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Effect of Ribolfavin-ultraviolet a Cross-linking on Corneal Collagen Ifbres Remodeling and Biomechanical Stability

Author: LiGang
Tutor: PengXiuJun
School: PLA Postgraduate Medical School
Course: Ophthalmology
Keywords: corneal collagen cross-linking biomechanics keratoconus
CLC: R779.6
Type: PhD thesis
Year: 2012
Downloads: 95
Quote: 1
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Abstract


Objective To evaluate the change of corneal keratocytes and collagens afterriboflavin-ultraviolet-A induced corneal collagen cross-linking (CXL) on rabbit’seyes, and investigate the role of collagen fibers remodeling in biomechanicalstability after CXL.The efficacy and safety of CXL in the management ofprogressive keratoconus were analyzed.Methods1Fifteen healthy New Zealand rabbits were divided into threegroups.CXL was performed on the right eye,all the left eyes were used as normalcontol. The eyes were enucleated and prepared for light microscopy examinationin1day,7days and4weeks after CXL. HE, α-smooth muscle actin and TUNELwere analyzed by histological staining.2Picrosirius-polarization and stress-straintest were performed on corneal specimens to analyze the qualitative change ofcollagens, peak load, peak stress and elastic modulus.3Corneal collagencrosslinking was performed in twenty-two eyes of13patients with progressivekeratoconus. Visual acuity, corneal topography, in vivo confocal microscopy, andendothelial cell count were evaluated at baseline and at1,3,6, and12monthsfollow-up.Results1Light microscope demonstrated that the corneal stroma collagenfibrils were tightly packed connective tissue,the keratocytes enmeshed in it.At thefirst day after CXL, scattered keratocytes were present in the stroma. There weremany apoptotic cells of epithelium and keratocytes. By day7, stromalkeratocyte’s edema regressed.The amount of apoptotic cells were less than thoseof epithelium and stroma at the first day after CXL. By week4, the cornealthickness restore the normal structure,the amount of apoptotic cells were scarce.By day7and week4, positve α-smooth muscle actin staining keratocytes werepresent.2.Red stained type I collagen was present in the stroma evenly and greenstained type III was dispersed in the stroma. By day7, the amount of type IIIcollagen increased and the fiber diameter became thickness and asymmetry. By week4, the amount of type III collagen still increased and was intermingled withtype I collagen in the stroma. After CXL the corneal elastic modulus increasedsignificantly compared with normal cornea. By day1, corneal elastic modulus invertical meridian was significant increased than that in horizontal direction.3.Mean uncorrected visual acuity(UCVA) and best spectacle-corrected visualacuity(BSCVA) increased0.115±0.158LogMAR and0.114±0.218LogMAR12months postoperatively respectively. Interim analysis of treated eyes showed aflattening of the steepest simulated keratometry value (K-max) and astigmatismby an average of1.893±3.713diopters (D) and0.117±1.488D respectively at12months. Central corneal thickness decreased by27.5±26.8μm and1.54±19.4μm atone month and12months postoperatively respectively.Intraocular pressure，endothelial cell count, lens and fundus didn’t change significantly at12monthsfollow-up.Conclusions1. The stromal keratocytes of the rabbit cornea werecharacterized by apoptosis after CXL and keratocytes repopulated from theperipheral stroma during restore phase.New proliferated keratocytes weremyofibroblasts which participated in collagen fibres remodeling.2. The ratio oftypes III/I collagen and distribution were significantly changed after CXL, whichindicated collagen fibres remodeling happened and the increased long-termbiomechanical stability was associated with this remodeling.3. CXL stabilisedand improved the UCVA and BSCVA as well as the maximum k-readings at1year postoperatively in our cohort. It seems to be a safe and promising procedureto stop the progression of keratoconus.

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