• progressive myopia;
  • sclera;
  • UVA;
  • riboflavin;
  • collagen cross-linking;
  • Young's modulus


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 × 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/cm2 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.