Programm                 "Degeneration und Regeneration– Grundlagen, Diagnostik und Therapie"

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Non-invasive On-line Temperature Determination during Laser Treatment at the Fundus of the Eye

Brinkmann R., Schüle G., Birngruber R.
Medizinisches Laserzentrum Lübeck

Purpose: Background: Almost all laser treatments at the fundus of the eye are primarily based on elevated temperatures. The temperature increase depends on the laser parameter, however, also on the individual pigmentation and the local pathology. For long irradiation times the perfusion has also to be taken into account. We present a non-invasive method to determine this temperature increase in real time during laser treatment.
Method: The determination of the temperature was performed optoacoustically by anlysing the pressure transient emitted during tissue expansion due to the laser heating. The transients were recorded with a hydrophon in vitro. Clinically for selective RPE-treatment (SRT), the contact lens was modified with an embedded ultrasonic transducer.
Results: We used used a Nd:YLF-laser (527 nm, 1.7 µs) to determine the tissue data relevant for temperature determination. Using enucleated porcine RPE-probes, we found a good correlation to temperature calculations. In patient treatment, we noticed a base temperature increase of 55°C when repetitively applying the laser pulses with 500 Hz, while it was only 5°C when using 100 Hz.
Summary: Optoacoustic methods are principally suited for non-invasively determing the temperature increase on-line during laser treatment. In the talk, we discuss possible applications for transpupillary thermal thera

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