Automatic irradiation control by an optical feedback technique for selective retina treatment {(SRT)} in a rabbit model

Selective Retina Therapy (SRT) targets the Retinal Pigment Epithelium\n(RPE) without effecting neighboring layers as the photoreceptors\nor the choroid. SRT related RPE defects are ophthalmoscopically invisible.\nOwing to this invisibility and the variation of the threshold radiant\nexposure for RPE damage the treating physician does not know whether\nthe treatment was successful or not. Thus measurement techniques\nenabling a correct dosing are a demanded element in SRT devices.\nThe acquired signal can be used for monitoring or automatic irradiation\ncontrol. Existing monitoring techniques are based on the detection\nof micro-bubbles. These bubbles are the origin of RPE cell damage\nfor pulse durations in the ns and ?�s time regime 5?�s. The detection\ncan be performed by optical or acoustical approaches. Monitoring\nbased on an acoustical approach has already been used to study the\nbeneficial effects of SRT on diabetic macula edema and central serous\nretinopathy. We have developed a first real time feedback technique\nable to detect micro-bubble induced characteristics in the backscattered\nlaser light fast enough to cease the laser irradiation within a burst.\nTherefore the laser energy within a burst of at most 30 pulses is\nincreased linearly with every pulse. The laser irradiation is ceased\nas soon as micro-bubbles are detected. With this automatic approach\nit was possible to observe invisible lesions, an intact photoreceptor\nlayer and a reconstruction of the RPE within one week.