Injury Effect Study Of 578nm Laser On Rabbit Retina

Objective To study the injury effect of 578.2nm copper vapor laser on rabbit retina and compare the contribution of different wave length , different melanin content of the rabbit retinal and other important laser parameters such as power density, energy density in the injury effect of 578.2nm laser on rabbit retina. using the self-made laser system, under the PDT exposing way, through the retinal injury threshold of the dutch belted pigmented rabbits and New Zealand white albino rabbits and to analyze the mechanisms of laser irradiation by establishing a retinal thermal model , which was utilized for predicting temperature distribution.Methods 1. The rabbit retinal laser exposing system we established mainly consists of three parts: pulse copper vapor laser with a 578.2nm yellow outputting lights slit lamp which can be used to monitor the laser outputting power and the retinal light spot size, and observe the experiment and three dimensions and an experimental animal fixation system which is a bench and its altitude could be adjusted. Rabbit head clip and other tools were used to make the light enter into the rabbit eye safely and exactly.2. Comparison between retinal injury threshold and biological effect of 578.2nm laser on rabbit retinal : sixteen dutch belted pigmented rabbits were selected the slip lamp and was used to show the light in the rabbit eye. The power density ranged from 400 to 3000 mW/cm² with an exposure time of 100 seconds. Fundus photography, fluorescein angiography, light and electron microscopy were performed on the rabbit eyes 24h after irradiation.3.Comparison of retinal injury threshold in the rabbits: sixteen dutch belted pigmented rabbits and 12 New Zealand white albino rabbits were selected and the slip lamp was used to observe the light in the rabbit eye. The power density ranged from 800 to 3000 mW/cm² with an exposure time of 100 seconds and the retinal spot diameter was 2mm, Fundus photography and fluorescein angiography were performed on rabbit eyes 1h and 24h after irradiation.Results 1 .For the dutch belted pigmented rabbits , the MVLED₅₀ at 24h was the power density on the retina = 1621mw/cm²,the energy density on the retina = 162.1J/cm².For the New Zealand white albino rabbits, the MVLED₅₀ at 24h was the power density on the retina = 2007mw/cm²,the energy density at the retina = 200.7J/cm².2. (1) All the light spots with the power density more than 3000 mW/cm² reached grade III injury, parts of the light spots with the power density between 2000-3000 mW/cm² also reached grade IIIinjury. Some of the light spots with the power density between 1000-2000 mW/cm² reached grade II injury and others reachedgrade I injury. All the light spots with the power density under 1000 mW/cm², could not observe any injury.(2) The results found in FA lens were similar.(3)With the increasing of the laser power density, The injury of retinal layers increased with the increased laser power density.3.The result of the retinal thermal model: The highest temperature was 42℃when the power density was 600 mW/cm² and the energy density was 60 J/cm² . The highest temperature was 44.5℃when the power density was 900 mW/cm² and the energy density was 90 J/cm² . The highest temperature was 49.2℃when the power density was 1500 mW/cm² and the energy density was 150 J/cm². The highest temperature was 53.5℃when the power density was 2000 mW/cm² and the energy density was 200 J/cm² . The highest temperature was 62.5℃when the power density was 3000 mW/cm² and the energy density was 300 J/cm².Conclusions (1)The rabbit retinal laser exposing system can be used in experimental study of retinal injury. However it could not be used to measure the light spot size on the retinal. (2)The retinal power density of the same wavelength laser is the key factor. Moreover, the exposing time and retinal energy density are also the important factors. (3)The retinal laser injury threshold is lower in dutch belted pigmented rabbits than in the New Zealand white albino rabbits'.(4)The dose used in PDT for CNV will not induced thermaldamage to retinal and 578.2nm laser is more safety than 532nm laser.(5)The main biological mechanism of 578.2nm is thermal effect.(6)The retinal function maybe changed under the laser dose of less than the ED₅₀ of 578.2nm laser.