| Objective: To evaluate the relationship of biomechanical of sclera afterriboflavin–ultraviolet A induced sclera collagen cross-linking on rabbit’s eyesunder different irradiation time. The time threshold value or the range of theretina damage in the management will be analyzed.Methods: Twenty four New Zealand white rabbits were randomlydivided into A, B, C three groups, and chosen the left eyes for the experimentgroup, the right eyes for the control group. After anesthesia, the bulbarconjunctiva and fascia between the medial and lateral rectus of the left eyeswere separated, and superior rectus were cut off from insertion of muscle, inorder to full exposed nose above sclera. After dropping0.1%5-phosphateriboflavin five minutes on the exposed sclera, where was respectivelyirradiated to A,B,C three groups was20minutes,30minutes,50minutes usingthe ultraviolet lamp with wavelength of370nm and a surface irradiance3.0mW/cm2.Two weeks later, full-field electroretinogram (ERG) wasmeasured. After two months, the rabbits were put to death, and then5mm×10mm sclera straps of the treated sclera and corresponding parts ofcontrol sclera were made. Biomechanical stress-strain and thickness of thesclera strips were performed, which included elastic modulus, creep rate,ultimate stress and ultimate strain. In addition, routine and sclera histologicalcontrols with optical microscope and transmission electron microscope wereperformed.Result:1Sclera transparency change in different ultraviolet A exposure timeAfter the irradiation, the transparency of sclera in A, B, C three groupsmore and more obviously. The colour of the sclera was becoming from the original porcelain to the red of choroid, and the change was more and moreclear, the area was more and more large. Sclera transparency increased withthe increase of ultraviolet irradiation time.2The influence of the different ultraviolet A irradiation time for thefull-field electroretinogram (ERG)After irradiating20min,30min and50min on the experimental eyes, ther-e was no difference (P>0.05) in a, b-wave amplitude and latencies timein dark-adapted3.0and light-adapted3.0of A, B, C groups both experime-ntal and control eyes.3The influence of the different ultraviolet A irradiation time to thethickness of the strip scleraThe thickness of sclera strip in A, B, C three groups respectivelyincreased by15.62%,12.07%and16.46%. There was statistical significancein C group.(P <0.05)4The influence of the different ultraviolet A irradiation time tobiomechanics of the strip scleraThe modulus of elasticity of sclera strips in A, B, C groups respectivelyincreased by26.31%,11.24%and33.43%, the creep rate of sclera strips in A,B, C groups respectively decreased by40.47%,29.96%and53.17%, theultimate stress of sclera strips in A, B, C groups respectively increased by12.21%,22.41%and42.05%, the ultimate strain of sclera strips in A and Cgroups respectively decreased by24.94%and38.57%. The matching t testgroup and control group for their own testing: the modulus of elasticity of Cgroup P=0.025, the creep rate of C group P=0.041, the ultimate strain of Cgroup P=0.012. There was statistical significance in C group.(P <0.05)5The influence of the different ultraviolet A irradiation time to histologyof the retina and scleraOn histology, no tissue damage was detected by light microscope. Scleracollagen fibers diameter of test eyes in A, B and C groups than control eyeswere increased by transmission electron microscopy TEM (15000×), and withthe extension of ultraviolet irradiation time the collagen fibers diameter increased gradually. The distance between the collagen fibers of test eyes inthe three groups than control eyes were increased, and with the extension ofultraviolet irradiation time the distance between the collagen fibers graduallyincreased. There was a little damage in mitochondria cristae and membrane incontrol group sclera fibroblasts, and experimental group than the control groupdamage obviously. The vacuolation and myelin figure of mitochondria, cellswelling, organelles decreased of cells were observed in the three groups,three no difference in the sclera fibroblasts damage degree between theexperimental groups.Conclusion:1During the rabbit sclera collagen cross-linking experiment induced byriboflavin-ultraviolet A, follow the ultraviolet irradiation time increased, thetransparency of sclera increased gradually, sclera collagen fiber diameterincreased gradually, sclera thickness increased gradually, and then thebiomechanical strength strengthened gradually when the thickness of thesclera is400microns and irradiation time in50minutes.2There were no side-effects on the retina when the thickness of sclerawas400microns using the ultraviolet A double diode with4.2mW/cm~2UVAat370nm and the irradiation time in50minutes. |
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