Purpose  To evaluate the efficiency of the UVA-riboflavin cross-linking method on sclera thinning disorders by investigating the dynamic biomechanical changes of rabbit sclera after cross-linking.
Methods  Twenty New Zealand White rabbits weighing 2.5-3.0kg were used. They was randomly divided into two groups, 10 in the control group(Group A) and 10 in the cross-linking group(Group B). After general and local anesthesia, only the right eye of each rabbit was treated. The conjunctiva was incised, and the equatorial sclera of the upper nasal quadrant was exposed. 0.1% riboflavin-5-phosphate saline solution was dropped onto the equatorial sclera 5 min before the irradiation and every 5 min during the irradiation. UVA irradiation(370 nm, 3mw/cm², 30min, 5.4 J/cm²) was applied in Group B, but not in Group A. After irradiation, chloramphenicol solution was applied and the conjunctiva closed using a 7-0 thread. Then, the animals were randomly divided into 2 subsets depending on the postoperative time interval of either 1 week or 1 month, respectively: 1. At one week after surgery, ten rabbits(5 in Group A and 5 in Group B) were sacrificed under general anesthesia, and biomechanical stress-strain measurements were performed for the treated scleral specimens. The sclera strips(2×10mm) were clamped vertically between the jaws of the microcomputer-controlled biomaterial tester. Strain was increased linearly with a velocity of 1 mm/min and stress was measured up to tissue rupture. The parameters ultimate stress(MPa) and ultimate strain(%) of the samples were used for analysis. Young’s modulus(MPa) was determined as the slope of the stress-strain graph at 50% strain. 2. At one month after surgery, ten rabbits(5 in Group A and 5 in Group B) were killed and performed the biomechanical measurement in the same way. The parameters ultimate stress(MPa), ultimate strain(%) and Young’s modulus(MPa)of the scleral samples were compared between the data at 1 week and 1 month.
Results  1. After cross-linking treatment, the ultimate stress of the scleral strips was increased by 254.1% in one week and 189.5% in one month(p＜0.05). 2. The ultimate strain decrease of the scleral strips was 79.1% in one week after the cross-linking, and 82.3 % in one month(p＜0.05). 3. Young’s modulus of the sclera was increased by 321.5% in one week and 230.0% in one month(p＜0.05).
Conclusion  UVA-riboflavin cross-linking increased the biomechanical rigidity of rabbit sclera obviously at one month after surgery, and it may be an effective method on sclera thinning disorders.