| Any light intensity and illumination time are over light tolerance of the retina, which will cause light damage of the retina. The retina is an important organizational structure of visual organs and vulnerable to light injury. Refracting media in eyes has a strong focusing effect and canconverges incident beam into a tiny optical spot, which renders light intensity reaching the retina per unit area is 105 times of that reaching the corneal. In the early 17th century, Swiss doctor Bonetus described that visual impairment was caused by sunlight. In 1966, Noell. et.al. reported that a certain amount of light, even lower than the threshold of thermal injury, led to retinal injury of mouse subjects. It prones to suffer from light injury of the retina without special protection when exposed under strong sunlight(intensity to be 130000lux), especially in the high mountains, deserts, islands and the ship deck and other environments which enhance the light radiation effect. Lower illumination of visible light(from fluorescent lamp, operating microscope) usually adopted to create light injury by exposing for a long time in previous experiments. In this experiment, light injury was caused by light from xenon lamp close to spectrum of sunlight, 30000 lux, stimulated daylight of cloudy day, filtered out infrared light, which did not increased temperature significantly and reduced the heat damage. Experimental conditions were close to sunlight causing retinal damage. The investigations on pathologic changes of the retina are mostly centralized on the early phases after light injury. This experiment on light injury was performed to observe dynamically pathologic changes of the retina for a long time.PURPOSE:25 healthy New Zealand white rabbits were randomly divided into three groups. Rabbit eyes were exposed to 30000 lux simulated solar about 15 min and 30 min, respectively. After exposure, rabbits retinal were obtained at various times for light microscope and transmission electron microscopy examination, and apoptosis rates of retinal photoreceptor cells were detected. To investigate the effect and light injury mechanism of rabbit retinal organizational structure by simulating short-term exposure to intense solar exposure.METHODS:1,AnimalsSelect 25 similar months old and healthy adult rabbits, of either sex, weight 2 ~ 2.5 kg. Animals were randomly divided into three groups. The control group includes 5 rabbits, 15 min illumination group 5 rabbits and 30 min illumination Group 15 rabbits. Animal indoor relative humidity was maintained a range of 40%~60%, the indoor temperature range of 21 ~ 24℃. All experimental rabbits were kept for 7d in natural cyclic light-dark (12 hours light; 12 hours dark)to adapt environment and 24h the light-dark adaptation before intense light exposure.2,Establishment of a model of light injuryThe pupils Of rabbit were dilated by compound tropicamide to 8mm. Rabbits of light exposure group were fixed (only rabbit head exposed). Rabbits eyes was put eye speculum and exposed under xenon light which filtered out infrared and light intensity was 30000 lux. Rabbits based on different groups were treated by light exposure for 15 min and 30 min, respectively; then rabbits were returned to animal room after 30 min of dark adaptation and reared under normal conditions. Specimens of rabbits from 15min light exposure group were separated for examination after 2d, and specimens from 30min light exposure group taken after 2d, 7d, and 14d. The unexposed group was reared normally after mydriasis as the control and specimens were separated after 2d for examination.3,Optical Microscope ExaminationEyeballs of experimental animals were enucleated under general anesthesia, removed anterior segment, and fixed in a 10% Formalin solution 10% for 48h. Based on sagittal plane, specimens were obtained at l PD from the optic nerve root temporal side, paraffin-embedded, prepared serial sections of 5μm, stained routinely by HE and TUNEL labeling, and examined under optical microscope.4,Transmission Electron Microscopy(TEM)Examination Eyeballs of experimental animals were enucleated under general anesthesia, removed anterior segment, and fixed in a 2% formaldehydum polymerisatum -2.5% glutaraldehyde solution of 4℃for 2h. Specimens were obtained at l PD from the optic nerve root temporal side, cut into rectangle tissue mass(1mmX0.5mm), washed 3 times by using dimethyl arsenic sodium buffer (pH 7.2), fixed in 1% osmium acid of 4℃, dehydrated step by step, and embedded directionally. Semi-thin section was located to prepare ultrathin section, double stained in uranyl acetate and lead citrate and observed with TEM.5,Detection of Retinal ApoptosisSelecting randomly 5 vision fields on TUNEL labeled section at posterior pole of retina, counting the total number of photoreceptor cells and positive coloring of the apoptosis photoreceptor cell, and calculating apoptosis rate of photoreceptor cells with average values6,Statistical Data AnalysisData were recorded by Microsoft Office Excel software, and group comparison were analyzed for statistical significance by t-test statistics using SPSS 13.0 for Windows software. Data were expressed as means±SE, when p < 0.05 the results were accepted as statistically significant.RESULTS:1,Optical Microscope ExaminationThere were no obvious pathological changes in normal retinal tissues, which were integral and clear structure. Examination results of 15min light exposure group at 2d: organizational structure between the rod and the cone of retina was disorder and no no obviously bouncary; nucleus in outer nuclear layer displayed chaotic arrangement, and extracellular edema observed; nucleus in internal granular layer was disorder arrangement, and nucleus in ganglionic layer were disappeared occasionally, and the cytoplasm was vacuolated. Examination results of 30min light exposure group at 2d: organizational structure between the rod and the cone of retina was disorder, no obviously bouncary, and even broken tissue; nucleus in outer nuclear layer displayed chaotic arrangement, extracellular edema increased in amount; nucleus in internal granular layer was disorder arrangement, disappeared nucleus, and vacuolated cytoplasm; Examination results of 30min light exposure group at 7d: majority of organizational structure between the rod and the cone of retina was ruptured ; nucleus in outer nuclear layer displayed chaotic arrangement, some disappeared nucleus, and vacuolated cytoplasm; most nucleus in ganglionic layer were disappeared and vacuolated. Examination results of 30min light exposure group at 14d: organizational structure between the rod and the cone of retina was arranged more orderly, and ruptured tissue recovered obviously; nucleus in outer nuclear layer displayed order arrangement, vacuolated occasionally; nucleus in internal granular layer was more regular arrangement; some nucleus in ganglionic layer were disappeared, and vacuolated cytoplasm.2,TEM ExaminationRetinal structures of animals in control group were almost normal. Examination results of 15min light exposure group at 2d: membrane structure of outer segment between the rod and the cone are disorder and discrete lamellar structure; mitochondrial of the inner segment were swollen and individual ridges were ruptured; cell plasm of external granular layer was vacuolated-like; cell plasm of internal granular layer was swollen mildly; cell morphology of ganglionic layer was almost normal. Examination results of 30min light exposure group at 2d: membrane structure of outer segment between the rod and the cone are disorder and dispersed severely; mitochondrias of the inner segment were swollen and ridges were ruptured; cell plasm of external granular layer was vacuolated-like; cell plasm of internal granular layer was swollen mildly; cell plasm of ganglionic layer was swollen mildly. Examination results of 30min light exposure group at 7d: membrane structure of outer segment between the rod and the cone are disorder, and lamellar structure was disappeared and vacuolated; mitochondrias of the inner segment were swollen and ridges were ruptured; cell plasm of external granular layer was swollen, vacuolated largely, and disordered; partial membranes were damaged; cell plasm of internal granular layer was swollen severely, vacuolated-like, and partial membranes were damaged; cell plasm in ganglionic layer was swollen and membrane was damaged. Examination results of 30min light exposure group at 14d: membrane structure of outer segment between the rod and the cone are regularly arranged, and lamellar structure was more compact ; mitochondrias of the inner segment were swollen and ridges were ruptured; swollen cell plasm of external granular layer was mitigatory and arranged more regularly; swollen cell plasm of internal granular layer was reduced and arranged more orderly; cell plasm of ganglionic layer swelled lightly.3,Detection of Retinal ApoptosisNormal retinal TUNEL stained were negative. In external granular layer of light exposure groups, dispersed positive cells can be seen, which show granular yellow or brown and was located in the nucleus. Partial brink of nucleus was heavily stained and lightly in central, referring to a ring appearance . For 15min light exposure group at 2d, apoptosis rate of photoreceptor cells was 13.23%±0.86%, and 13.26%±1.54% for 30min light exposure group at 2d, 29.54%±1.44% for 30min light exposure group at 7d, and 29.21%±0.99% for 30min light exposure group at 14d, respectively.CONCLUSIONS:1,In this experiment, light injury was caused by light from xenon lamp close to spectrum of sunlight, 30000 lux, stimulated daylight of cloudy day, filtered out infrared light, which did not increased temperature significantly and reduced the heat damage. Experimental conditions were close to sunlight causing retinal damage. The model was successful founded.2,The pathologic changes of retina can be observed at 2d after 30000 lux sunlight-simulated exposure for 15min, which provided the evidence that light damage of rabbit retinal can be happened after short time highlight exposure.3,The investigations on pathologic changes of the retina are mostly centralized on the early phases after light injury. This experiment on light injury was performed to observe dynamically pathologic changes of the retina for a long time. The results show organizational damage of the retina experienced a process from non-acute and aggravating injury to recovering gradually injury.
|
PDF Full Text Request