Long Term Corneal Flattening After Corneal Crosslinking in Patients with Progressive Keratoconus

Figures & data

Table 1 Pre and Postoperative Visual, Refractive, and Tomographic Data in the studied population

Variable	Pre CXL	Post CXL 1y	Post CXL +10y	P value*
UCVA (logMAR)	0.89 ± 0.64	0.73 ± 0.52	0.61 ± 0.47	0.007
BCVA (logMAR)	0.16 ± 0.15	0.12 ±0.13	0.09 ± 0.09	0.006
Steeper K (D)	49.55 ± 3.86	48.56 ±4.53	47.66 ± 4.32	< 0.001
Flattest K (D)	45.16 ± 2.62	44.68 ± 2.60	43.93 ± 3.44	< 0.001
Sphere (D)	−2.10 ± 2.16	−2.01 ± 2.43	−1.26 ± 2.75	0.008
Cylinder (D)	−3.57 ± 2.06	−2.79 ±2.16	−2.96 ± 2.00	0.100
Spherical equivalent (D)	−4.46 ± 3.50	−2.98 ± 3.02	−2.44 ±2.90	0.004
Thinnest pachy (um)	477.11 ± 31.19	462.78 ± 76.0	463.05±42.70	0.01

Note: *p value between pre and +10 postoperative for each variable.

Abbreviations: CXL, corneal collagen crosslinking; 1y, 1 year post CXL; +10y, postoperative follow up at 10 years or longer; K, keratometry; D, diopters; um, microns.

Table 2 Cases with Intense Keratometric Flattening Effect

Case	Age	UCVA Pre	UCVA Post	BCVA Pre	BCVA Post	Kmax Pre	Kmax Post	Steeper K Pre	Steeper K Post	Pachy TP Pre	Pachy TP Post	Procedure
1	14	1.30	0.70	0.40	0.04	55.3	49.2	52.8	47.2	485	441	CXL only
2	14	1.30	0.70	0.40	0.04	58.6	48.9	54.8	48.0	463	452	CXL only
3	37	1.30	1.00	0.30	0.18	52.6	43.4	48.8	38.8	488	355	CXL only
4	26	1.00	0.30	0.30	0.00	55.4	45.7	49.8	44.0	540	517	CXL only
5	22	2.00	1.30	0.18	0.10	60.1	55.1	54.9	52.5	429	431	CXL only
6	35	0.18	0.40	0.0	0.1	50.8	45.8	44.7	44.4	509	476	CXL only
7	24	1.00	2.00	0.18	1.30	–	44.1	47.1	35.6	512	415	CXL only

Abbreviations: Pre, preoperative evaluation; post, postoperative evaluation at 10 years or longer; UCVA, uncorrected visual acuity; BCVA, best-corrected visual acuity; K, keratometry; Kmax, maximum K; Ks, steeper K; Pachy, pachymetry; TP, thinnest point, CXL-PRK, CXL associated with photorefractive keratectomy.

Figure 1 Pre- and post-operative steeper keratometry (A), flatter keratometry (B) and Pre- and post-operative spherical equivalent (C).

Figure 2 Top: preoperative Scheimpflug analysis; Bottom: 13 years postoperative Scheimpflug analysis of the case presenting an extreme flattening of 11.5D in the steeper keratometry.

Figure 3 (A) Postoperative anterior segment optical coherence tomography of the case presenting an extreme flattening of 11.5D in the steeper keratometry; (B) Pentacam densitometric values of the same patient.

Table 3 Corneal Densitometry Measurements at 10 Years or More After CXL

Densitometry (GSU)	Anterior	Central	Posterior	Total
0–2 mm
Flattening Kmax ≥ 5 D	28.9 ± 9.69	18.0 ± 5.02	12.5 ± 4.11	19.3 ± 5.16
Flattening Kmax < 5 D	24.8 ± 6.86	15.3 ± 2.69	10.3 ± 1.75	16.8 ± 3.26
P value*	0.25	0.21	0.26	0.35
r	−0.30	−0.038	−0.22	−0.15
P value**	0.064	0.82	0.19	0.36
2–6 mm
Flattening Kmax ≥ 5 D	23.4 ± 5.38	14.5 ± 2.63	10.6 ± 1.38	16.2 ± 2.92
Flattening Kmax < 5 D	20.7 ± 4.22	13.0 ± 1.88	10.3 ± 1.40	14.7 ± 2.20
P value*	0.18	0.17	0.64	0.30
r	−0.24	−0.0013	−0.12	−0.11
P value**	0.14	0.99	0.47	0.51
6–10 mm
Flattening Kmax ≥ 5 D	18.5 ± 2.39	13.0 ± 1.57	11.0 ± 1.30	14.2 ± 1.53
Flattening Kmax < 5 D	19.6 ± 4.45	13.5 ± 2.82	11.5 ± 1.95	14.9 ± 2.95
P value*	0.97	0.94	0.55	0.88
r	−0.023	0.11	0.02	0.018
P value**	0.89	0.53	0.91	0.92
Total
Flattening Kmax ≥ 5 D	22.7 ± 2.83	14.7 ± 1.99	11.1 ± 1.58	16.2 ± 1.87
Flattening Kmax < 5 D	22.2 ± 4.21	14.4 ± 2.24	11.5 ± 1.52	16.0 ± 2.40
P value*	0.51	0.72	0.43	0.71
r	−0.17	0.037	0.05	−0.078
P value**	0.31	0.83	0.77	0.64

Abbreviations: CXL, corneal collagen crosslinking; GSU, grayscale units; Kmax, maximum keratometry; P value*, p value for Groups comparison using Wilcoxon sum range test; r, Spearman rank correlation coefficient between the densitometric value and the amount of keratometric flattening (expressed in negative values); p value**, from the Pearson correlation coefficient; D, Diopters.