In almost all retinal laser treatments the therapeutic effect is initiated by a transient temperature increase. Due to differences in tissue properties and physiology like pigmentation and vascular blood flow an individually different temperature increase might occur with crucial effects on the therapeutic benefit of the treatment. In order to determine the individual retinal temperature increase during cw-laser irradiation in real-time we developed a non-invasive method based on optoacoustics. Simultaneously to the cw-laser irradiation (λ = 810 nm, P < 3 W, t = 60 s) pulses from a dye laser (λ = 500 nm, τ = 3.5 ns, Ε ≈ 5 μJ) are applied concentrically to the cw-laser spot on the eyeground. The absorption of the pulses lead to a consequent heating and thermoelastic expansion of the tissue. This causes the emission of an ultrasonic pressure wave, which amplitude was found to be temperature dependent following in good approximation a 2<sup>nd</sup> order polynomial. The pressure wave was measured by an ultrasonic transducer embedded in a contact lens placed on the cornea. The experiments were performed in-vivo on rabbits. Simultaneous measurements with a miniaturized thermocouple showed a similar slope with a maximum local deviation of 0.4 °C for a temperature increase of 5.5 °C. On two rabbits measurements pre and post mortem at the same location were performed. The temperature increase after 60 s was found to raise by 12.0 % and 66.7 % post mortem, respectively.
These data were used to calculate the influence of heat convection by blood circulation using a numerical model based on two absorbing layers and assuming a constant perfusion rate for the choriocapillaris and the choroid.
Overall the presented optoacoustic method seems feasible for a non-invasive real-time determination of cw-laser induced retinal temperature increases and might serve as a temperature based dosimetry control during retinal laser treatments.
Tumor thermo treatment such as photodynamic therapy (PDT) or transpupillary thermotherapy (TTT) deal with long term and large laser spot exposures. The induced temperature increase is not exactly known . Under these conditions convective heat transfers due to the blood flow in the choroid and the choriocapillaris must be considered in addition to the usually calculated heat conduction. From an existing analytical model defining a unique convective term for the whole fundus irradiated with Gaussian irradiance distribution lasers , we developed a numerical one allowing a precise modelling of convection and calculating heating evolution and temperature profiles of the fundus of the eye. The aim of this study is to present the modelling and several comparisons between experimental results  and numerical ones concerning the convective heat transfers inside the fundus of the eye.