Clemens Alt

Graduate Student

Lin Team

After graduating from the University of Applied Sciences in Luebeck, Germany, I joined Dr. Charles Lin at the Wellman Center for Photomedicine as a full-time research assistant. Two years into the project I decided to further my education so I joined the PhD program in the Department of Biomedical Engineering at Tufts University.

My research focuses on developing novel techniques for the selective laser treatment of retinal diseases. This work is based on the concept of selective photothermolysis, which was originally proposed by Drs. Anderson and Parrish, here at the Wellman Center for Photomedicine. It forms the basis for biomedical laser applications that utilize selective absorption of a therapeutic wavelength by an endogenous or exogenous chromophore. The retinal pigment epithelium (RPE) in the back of the eye is an ideal tissue to test the applicability of the concept of photothermolysis because it is a strongly absorbing single-cell layer in close proximity to a non-absorbing, sensitive tissue layer (the neural retina). Furthermore, the concept can be utilized for the therapeutic laser treatment of retinal diseases.

Research Interests

Several retinal diseases are currently treated with conventional laser photocoagulation with pulse duration of about 100 milliseconds. Heat diffusion during the long exposure time results in thermal coagulation of photoreceptors in addition to the targeted RPE. Selective targeting of the RPE, using microsecond short exposures that minimize heat diffusion to surrounding tissue, has been demonstrated as an attractive alternative for treatment of retinal disorders that are associated with dysfunctional RPE (such as drusen in early age-related macular degeneration, diabetic macular edema, central serous retinopathy). In our new approach to selective targeting of the RPE, we rapidly scan the focus of a continuous-wave laser across the retina so as to produce microsecond exposure at each RPE cell.

We have shown that individual RPE cells can be damaged in vivo with exposure times of up to 15 microseconds, while exposure times of 20 microseconds and longer lead to coagulation of adjacent photoreceptors. Thus, our scanner can perform both selective targeting and conventional laser photocoagulation by controlling the duration of the exposure and by adjusting the irradiation geometry.

Two distinct mechanisms have been proposed for the cause of RPE cell death during selective targeting: thermally induced cell death and cell death induced by intracellular cavitation. By monitoring the amount of backscattered light during exposure we can infer whether cells have died with or without formation of intracellular cavitation: backscattering increases if bubble formation occurs. We have found that cells die predominantly due to cavitation formation for exposure times up to 10 µs. We aim to use this backscattering technique as an online monitor for cell death in an eventual prototype device for clinical use.

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