 The damage mechanism in SRT is more a thermo-mechanical one than a purely thermal one as in conventional laser treatment due to the short-duration laser pulses in the microsecond-regime. Thus, microbubble formation around the melanosomes inside the RPE cell occurs during treatment, probably leading to disruption of the cell; this is in contrast to thermal denaturation in conventional laser photocoagulation. The formation of microbubbles around the strong absorbing melanosomes inside the RPE has been proofed as damage mechanism during irradiation of the RPE with μs laser pulses. If energy is absorbed and converted to heat the thermoelastic expansion of the absorbing medium will generate an opto-acoustic OA transient. During irradiation of RPE with μs laser pulses a classical thermoelastic transient will be emitted. Due to the formation and collapse of microbubbles around the melanosomes during a successful SRT treatment, additional OA bubble transients will be emitted. This is analogous to the emission of acoustic transients during formation and collapse of cavitation bubbles. An OA based on-line dosimetry system can differentiate between a pure thermoelastic transient in a subthreshold irradiation and OA bubble transients superimposed to the pure thermoelastic transients in case of a successful treatment irradiation. Thus, SRT can clinically be guided by this specific OA detection system. 