All subjects in the present study were recruited from patients who underwent ATE-CXL at Eye and ENT Hospital of Fudan University in Shanghai, China. Criteria for inclusion were age = 10–17 years, progressive keratoconus (≥1.00 D increase in maximal keratometry in the last year, or ≥1.00 D increase in astigmatic degree in the last year), minimal corneal thickness ≥ 400 μm. Exclusion criteria were a history of ocular disease (except keratoconus), previous ocular surgeries, and a history of systemic diseases. Finally, 18 eyes of 17 patients (male:female = 15:2) with a mean age of 14.44 ± 1.98 years were enrolled in this study. The mean spherical error of all the subjects was − 4.17 ± 3.88 D. The mean cylindrical error was − 3.35 ± 2.44 D, and the mean spherical equivalent refraction was − 5.84 ± 4.13 D. Every patient underwent a 1-year follow-up after the operation.
This study adhered to the tenets of the Declaration of Helsinki and was approved by the Ethics Committee of the Eye and ENT Hospital of Fudan University in Shanghai, China. Written informed consent was obtained from at least one parent or legal guardian of each subject after a detailed explanation of the procedure, and all the procedures were carried out with the subjects’ consent.
All patients underwent slit-lamp biomicroscope examination, best corrected visual acuity (BCVA) and manifest refraction assessment, preoperatively and at 1, 6, and 12 months postoperatively. Steepest meridian keratometry (K1), flattest meridian keratometry (K2), maximum keratometry (Kmax), and thinnest corneal thickness (TCT) were measured by the Pentacam imaging system (Oculus GmbH, Wetzlar, Germany) before the treatment and at each follow-up time point.
Posterior elevation data for the cornea were also obtained by the Pentacam software. The reference best-fit sphere (BFS) was defined in the central 8-mm region of the cornea, which was set to be the same across the images from each patient. Posterior central elevation (PCE) and posterior mean elevation (PME) were measured in the central 4-mm area above the BFS. The change in the posterior elevation (ΔPCE and ΔPME) was found by subtracting preoperative data from postoperative data for each patient.
All surgeries were performed by the same surgeon. Before the surgery, topical anesthetic eye drops were applied. After a lid speculum was used, a trephine (Model 52503B; 66 vision Tech Co, Ltd., Suzhou, China) was placed in the center of the cornea. ParaCel Solution (0.25% riboflavin-5-phosphate, hydroxylpropyl methylcellulose, NaCl, ethylenediaminetetraaceticacid, Tris, and benzalkonium chloride; Medio-Haus-Medizinprodukte GmbH, Kiel, Germany) was dripped into the trephine to cover the corneal epithelium for 4 min. The cornea was then continually infiltrated with Vibex-Xtra Solution (riboflavin phosphate 2.80 mg/mL and NaCl, Avedro, Inc.) for 6 min. After the cornea was rinsed with balanced salt solution (BBS), UV treatment was administered using Avedro’s KXL System (Avedro, Inc) for 5 min and 20 s with 365-nm UV-A light and 45 mW/cm2 irradiation in the pulsed mode (one second on, next second off). BBS was used to keep the ocular surface moist during irradiation. A bandage contact lens was applied after the procedure. Postoperative medications included levofloxacin (4 times daily for 1 week), 0.1% fluorometholone (7 times daily initially, then gradually reduced for 3 weeks), and artificial tears (4 times daily for 4 weeks).
Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS, Inc., Armonk, NY). Continuous parameters were described as mean ± standard deviation. Repeated measures analysis of variance (ANOVA) with Bonferroni-adjusted post hoc comparisons and Friedman rank test were performed to evaluate the significance of differences between preoperative and postoperative data. A P value less than 0.05 was considered statistically significant.