Cross-linking of scleral collagen in the rabbit using riboflavin and UVA.
OBJECTIVE
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 x10 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+/-.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.
Wollensak
Gregor
G
Moscow Helmholtz Research Institute of Eye Diseases, Moscow, Russia. gwollens@hotmail.com
Iomdina
Elena
E
Dittert
Dag-Daniel
DD
Salamatina
Olga
O
Stoltenburg
Gisela
G
D000818:Animals; D001696:Biomechanical Phenomena; D003094:Collagen / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D003432:Cross-Linking Reagents; D005260:Female; D020287:In Situ Nick-End Labeling; D008854:Microscopy, Electron; D020419:Photoreceptor Cells, Vertebrate / Q000187:drug effects / Q000528:radiation effects / Q000648:ultrastructure; D017319:Photosensitizing Agents / Q000494:pharmacology* / Q000633:toxicity; D011817:Rabbits; D011833:Radiation Injuries, Experimental / Q000473:pathology; D012164:Retinal Diseases / Q000473:pathology; D012256:Riboflavin / Q000494:pharmacology* / Q000633:toxicity; D012590:Sclera / Q000187:drug effects* / Q000528:radiation effects*; D014466:Ultraviolet Rays / Q000009:adverse effects
D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin