Scleral cross-linking by riboflavin and blue light application in young rabbits: damage threshold and eye growth inhibition.

BACKGROUND: Scleral cross-linking (SXL) by riboflavin and light application has been introduced as a possible treatment to increase scleral tissue stiffness and to inhibit excessive axial elongation of highly myopic eyes. We evaluated an ocular tissue damage threshold for blue light irradiation, and used SXL treatment to induce eye growth inhibition. METHODS: The sclera of 3-week-old rabbits (39 pigmented and 15 albino rabbits) were treated with different blue light intensities (450 ± 50 nm) and riboflavin. Alterations and a damage threshold were detected in ocular tissues by means of light microscopy and immunohistochemistry. The influence of SXL on the eye growth was examined in 21 young rabbits and was measured by using A-scan ultrasonography, micrometer caliper, and for selected eyes additionally by MR imaging. RESULTS: Light microscopic examinations demonstrated degenerative changes in ocular tissue after irradiation with blue light intensities above 400 mW/cm(2) (with and without riboflavin application). Therefore, that light intensity was defined as the damage threshold. Tissue alteration in retina, choroid, and sclera and activation of retinal microglia cells and Müller cells could be earlier observed at blue light intensities of 150 and 200 mW/cm(2). Albino rabbits were less sensitive to this SXL treatment. A significant reduction of the eye growth could be detected by SXL treatment with the minimal efficient blue light intensity of 15 mW/cm(2) and maintained stable for 24 weeks. CONCLUSIONS: SXL with riboflavin and blue light intensities below a defined damage threshold can induce a long lasting growth inhibitory effect on young rabbit eyes. Therefore, SXL might be a realistic approach to inhibit eye elongation in highly myopic eyes.

Dose-dependent collagen cross-linking of rabbit scleral tissue by blue light and riboflavin treatment probed by dynamic shear rheology.

PURPOSE: To determine the visco-elastic properties of isolated rabbit scleral tissue and dose-dependent biomechanical and morphological changes after collagen cross-linking by riboflavin/blue light treatment. MATERIAL: Scleral patches from 87 adult albino rabbit eyes were examined by dynamic shear rheology. Scleral patches were treated by riboflavin and different intensities of blue light (450 nm), and the impact on the visco-elastic properties was determined by various rheological test regimes. The relative elastic modulus was calculated from non-treated and corresponding treated scleral patches, and treatments with different blue light intensities were compared. RESULTS: Shear rheology enables us to study the material properties of scleral tissue within physiological relevant parameters. Cross-linking treatment increased the viscous as well as the elastic modulus and changed the ratio of the elastic versus viscous proportion in scleral tissue. Constant riboflavin application combined with different blue light intensities from 12 mW/cm(2) up to 100 mW/cm(2) increased the relative elastic modulus of scleral tissue by factors up to 1.8. Further enhancement of the applied light intensity caused a decline of the relative elastic modulus. This might be due to destructive changes of the collagen bundle structure at larger light intensities, as observed by histological examination. CONCLUSION: Collagen cross-linking by riboflavin/blue light application increases the biomechanical stiffness of the sclera in a dose-dependent manner up to certain light intensities. Therefore, this treatment might be a suitable therapeutic approach to stabilize the biomechanical properties of scleral tissue in cases of pathological eye expansion.