OCT corneal epithelial topographic asymmetry as a sensitive diagnostic tool for early and advancing keratoconus

Figures & data

Figure 1 Total corneal (left) and epithelial (right) three-dimensional pachymetry maps. Top, a right eye with topographic variability of 8.4 μm and epithelial range of −28 μm, classified as KC2 (IHD =0.065, ISV =64); bottom, a right eye with topographic variability of 9.6 μm and epithelial range of −30 μm, classified as KC3 (IHD =0.107, ISV =104).

Notes: *Thickness minimum (in both corneal and epithelial maps); ⁺thickness maximum (epithelial map only).
Abbreviations: IHD, index of height decentration; ISV, index of surface variance.

Table 1 Intraindividual-repeatability descriptive statistics for epithelial thickness, as computed by the standard deviation of the respective values obtained by four consecutive acquisitions per eye

		Center	Superior	Inferior	Minimum	Maximum	Topographic variability
Group A KCN (n=160)	Average	1.78	1.92	1.58	1.33	1.72	0.46
	SD	±1.31	±0.99	±1.01	±1.15	±1.30	±0.25
	Maximum	4.50	4.64	4.53	4.29	8.17	1.36
	Minimum	0.02	0.40	0.54	0.25	0.70	0.09
Group B control (n=160)	Average	0.89	1.21	0.73	1.07	1.73	0.19
	SD	±0.75	±0.89	±0.67	±1.02	±1.05	±0.11
	Maximum	2.55	3.41	3.39	4.32	5.07	1.08
	Minimum	0.00	0.10	0.05	0.50	0.70	0.01

Notes: Repeatability is reported for the epithelium at the pupil center (center), superior, inferior, as well as minimum, maximum, and topographic thickness variability. All values are in micrometers.

Abbreviations: KCN, keratoconus; SD, standard deviation.

Figure 2 Box plots of epithelial thickness (showing center, superior, inferior, minimum, maximum, mean, and peripheral) showing median level (⊗), average (⊕), 95% median confidence, and interquartile interval range boxes. Top, keratoconic group; bottom, control group.

Table 2 Central epithelial thickness (center), superior, inferior, minimum, maximum, topographic thickness variability, range, mean, and peripheral for the two study groups (control and keratoconus [KCN])

	Center	Superior	Inferior	Minimum	Maximum	Topographic variability	Range	Mean	Peripheral
Group B control (n=160)	52.54	51.35	53.13	48.50	55.33	1.59	−6.86	52.24	52.18
	±3.23	±3.41	±3.27	±3.98	±3.67	±0.79	±3.33	±3.21	±3.23
	59	60	59	57	64	5.6	−3	59.42	59.50
	45	44	45	28	46	0.6	−29	44.58	44.50
Group A KCN (n=160)	51.75	55.57	49.65	40.73	63.54	6.07	−22.81	52.39	52.52
	±7.02	±6.79	±5.54	±8.51	±8.85	±3.55	±12.55	±5.48	±5.36
	72	76	72	60	94	17.8	−4	70.33	70.00
	36	42	33	19	49	1.5	−66	43.50	43.60
Subgroup A1
KCN	52.90	52.85	52.23	46.85	57.18	2.46	−10.33	52.86	53.32
≤ TKC 1	±5.75	±5.89	±5.10	±5.02	±5.67	±0.75	±3.82	±5.30	±5.25
(n=40)	72	73	69	60	77	3.9	−4	70.33	70.00
	46	46	44	40	49	1.5	−18	45.50	45.00
Subgroup A2
KCN	50.60	58.00	48.71	36.14	70.19	9.27	−34.05	52.29	52.41
≥ TKC 3	±8.46	±8.40	±6.08	±9.20	±8.84	±3.25	±11.31	±6.68	±6.51
(n=58)	67	76	64	56	94	17.8	−14	68.08	68.30
	36	44	38	19	54	3.7	−66	43.58	43.90

Notes: Subgroup A1 was defined by keratoconic patients classified by topographic KCN classification (TKC) less than or equal to 1, and subgroup A2 defined by TKC equal to or greater than 3. All values are in micrometers.

Figure 3 Box plots of epithelial thickness topographic variability (top) and range, defined as minimum minus maximum (bottom) for the two groups. Graphs include median level (⊗), average (⊕), 95% median confidence, and interquartile interval range boxes.

Abbreviation: KCN, keratoconus.

Figure 4 Scatter and fitted-line plots of topographic epithelial thickness variability versus index of height decentration (IHD; top) and index of surface variance (ISV; bottom). Graphs include regression, 95% confidence interval (CI), and 95% prediction interval (PI) lines.

Figure 5 Scatter and fitted-line plots of topographic epithelial thickness range versus index of height decentration (IHD; top) and index of surface variance (ISV; bottom). Graphs include regression, 95% confidence interval (CI), and 95% prediction interval (PI) lines.