Abstract
Purpose :
In retinal laser treatment, the tissue effect only partially correlates to laser energy due to differences in light absorption, light scattering and retinal pigmentation. Especially in subvisible laser treatment, the therapeutic accuracy is low. Thus, treatment reliability and reproducibility are limited.
We have previously reported on real-time temperature-guided retinal laser therapy to improve reproducibility. In this study, we report on the correlation of retinal temperature and laser-tissue effect.
Methods :
A conventional 532nm continuous wave laser (Zeiss VisuLas 532) is used with a custom-build modulation module (Medical Laser Center Lübeck), which can measure the temperature rise in real-time with a rate of 3 kHz. Based on this, it controls the laser power in real-time such that a desired target temperature is quickly obtained and held for the rest of the irradiation.
Irradiations with target temperatures from 45 to 69 °C were performed in rabbits with a diameter of 200 µm and an exposure time of 100ms. With a laboratory PC-controlled module, we performed irradiations in 5 eyes of 3 rabbits. For an upcoming clinical study, it was converted to a microcontroller-based system, with which so far 1 eye of 1 rabbit was treated. Funduscopy, optical coherence tomography (OCT) and fluorescence angiography (FAG) were used for evaluation.
Results :
With the PC system, the following ED-50 values were determined: Funduscopic visibility 60.2 °C, FAG visibility 60.2 °C, OCT visibility 59.4 °C. In OCT, the greatest linear diameter (GLD) of the lesions correlated better to temperature (R2 = 0.62) than to laser power (R2 = 0.47). The aim temperature was reached with an average error of 3.5%.
With the microcontroller system, comparable results could be reproduced. The average error in aim temperature was 2.3% (97% of lesions within a maximum error of 5%). ED-50 values were comparable in FAG (61.9 °C) and slightly higher in funduscopy (68.2 °C; pilot data with small sample size).
Conclusions :
It could be shown that temperature-guided laser irradiations can improve accuracy in retinal laser therapy. Lesion strength is better correlated to temperature than to bare laser power. We are planning to begin a clinical study for temperature-guided non-damaging laser treatment in patients with central serous chorioretinopathy in early 2022.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.