Purpose
This study was designed to evaluate selective retina therapy (SRT)-RPE tissue reaction after SRT with 1.7 micro-second pulsed laser controlled by an automatic feedback reflectometry to avoid extended thermomechanical tissue damage.
Methods
Ten shots of SRT were performed in the right eyes of C57BL/6J mice using a Q-switched Nd:YLF laser system. SRT-treated mice received IP injection of 5-ethynyl-2'-deoxyuridine (EdU) in PBS. The mice were sacrificed at 3 hours to 14 days after treatment. Infrared (IR) and fluorescein angiographic (FA) images were taken with a confocal scanning laser ophthalmoscope (Heidelberg Retina Angiograph 2®; Heidelberg Engineering, Heidelberg, Germany). The whole mount and transverse sections were analyzed with In situ cell death detection kit, POD (Roche, Germany), Click-iT® Assay Kits (Life Technologies, Carlsbad, CA) for RPE cell proliferation, immunofluorescence (IF) staining with various antibodies. The changes of RPE cell numbers within 200 μm diameter centered at SRT site were counted at 3 hours to 14 days (n=5 at each time point). Untreated and conventional laser-treated mice were compared as negative and positive control.
Results
SRT sites were not detected with IR image but clearly detected with FA. At the SRT-treated area of the retinochoroidal tissue, only RPE cells were specifically detected with TUNEL (+) labeling. EdU (+) RPE cells were detected from 1 day after treatment, increased to 7 days and remained to 14 days. With whole mount sections, breakdown of cell-cell and expansion of RPE cells were detected by β-catenin IF staining. The number of RPE cells at SRT sites was gradually decreased to 12 hours (75.6% of baseline) and recovered to 14 days (93.4% of baseline). Up-regulated expression of Otx2 transcription factor was observed in the RPE cells located at SRT site.
Conclusions
SRT induced RPE cell death without photoreceptor cell damage. SRT-treated RPE areas were recovered with expansion and proliferation of the surrounding RPE cells.