Temperature induced tissue deformation monitored by dynamic speckle interferometry

Photocoagulation is a common retinal laser treatment. Intra- and inter-individual variations of light scattering and absorption conditions make it impossible to achieve lesions of equal strength without a real-time temperature control. An optical temperature control concept may be based on laser speckle analysis, which is investigated in this work. A HeNe laser (633nm) was used for illumination of the porcine RPE and RPE models heated by a standard coagulation laser (532nm) using different irradiances. The scattered light was imaged on a CCD camera and then analyzed regarding speckle movement. It could be demonstrated that the speckle movement is radial towards the center of heating and accordingly reverse during relaxation. Furthermore a correlation between the magnitude of movement and the irradiance could be shown.