Cross-linking of scleral collagen in the rabbit using riboflavin and UVA: Acta Ophthalmologica Scandinavica 2005

Purpose: Scleral biomechanical weakness and thinning is known to be one of the main factors in the pathogenesis of progressive myopia. We tried to strengthen rabbit sclera by cross-linking scleral collagen using ultraviolet A (UVA) and the photosensitizer riboflavin. Methods: Circumscribed 10 x 10 mm sectors of the posterior - equatorial sclera of six chinchilla rabbit eyes were treated in vivo using a UVA double diode with 4.2 mW/cm(2) UVA at 370 nm and applying 0.1% riboflavin-5-phosphate drops as photosensitizer for 30 min. 1 day postoperatively biomechanical stress-strain measurements of three treated scleral strips were performed using a microcomputer-controlled biomaterial testing device and compared to non-treated contralateral control sclera. In addition, three treated eyes were examined histologically by light microscopy, TUNEL staining and electron microscopy to evaluate side-effects. Results: Following the cross-linking treatment, the ultimate stress was 11.87 +/- 1.8 MPa versus 3.63 +/- 0.40 in the controls (increase of 227.9%, p = 0.014), Young's modulus 27.67 +/- 4.16 MPa versus 4.9 +/- 2.15 MPa in the controls (increase of 464.7%, p=0.021) and ultimate strain 92.2 +/- 7.43% versus 165.63 +/- 19.09% in the controls (decrease of 54.52%, p=0.012). Histologically, serious side-effects were found in the entire posterior globe with almost complete loss of the photoreceptors, the outer nuclear layer and the retinal pigment epithelium (RPE). Conclusions: Our new method of scleral collagen cross-linking proved very effective in increasing the scleral mechanical strength; the new treatment may represent an option for strengthening scleral tissue in progressive myopia. However, serious side-effects were observed in the outer retina. In future studies these side-effects could be avoided by reducing the irradiation dose below the cytotoxic level of the retina. Before its clinical application, the new method should be tested in a myopia animal model.