The Evaluation of Ultraviolet A/Riboflavin Corneal Crosslinking on Keratoconic Patients with a Corneal Thickness Less than 400 μm: A 3-Year Follow-Up

Abstract

Objective: To evaluate the effect of ultraviolet A/riboflavin corneal crosslinking (CXL) on keratoconic patients with a corneal thickness less than 400 μm. Methods: In this prospective study, patients with keratoconus were divided into a thin cornea group with a corneal thickness (CT) less than 400 μm and a thick cornea group with a CT more than 400 μm. The patients in the thin and thick cornea groups were treated with a hypotonic or isotonic riboflavin solution before and during CXL. Corneal morphological parameters were evaluated before and after CXL during a 3-year follow-up. The data were analyzed with a repeated measures ANOVA, t test, Wilcoxon rank sum test or Mann-Whitney U test. Results: After surgery, the maximum keratometry (Kmax) of the thin and thick cornea groups underwent a continuous decrease (F= 24.364, P<0.001; F=10.427, P=0.001). In the thin group, the Kmax value was 60.51±6.11 diopters (D) before surgery and significantly decreased to 57.43±6.82 D, 56.13±6.85 D and 54.97±6.66 D at 1, 2 and 3 years after surgery (t=3.670, P=0.002; t=4.637, P<0.001; t=5.816, P<0.001). In the thick group, the Kmax value was 54.56±6.27 D before surgery and significantly decreased to 53.25±6.42 D, 52.32±6.47 D and 51.58±6.70 D at 1, 2 and 3 years after surgery (t=2.266, P=0.040; t=3.302, P=0.005; t=3.769, P=0.002). The Kmax value of the thin cornea group before surgery was higher than that of the thick cornea group (t=2.714, P=0.011). There were no significant differences in Kmax between the two groups at 1 year, 2 years or 3 years. In the thin group, there were significant differences between the preoperative and 3-year postoperative visual acuity (UCVA), best corrected visual acuity (BCVA) and thinnest corneal thickness (TCT) (Z=-2.716, P=0.007; Z=-3.063, P=0.002; t=4.468, P<0.001). In the thick group, there were significant differences between the preoperative and 3-year postoperative UCVA, BCVA and TCT (t=3.572, P=0.003; Z=-2.956, P=0.003; Z=-3.410, P=0.001). In the two groups, there were no significant differences between the preoperative and 3-year postoperative intraocular pressure (IOP) or endothelial cell density (ECD). There were no significant differences in pre- or postoperative UCVA, BCVA, IOP, or ECD between the two groups. There were significiant differences in pre- and postoperative TCT between the two groups (Z=-4.816, P=0.001; Z=-4.024, P<0.001). Conclusion: CXL is an effective and safe way to halt disease progression and improve visual acuity in keratoconic patients with a CT less than 400 μm. Key words: keratoconus; ultraviolet A/riboflavin corneal crosslinking; hypotonic riboflavin solution; isotonic riboflavin solution; corneal thickness