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A. Boretsky, B. Bell, M. Motamedi, E. van Kuijk; Comparison of Subthreshold Laser Tissue Interaction Using Fundus Autofluorescence in Rats and Human. Invest. Ophthalmol. Vis. Sci. 2010;51(13):302.
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Assessment of fundus autofluorescence is now a more prevalent method used for phenotyping of inherited retinal disease. Fluorescence imaging may provide a highly sensitive method for non-invasive quantitative assessment of laser-induced lesions in the retina. Changes in autofluorescence of fluorophores in the retinal pigment epithelium (RPE) can be monitored following laser irradiation as function of exposure parameters in rats and humans.
Retired female breeding stock Brown-Norway rats were purchased at an approximate age of 6 months. A modified Heidelberg Retina Angiograph (HRA I) was used to obtain images of the fundus by either infrared (IR) reflectance or autofluorescence using excitation wavelengths of 488 and 514 nm. A LaserTek Model 41 AK laser operating from 488-514nm in conjunction with a Zeiss Model 30 SL-M slit lamp was used to deliver laser radiation and induce lesions. Various powers ranging from 10-40mW were used to obtain both suprathreshold and subthreshold lesions. Subthreshold is defined as a laser application that does not cause any minimal visible lesion (MVL). A patient underwent subthreshold focal laser treatment for drusen and the changes were followed with time. The lesions were imaged immediately post-irradiation and weekly or every monthly for rats and human respectively for an extended period of time
Individual lesions, both suprathreshold and subthreshold, were easily visualized immediately following laser treatment using HRA I in 488 and 514 autofluorescence mode. In fluorescence mode laser lesions appear as spots with reduced fluorescence relative to a broadly fluorescent background. In contrast, the same lesions visible by fluorescence were difficult to visualize in IR reflectance mode. Animals followed on a weekly basis reveal dynamic changes that begin with decreased autofluorescence immediately after laser treatment to increased autofluorescence at five weeks follow up. Similar changes took place in the patient over an extended period of time of several years.
Autofluorescence imaging of retina shows that alterations to the RPE occur at laser powers below those that cause minimal visible lesions. This technique potentially offers a highly sensitive means of assessing the influence of exposure parameters on laser-induced lesions in the retina. The changes with time occur at a different rate but are otherwise similar in rats and humans.
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