Purchase this article with an account.
Hossam Seddik Abbas, Christopher Kren, Veit Danicke, Ola Thomsen, Johann Roider, Christian Herzog, Ralf Brinkmann; An Automatic Feedback Temperature Control for Retinal Laser Treatments. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3675.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Laser photocoagulation is a standard treatment for several retinal diseases. However, coagulation spots are often very irregular due to a large variation in retinal absorption. We recently developed an optoacoustic method to determine the temperature rise in real-time at the irradiation sites. In this work, we demonstrate the potential of feedback control to attain a desired reference temperature rise (ΔT) at different irradiation sites for a predefined irradiation time.
The dynamics of the temperature rise due to the applied laser power has been mathematically modelled based on data of a set of different pig eyes. The model is used to design the proposed closed-loop feedback controller, which is computed online. The control algorithm is equipped with an automated tuning mechanism to compute the required laser power within its safety limits that fulfil a set of desired temperature increases for an irradiation time of 50 ± 8 ms. Irradiation was performed on ex-vivo porcine eyes with a modified Nd:YAG-laser (Carl Zeiss Meditec AG, Visulas 532s). A Nd:YLF-laser (Crystalaser Inc., 523 nm, 75 ns, 1 kHz) simultaneously served to excite thermoelastic pressure waves. The pressure is detected by an ultrasonic transducer embedded in the contact lens and used to calculate the temperature rise. The power of the Nd:YAG-laser can be modulated in real-time with a rate of 1 kHz.
For the conducted set of experiments, three target temperatures (ΔTref) of 40°C, 50°C and 60°C have been considered. In a total of 90 experiments, the obtained results have been evaluated. The ratio of the achieved settled values of the temperature rise to the desired references in percentage was 100.5 % ± 3.3 and the resulting irradiation time was 47.6 ± 5.4 ms. For all experiments, the laser power has not violated its predefined safety limits of [0, 60] mW. All the representative experimental results will be presented during the conference.
A feedback control scheme has been demonstrated to achieve a uniform temperature rise at different irradiation sites during retinal laser photocoagulation. The control system has the ability to respect different safety limits, which prevents emergency stop during treatment. The proposed approach will have important impact for achieving a balanced and safe retinal photocoagulation lesions at the different irradiation sites.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
This PDF is available to Subscribers Only