The aim of this study is to investigate the clinical efficacy of epithelium-off versus transepithelial accelerated corneal collagen cross-linking (ACXL) in the treatment of advanced keratoconus.

Fifty-three keratoconus patients (61 eyes) who underwent ACXL were selected from August 2019 to October 2021 at laser Myopia Treatment Center of Xi′an First Hospital for retrospective study. Among them, there were 30 cases (32 eyes) male and 23 cases (29 eyes) female with the mean age of (24.3±6.9) years. Patients were divided into epithelium-off group (31 eyes) and transepithelial group (30 eyes) according to different ACXL operation types. The preoperative and postoperative at 3 months, 6 months, 12 months, 18 months, 24 months uncorrected visual acuity (UCVA), the best corrected visual acuity (BCVA), spherical equivalent (SE), the corneal astigmatism (CA), theanterior flat keratometry (K1), theanterior steep keratometry (K2), the maximal anterior keratometric power (Kmax), the posterior corneal curvature (PCC), and the thinnest corneal thickness (TCT) were performed and recorded the postoperative failure rate. UCVA, BCVA, TCT, K1, K2, Kmax, PCC, CA and SE were in accordance with normal distribution, and expressed as ±s and compared by independent sample t-test for intra groups before operation, multi-sample repeated measurement analysis of variance for inter-group, and repeated measurement analysis of variance for intra-group before and after treatment. The postoperative failure rate of the two cross-linking operations was expressed as eye number and percentage, and compared by Fisher′s exact test.

After surgery for 24 months, UVCA, BCVA, SE, CA, K1, K2, Kmax, PCC and TCT of patients in the epithelium-off group were (0.83±0.36) logarithmic minimum angle of resolution (logMAR), (0.20±0.15)logMAR, (-8.84±4.20)D, (-3.38±2.14)D, (44.85±1.74)D, (48.16±2.27)D, (49.86±10.51)D, (-6.89±0.48)D and (456.80±33.69)μm, respectively; those of patients in the transepithelial group were (1.01±0.46)logMAR, (0.33±0.66)logMAR, (-7.78±6.19)D, (-2.67±2.34)D, (46.63±3.40)D, (49.59±3.54)D, (55.92±7.69)D, (-7.15±0.55)D及(442.93±34.49)μm, respectively. There was no significant difference in the interaction of UVCA, BCVA, SE, CA, K1, K2, Kmax, PCC and TCT at different time point between the two groups (F_interaction=0.56, 0.80, 0.84, 0.32, 0.59, 1.70, 1.07, 0.31, 1.93; P>0.05). The difference in BCVA between the two groups was statistically significant (F_intra-group=4.27, P<0.05). There were significant differences in K2 at each time point in epithelium-off group (F=7.96, P<0.05). There were significant differences in Kmax at each time point in epithelium-off group (F_time=3.56, P<0.05). There were significant differences in TCT of epithelium-off group at each time point (F_time=7.72, P<0.05). After operation for one year, the failure rate of epithelium-off group and transepithelial group were 2 eyes (6.45%) and 6 eyes (20.00%), respectively, and there was no significant difference between them(P>0.05).

Long-term observation showed that epithelium-off CXL and transepithelial CXL are safe and effective in stabilizing keratoconus morphology and controlling keratoconus progression. In advanced keratoconus patients with the thinnest corneal thickness greater than 400 μm, epithelium-off CXL was superior to transepithelial CXL in controlling vision, corneal curvature and astigmatism.