This was a prospective self-controlled study. Eighteen patients (18 eyes) were recruited in this study from the Department of Ophthalmology of Fudan University EENT Hospital. The eyes enrolled were diagnosed with keratoconus and kept stable for 12 months. Stability of keratoconus was defined as less than 0.5 diopter(D) increase in maximum keratometry, manifest cylinder, or manifest refraction spherical equivalent, or no loss or loss of one line of corrected distance visual acuity over the previous 12 months. The diagnosis of keratoconus was based on corneal topography data and stromal thinning.
Inclusion criteria were the following: patients aged at least 18 years ;
CDVA of 20/80 or better; SE 0 to -3.00 D; minimal corneal thickness 475 micron or better; clear cornea without visible scar on slit-lamp examination.
Exclusion criteria were the following: previous ocular trauma or surgery; other ocular disease or systemic disease that may affect the cornea; taking Vitamin C (ascorbic acid) supplements within 1 week of the cross-linking treatment.
The Amsler–Krumeich (AK) classification of keratoconus was used in this study. Mean central K readings of less than 48.0 diopters (D) in addition to eccentric steepening and mild myopia and astigmatism indicate stage 1 disease. Stage II disease has mean central K readings less than 53.00 D and increasing myopia and astigmatism with the absence of scarring. Stage III disease has mean central K readings of greater than 53.00 D, myopia, and astigmatism from 8.00 to 10.00 D and minimum corneal thickness of 300 to 400 mm. Finally, stage IV disease is indicated by central corneal scarring with mean central K readings greater than 55.00 D with immeasurable refractions.
Routine preoperative examinations were performed to exclude patients with contraindications. All patients fully understood the procedure and signed informed consent. This study was approved by the Ethical Committee of Fudan University EENT Hospital Review Board and followed the tenets of the Helsinki declaration.
In each visit, the following parameters were assessed: corrected distance visual acuity (CDVA), slit- lamp biomicroscopy, corneal topography, optical tomography and pachymetry with the Pentacam (Oculus, Germany) and endothelial biomicroscopy (NIDEK, Japan). All post- operative complications were recorded.
All operations were performed by the same surgeon (ZXT). After topical anesthesia with 4% oxybuprocaine, 0.1% riboflavin (ParaCel, Avedro Inc.) was applied to the cornea for 4 minutes, after which 0.25% riboflavin (VibeX xtra, Avedro Inc.) was applied for 6 minutes. The cornea was irradiated with UVA light at 45 mW/cm2 and pulsed illuminated. Total UVA dose was 5.4J when the corneal curvature was no more than 48D, 10J when it was 48D-51D, and 15J when it was larger than 51D. The irradiation time and shape were calculated by the KXL II system (Avedro Inc., USA) using corneal topography data(Fig.1). At the end of operation, a bandage contact lens (ACUVE OASYS, Johnson & Johnson Inc.) was placed over the cornea.
The post-operative topical medication regimens were identical for each eye: 0.3% levofloxacin 4 times per day for 3 days, a 0.1% fluorometholone solution tapered from 6 times per day to 1 time per day over the course of 18 days, and a preservative-free tear supplement 4 times per day for 1 month. The contact lens was removed on day 1 post-operation.
The patients were followed up at 1 day, 1 month, 3 months, 6 months and 1 year post-operatively. The examinations included UDVA, CDVA, endothelial cell density and Pentacam corneal topography to get values of flat K (K1), steep K (K2), mean K (Km), and maximum K (Kmax).
Data are expressed as the mean ± standard deviation (SD). The P-value was determined using single-factor repeated measures ANOVA. A P value<0.05 was considered statistically significant. All statistical analyses were performed using SPSS software (version 16.0, SPSS Inc., Chicago, IL).