Modulation of inflammatory processes by thermal stimulating and RPE regenerative laser therapies in age related macular degeneration mouse models

Real-Time Temperature-Controlled Retinal Laser Irradiation in Rabbits

Purpose

Subdamaging thermal retinal laser therapy has the potential to induce regenerative stimuli in retinal diseases, but validated dosimetry is missing. Real-time optoacoustic temperature determination and control could close this gap. This study investigates a first in vivo application.

Methods

Two iterations of a control module that were optically coupled in between a continuous-wave commercial laser source and a commercial slit lamp were evaluated on chinchilla rabbits. The module allows extraction of the temperature rise in real time and can control the power of the therapy laser such that a predefined temperature rise at the retina is quickly achieved and held constant. Irradiations with aim temperatures from 45°C to 69°C were performed on a diameter of 200 µm and a heating time of 100 ms.

Results

We analyzed 424 temperature-guided irradiations in nine eyes of five rabbits. The mean difference between the measured and aim temperature was -0.04°C ± 0.98°C. The following ED50 values for visibility thresholds could be determined: 58.6°C for funduscopic visibility, 57.7°C for fluorescein angiography, and 57.0°C for OCT. In all measurements, the correlation of tissue effect was higher to the temperature than to the average heating laser power used.

Conclusions

The system was able to reliably perform temperature-guided irradiations, which allowed for better tissue effect control than simple power control. This approach could enhance the accuracy, safety, and reproducibility of thermal stimulating laser therapy.

Translational Relevance

This study is a bridge between preclinical ex vivo experiments and a pilot clinical study.

Comparative Treatment Study on Macular Edema Secondary to Branch Retinal Vein Occlusion by Intravitreal Ranibizumab with and without Selective Retina Therapy

The purpose of this study was to compare the safety and efficacy of selective retina therapy (SRT) combined with the intravitreal injection of ranibizumab (IVR) in patients with macular edema (ME) secondary to branch retinal vein occlusion (BRVO). This trial was a 12-month single-center, randomized, single-masked prospective study. Eligible patients were randomized (1:1) to IVR and SRT (IVR + SRT group), or IVR and sham SRT (IVR + sham group). After the initial IVR, all participants received ME resolution criteria-driven pro re nata treatment. SRT or sham SRT was always applied one day after IVR. The primary outcome measure of this study was the mean change in central macular thickness (CMT) from baseline, and the secondary outcome measures were the mean change in visual acuity from baseline and the number of IVR treatments at a 52-week follow-up. Thirteen patients were in the IVR + SRT group, and 11 were in the IVR + sham group. Compared to the baseline, mean CMT and BCVA improved significantly after 52 weeks in both groups, with no significant difference between the two groups. The mean number of IVR was 2.85 ± 1.52 in the IVR + SRT group and 4.73 ± 2.33 in the IVR + sham group at the 52-week follow-up, with a significant difference between the two groups (p < 0.05). IVR combined with SRT may significantly decrease the number of IVR treatments while maintaining the visual and anatomical improvement effect of IVR monotherapy.

Selective retina therapy and thermal stimulation of the retina: different regenerative properties - implications for AMD therapy

BACKGROUND

Selective Retina Therapy (SRT), a photodisruptive micropulsed laser modality that selectively destroys RPE cells followed by regeneration, and Thermal Stimulation of the Retina (TSR), a stimulative photothermal continuous wave laser modality that leads to an instant sublethal temperature increase in RPE cells, have shown therapeutic effects on Age-related Macular Degeneration (AMD) in mice. We investigate the differences between both laser modalities concerning RPE regeneration.

METHODS

For PCR array, 6 eyes of murine AMD models, apolipoprotein E and nuclear factor erythroid-derived 2- like 2 knock out mice respectively, were treated by neuroretina-sparing TSR or SRT. Untreated litter mates were controls. Eyes were enucleated either 1 or 7 days after laser treatment. For morphological analysis, porcine RPE/choroid organ cultures underwent the same laser treatment and were examined by calcein vitality staining 1 h and 1, 3 or 5 days after irradiation.

RESULTS

TSR did not induce the expression of cell-mediators connected to cell death. SRT induced necrosis associated cytokines as well as inflammation 1 but not 7 days after treatment. Morphologically, 1 h after TSR, there was no cell damage. One and 3 days after TSR, dense chromatin and cell destruction of single cells was seen. Five days after TSR, there were signs of migration and proliferation. In contrast, 1 h after SRT a defined necrotic area within the laser spot was seen. This lesion was closed over days by migration and proliferation of adjacent cells.

CONCLUSIONS

SRT induces RPE cell death, followed by regeneration within a few days. It is accompanied by necrosis induced inflammation, RPE proliferation and migration. TSR does not induce immediate RPE cell death; however, migration and mitosis can be seen a few days after laser irradiation, not accompanied by necrosis-associated inflammation. Both might be a therapeutic option for the treatment of AMD.