The Experimental Studies Of Riboflavin/Uva Cross-Linking In Sclera

In1998, Spoerl et al. found that some methods could change the corneal biomechanical behavior, and in this study treatment with riboflavin and UV-irradiation as well as weak glutaraldehyde or Karnovsky’s solutions could result in an increased stiffness of the cornea. Through many of experiment studies on the cross-linking, in2003the riboflavin/UVA cross-linking was applied in treating keratoconus in clinical. Wollensak et al. found that70%eyes regression with a reduction of the maximal keratometry readings by2.01diopters and of the refractive error by1.14diopters. Visual acuity improved in65%eyes. And corneal and lens transparency, endothelial cell density, and intraocular pressure remained unchanged.Keratoconus is a noninflammatory disease in which the cornea thins and becomes cone-shaped, distorting the shape of the eye as well as interfering with vision. Riboflavin/UVA mediated corneal collagen cross-linking can improve the cornea biomechanical properties through enhancing the crosslink among the corneal collagen fibers. Cross-linking can be applied to increase scleral rigidity in patients with progressive myopia, where thinning processes also occur in the sclera of progressive myopia. Through applying different collagen cross-linking methods to the porcine and human sclera, Wollensak and Spoerl found that collagen cross-linking induced by riboflavin-UVA led to a significant increase in biomechanical strength in human and porcine sclera. The researches about sclera riboflavin/UVA cross-linking is poorer than corneal cross-linking, and the parameters about the method in sclera was referred to cornea. The difference of microstructure is obviously between sclera and cornea. So the appropriate riboflavin/UVA cross-linking parameters in cornea may not be suitable for sclera. Therefore, the first part of present study is designed to investigate the optimal duration of irradiation when administering surface irradiance is3mW/cm2in vivo rabbit model. And the purpose of the second part of my study is to compare the biomechanical properties of porcine, rabbit, and human sclera both before and after riboflavin/UVA cross-linking in the parameters of the first part, then to assess which tissue is closer to human sclera in biomechanical behavior under the same conditions. Because of extremely limited availability, porcine and rabbit sclera are often used as models for human sclera tissue.Part I:Effect of irradiation time on riboflavin/UVA cross-linking in rabbit scleraPURPOSE:To investigate the effect of the duration of irradiation on the biomechanical parameters of combined riboflavin/ultraviolet-A (UVA) cross-linking in rabbit sclera.SETTING:Department of Ophthalmology, Shandong Provincial Hospital affiliated to Shandong University. DESIGN:Animal eye study.METHODS:For this study,36New Zealand rabbits were divided into6groups based on the duration of irradiation (10,20,30,40,50or60minutes). After the application of0.1%riboflavin drops (without dextran) which was a photosensitizer, the animals were irradiated, with 3mW/cm2UVA at365nm. Only the left eye of each rabbit was treated. The right eyes were served as controls. All the animals were euthanized24hours postoperatively. One eye from each treated group was used for light microscopy. The other treated eye and all control eyes were prepared for biomechanical testing. The biomechanical parameters examined were ultimate stress, Young’s modulus, and the physiological modulus.RESULTS:1、The eyes irradiated for10or20minutes did not differ significantly from the control eyes(p>0.05).2、Stress-strain measurement of scleral strips irradiated for≥40minutes revealed a significant increase in the ultimate stress, Young’s modulus, and the physiological modulus (p<0.05).3、There was a significant increase in the physiological modulus of scleral strips irradiated for≥30minutes (p<0.05).4、All irradiated regions showed inflammation reaction. Eyes that were irradiated≤40minutes without exhibiting retinal damage. Eyes that were irradiated for50and60minutes exhibited retinal damage.CONCLUSIONS:1、Riboflavin/UVA cross-linking can lead to a noticeable increase in the biomechanical stiffness of the sclera.2、The physiological modulus is the most sensitive tool to measure stiffness.3、The optimal duration of irradiation is40minutes.Part Ⅱ:Comparison of Riboflavin/UVA Cross-Linking in Porcine, Rabbit, and Human ScleraPURPOSE:To compare the biomechanical properties of porcine, rabbit, and human sclera before and after riboflavin/ultraviolet A (UVA) cross-linking, then to assess which sclera is closer to human sclera.SETTING:Department of Ophthalmology, Shandong Provincial Hospital affiliated to Shandong University.DESIGN:Animal eye study.METHODS:Eight rabbits,8porcine eyeballs, and8human eyeballs were included. One rabbit eye and half of each bisected human or porcine eyeball were treated with riboflavin/UVA cross-linking (photosensitizer:0.1%riboflavin drops, UVA:3mW/cm2,365nm, and40minutes). Untreated fellow rabbit eyes and eyeball halves served as controls. A10mm×20mm sclera band was harvested from each specimen. From this band, two3.5mm×15mm strips were prepared for stress-strain biomechanical testing. Testing consisted of examining ultimate stress, stress, and Young’s modulus at4%,6%, and8%strain.RESULTS:1、Young’s modulus(E), a measure of a tissue’s elastic properties, at8%strain was2.88±1.55×106Pa,4.46±4.09×106Pa, and14.31±8.56×106Pa in untreated porcine, rabbit, and human sclera, respectively. The stress was231.6±112×103Pa,359.1±305.3×103Pa, and1078.8±645.8×103Pa in untreated porcine, rabbit, and human sclera, respectively. Values of stress and Young’s modulus showed that human sclera was about4times stiffer than porcine sclera and about3times stiffer than rabbit sclera.2、In rabbit sclera, both the stress and Young’s modulus were significantly increased by riboflavin/UVA cross-linking(p<0.05). In porcine sclera, only the ultimate stress was significantly increased by the cross-linking treatment(p<0.05). The biomechanical properties of human sclera were not statistically affected by cross-linking(p>0.05). CONCLUSIONS:1、Human sclera has a higher biomechanical stiffness than both porcine and rabbit sclera.2、With the same irradiation dose, riboflavin/UVA cross-linking increases the biomechanical stiffness of rabbit sclera, but not porcine or human sclera.3、Compared with rabbit sclera, porcine sclera is closer to human sclera in riboflavin/UVA cross-linking for scleral stress-strain biomechanical studies.