Impact of accelerated corneal cross-linking on endothelial cell density and morphology in central and paracentral regions after six months

Background. Keratoconus (KC) is a progressive ectatic corneal disease (ECD) involving conical bulging and thinning of the corneal stroma due to a biomechanical weakening of the tissue. Corneal collagen cross-linking (CXL) is the only procedure to halt the progression of KC. During CXL, the strongest radiation effect is targeted at the anterior 300 µm of corneal thickness and should not penetrate deeper. Nevertheless, the risk of UVA exposure to the endothelium remains. Aim. To compare the endothelial cell density and morphology in the central and paracentral points of the cornea before and six months after accelerated CXL. Methods. This study evaluated 22 eyes of 20 adult patients who underwent accelerated CXL using a protocol of 9 mW/cm² for 10 minutes to treat progressive KC at the Department of Ophthalmology, Hospital of the Lithuanian University of Health Sciences, between 2021 and 2024. Endothelial cell density (ECD), the coefficient of variation in cell size (CV), and the percentage of hexagonal cells (HEX) were quantitatively assessed preoperatively and at six months postoperatively at both central and paracentral corneal regions using a non-contact specular microscope (NIDEK, USA; CEM-530). Statistical analyses were performed using IBM SPSS Statistics 26.0, with descriptive methods and the Wilcoxon signed-rank test. p-values less than 0.05 were considered statistically significant. Results. The mean age of KC patients was 27.15 ± 6.976 years. Sixteen cases were males (80%) and four cases were females (20%). There was a statistically significant increase in CV at six months postoperatively at each paracentral location (0°, p = 0.02; 90°, p = 0.003; 180°, p = 0.009; 270°, p = 0.032). Additionally, a statistically significant reduction in HEX was observed at both the central (p = 0.016) and paracentral points (90°, p = 0.013; 180°, p = 0.017) at six months postoperatively. Furthermore, a statistically significant decline in ECD was noted at the 0° paracentral location (p = 0.016). Conclusion. The use of accelerated CXL may have a negative impact on corneal endothelial parameters at central and paracentral locations after six months. Further studies with larger sample sizes and longer follow-up periods are necessary.