The ultrastructure of rabbit sclera after scleral crosslinking with riboflavin and blue light of different intensities.
OBJECTIVE
We aimed to determine the ultrastructural changes of collagen fibrils and cells in the rabbit sclera after scleral crosslinking using riboflavin and blue light of different intensities. Scleral crosslinking is known to increase scleral stiffness and may inhibit the axial elongation of progressive myopic eyes.


METHODS
The equatorial parts of the sclera of one eye of six adult albino rabbits were treated with topical riboflavin solution (0.5 %) followed by irradiation with blue light (200, 400, 650 mW/cm(2)) for 20 min. After 3 weeks, the ultrastructure of scleral cells and the abundance of small- (10-100 nm) and large-diameter (>100 nm) collagen fibrils in fibril bundles of different scleral layers were examined with electron microscopy.


RESULTS
In the scleral stroma of control eyes, the thickness of collagen fibrils showed a bimodal distribution. The abundance of small-diameter collagen fibrils decreased from the inner towards the outer sclera, while the amount of large-diameter fibrils and the scleral collagen content did not differ between different stroma layers. Treatment with riboflavin and blue light at 200 mW/cm(2) did not induce ultrastructural changes of cells and collagen fibrils in the scleral stroma. Treatment with blue light of higher intensities induced scleral cell activation in a scleral layer-dependent manner. In addition, outer scleral layers contained phagocytes that engulfed collagen fibrils and erythrocytes. Blue light of the highest intensity induced a reduction of the scleral collagen content, a decreased abundance of large-diameter collagen fibrils, and an increased amount of small-diameter fibrils in the whole scleral stroma.


CONCLUSIONS
The data indicate that in rabbits, scleral crosslinking with riboflavin and blue light of 200 mW/cm(2) for 20 min is relatively safe and does not induce ultrastructural alterations of scleral cells and of the collagen composition of the scleral stroma. Irradiation with blue light of intensities between 200 and 400 mW/cm(2) induces scleral cell activation, which may contribute to scleral scarring and stiffening. Higher intensities cause scleritis.
Translational Center for Regenerative Medicine, University of Leipzig, Leipzig, Germany. Anett.Karl@medizin.uni-leipzig.de.|Paul-Flechsig-Institute for Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany. Anett.Karl@medizin.uni-leipzig.de.|Carl-Ludwig-Institute for Physiology, University of Leipzig, Liebigstr. 27a, 04103, Leipzig, Germany. Anett.Karl@medizin.uni-leipzig.de.
Anett
A
Karl
Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia.
Felix N
FN
Makarov
Translational Center for Regenerative Medicine, University of Leipzig, Leipzig, Germany.|Department of Ophthalmology and Eye Hospital, Medical Faculty, University of Leipzig, Leipzig, Germany.
Christian
C
Koch
Translational Center for Regenerative Medicine, University of Leipzig, Leipzig, Germany.|Paul-Flechsig-Institute for Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany.
Nicole
N
Körber
Translational Center for Regenerative Medicine, University of Leipzig, Leipzig, Germany.|Institute of Experimental Physics I, Faculty of Physics and Earth Sciences, University of Leipzig, Leipzig, Germany.
Carsten
C
Schuldt
Institute of Anatomy, Medical Faculty, University of Leipzig, Leipzig, Germany.
Martin
M
Krüger
Paul-Flechsig-Institute for Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany.
Andreas
A
Reichenbach
Department of Ophthalmology and Eye Hospital, Medical Faculty, University of Leipzig, Leipzig, Germany.
Peter
P
Wiedemann
Department of Ophthalmology and Eye Hospital, Medical Faculty, University of Leipzig, Leipzig, Germany.
Andreas
A
Bringmann
Department of Ophthalmology and Eye Hospital, Medical Faculty, University of Leipzig, Leipzig, Germany.|Limmat Eye Center, Zürich, Switzerland.
Hans Peter
HP
Iseli
Translational Center for Regenerative Medicine, University of Leipzig, Leipzig, Germany.|Paul-Flechsig-Institute for Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany.
Mike
M
Francke
D000818:Animals; D001696:Biomechanical Phenomena; D003094:Collagen / Q000494:pharmacology*; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004195:Disease Models, Animal; D008027:Light; D008854:Microscopy, Electron; D009216:Myopia / Q000503:physiopathology / Q000628:therapy*; D017319:Photosensitizing Agents / Q000494:pharmacology; D011817:Rabbits; D012256:Riboflavin / Q000494:pharmacology*; D012590:Sclera / Q000187:drug effects / Q000503:physiopathology / Q000648:ultrastructure*
D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin
Blue light; Collagen; Fibroblast; Rabbit; Sclera; Scleral crosslinking