.	Minimum	Maximum	Mean (SD)	Cases, no.	Minimum	Maximum	Mean (SD)	Cases, no.	Minimum	Maximum	Mean (SD)	DS group – mild keratoconus group	DS group – control group	Mild keratoconus group – control group
Keratometry (posterior surface)
KM 3 mm	37	−8.1	−5.8	−6.49±0.38	46	−7.76	−5.05	−6.58±0.54	40	−6.57	−5.59	−6.19±0.25	0.92	<0.01	<0.001
KM 5 mm	37	−7.77	−4.5	−6.39±0.44	46	−7.3	−5.27	−6.48±0.41	40	−6.55	−5.59	−6.18±0.24	0.11	0.001	<0.001
KM 7 mm	37	−7.47	−4.51	−6.30±0.44	46	−7.04	−5.44	−6.38±0.34	40	−6.5	−5.56	−6.15±0.22	0.18	<0.05	<0.001
Shape Indices
rf 4,5 mm	37	−8.11	−5.67	−6.35±0.40	46	−7.66	−4.46	−6.38±0.58	40	−6.44	−5.43	−6.03±0.25	1	<0.01	<0.01
rs 4,5 mm	37	−8.52	−6.23	−6.72±0.43	46	−9.01	−5.22	−7.12±0.77	40	−6.84	−5.66	−6.36±0.28	<0.01	<0.001	<0.001
Q 4,5 mm	37	−3.76	2.26	−0.30±0.80	46	−2.84	3.57	−0.50±1.31	40	−0.65	0.31	−0.11±0.25	0.05	0.01	0.01
RMS/A 4,5 mm	37	0.07	1.12	0.22±0.22	46	0.07	1.66	0.46±0.34	40	0.05	0.24	0.09±0.03	<0.001	<0.001	<0.001
rf 8 mm	37	−8.09	−6.02	−6.38±0.37	46	−7.99	−5.28	−6.48±0.47	40	−6.5	−5.6	−6.12±0.25	0.08	0.001	<0.001
rs 8 mm	37	−8.68	−6.23	−6.66±0.41	46	−8.66	−5.44	−6.94±0.60	40	−6.85	−5.7	−6.35±0.27	<0.01	<0.001	<0.001
Q 8 mm	37	−1.03	−0.04	−0.34±0.23	46	−1.57	0.6	−0.60±0.50	40	−0.66	0.1	−0.29±0.20	<0.01	0.82	0.001
RMS/A 8 mm	37	0.1	0.95	0.25±0.21	46	0.08	1.12	0.37±0.22	40	0.06	0.27	0.14±0.05	<0.001	<0.01	<0.001
Keratoconus Indices
Sib (D)	37	−1.43	2.63	0.23±0.65	46	−0.62	4.39	1.21±1.08	40	−0.2	0.22	0.03±0.10	<0.001	<0.05	<0.001
BCVb (µm)	37	0	6.67	0.77±1.31	46	0	8.37	2.25±1.92	40	0	0.7	0.19±0.23	<0.001	0.001	<0.001
KVb (µm)	37	8	238	33.22±44.29	46	13	165	48.17±33.89	40	5	17	10.63±2.88	0.001	<0.001	<0.001
ThKMin (µm)	37	381	544	492.14±36.31	46	430	602	484.94±33.03	40	480	600	536.13±31.30	0.07	<0.001	<0.001

BCVb, posterior corneal aberrations; D, dioptres; DS, Down syndrome; KM, mean keratometry; KVb, posterior vertex of the ectatic area; Q, asphericity; rf, flat radius; RMS/A, root mean square per unit of area; rs, steepest radius; Sib, posterior symmetry index; ThkMin, minimal thickness.