This retrospective study included 20 patients (33 eyes) diagnosed with KC at the Department of Ophthalmology, Peking Union Medical College Hospital, Beijing, China between July 2016 and November 2019. The study protocol followed the guidelines of the Declaration of Helsinki and the Institutional Review Board for Human Studies and was approved by the Peking Union Medical College Hospital Institutional Ethics Committee. Written informed consent was obtained from all the patients or a parent or guardian on behalf of any participants under the age of 18 before the study was initiated.
Preoperative and postoperative examinations included a slit-lamp examination, best spectacle-corrected visual acuity with and without a pinhole, uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) using a Snellen chart, corneal topography (TMS-4N; TOMEY, Erlangen, Germany), dual Scheimpflug Imaging System (Gallilei; Ziemer Ophthalmology, Port, Switzerland), and ultrasonic pachymetry (TOMEY Ltd, Aichi, Japan) of the central cornea. Goldmann applanation tonometry and an Ocular Response Analyzer (Reichert Technologies; Depew, New York, USA) were used to measure intraocular pressure and corneal biomechanical properties. The corneal demarcation line and the corneal epithelial and stromal thicknesses were measured and evaluated using anterior segment optical coherence tomography (AS-OCT) (Optovue RTVue XR, Optovue; Fremont, California, USA). Corneal epithelial and stromal thickness profiles were obtained at the thinnest part of the central cornea using 16 peripheral measurements on the corneal vertex; measurements and statistical analyses for the central 6-mm zone of corneal apex (inner areas, 3 mm of corneal apex; outer areas, 6 mm of corneal apex) were performed and measured [8]. For ultrasound pachymetry, the average measurements of the corneal thickness values were chosen (each single measurement represented the mean of five consecutive measurements).
Inclusion criteria for the study were as follows: documented progressive KC, patient age > 10 years, corneal thickness ≥ 400 µm, no other ocular pathologic signs (such as ocular surface infection or allergy), and no pregnancy or lactation. KC stage was determined according to the Amsler-Krumeich classification preoperatively.[1]
All patients underwent uneventful epi-off continuous accelerated CXL treatment with the use of a new high-intensity ultraviolet-A (UVA) illuminator (CCL-365; Peschke Meditrade GmbH; Huenenberg, Switzerland). All of the patients’ eyes underwent continuous (4 min) light illumination with an irradiation of 30 mW/cm2.
Surgical technique
All procedures were performed by one experienced surgeon (Y.L.) using a high-intensity UVA illuminator (KXL I, Avedro; Waltham, Massachusetts, USA) under sterile conditions. After topical anaesthesia with 0.5% proparacaine (Alcaine, Alcon-Couvreur; Puurs-Sint-Amands, Belgium, USP), the corneal epithelium was mechanically removed with an 8.0–9.0 mm diameter cut using a crescent knife. After epithelial removal, a solution of 0.1% riboflavin and 1% hydroxypropyl methylcellulose (Vibex Rapid, Avedro) was instilled on the centre of the cornea and was allowed to soak for 10 min. After completing the riboflavin soak, the solution was rinsed from the eye with a balanced salt solution. Next, UVA energy was applied at 7.2 J/cm2 with an irradiance of 30 mW/cm2 to the eye underwent continuous (4 min) light illumination for epi-off continuous accelerated CXL. Finally, the eye was rinsed with a balanced salt solution again, and a bandage contact lens (PureVision; Bausch & Lomb, Rochester, New York, USA) was applied to the cornea until complete re-epithelialisation was achieved.
After surgery, all patients were administered with topical 0.5% levofloxacin four times daily for 2 weeks, 0.5% corticosteroid loteprednol etabonate (Lotemax; Bausch & Lomb, Tampa, Florida, USA) and preservative-free artificial tears four times daily for one month, and 0.2% carbomer eye gel (Liposic; Bausch & Lomb, Brunsbütteler Damm, Berlin, Germany) once daily at night for one month.
Patients were examined before surgery and at 3, 6, and 12 months postoperatively. Postoperative evaluation included UDVA, corneal biomechanical parameters, corneal topography, and corneal thickness profiles (epithelial and stromal) using AS-OCT.
Statistical analysis
Data were recorded into a Microsoft Excel spreadsheet (Microsoft; Redmond, Washington, USA), and statistical analysis was performed using SPSS for MAC, version 25.0 (IBM SPSS, Armonk, New York, USA). The normality of the data was tested with the Shapiro-Wilk test. A paired t-test was performed to analyse postoperative changes. If the data were not normally distributed, the Wilcoxon rank-sum test was performed. Friedman analysis of variance (ANOVA) with the Bonferroni correction was applied in case data did not show normal distribution. P values less than 0.05 were considered statistically significant.