Evaluation of the Safety and Long-term Scleral Biomechanical Stability of UVA Cross-linking on Scleral Collagen in Rhesus Monkeys

PURPOSE: To investigate the changes of retinal and choroidal parameters, scleral biomechanical strength, and ocular histopathology after scleral ultraviolet-A (UVA) cross-linking (CXL) in rhesus monkeys eyes, and to evaluate the safety and long-term biomechanical stability of scleral CXL for preventing myopia from progressing further in clinic. METHODS: Six 3-year-old male rhesus monkeys (12 eyes) were randomized to receive UVA-CXL procedures applied on the superotemporal equatorial sclera. Optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) were used for examination before and 1 week and 1, 3, 6, and 12 months after CXL. The stress-strain behaviors of equatorial scleral strips were analyzed 12 months postoperatively by a biomaterial tester. Hematoxylin–eosin and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining were performed 12 months postoperatively. RESULTS: For central retinal thickness, choroidal thickness, and flow density of central retinal superficial vascular networks, no statistical difference was noted between CXL eyes and control eyes at 12 months postoperatively ( P > .05). The biomechanical stability of sclera was increased. The scleral stress and Young modulus at 8% strain corresponded to 184% and 183%, respectively, of the control values at 12 months (each P < .001). No retinal damage was detected on histology in scleral CXL eyes. There was no obvious difference between scleral CXL eyes and control eyes by hematoxylin–eosin and TUNEL staining ( P > .05). CONCLUSIONS: Scleral CXL with riboflavin/UVA in rhesus monkey eyes could strengthen the biomechanical properties of scleral tissues and maintain the stability for 12 months postoperatively. The UVA-CXL on the sclera of rhesus monkey eyes seems to be effective and safe. [ J Refract Surg . 2020;36(10):696–702.]