Multimodal photoacoustic microscopy and optical coherence tomography imaging of damaged choroidal vessels in the rabbit retina

Photoacoustic microscopy (PAM) is a non-invasive and hybrid optical imaging technique that has a potential to visualize chorioretinal vasculature in vivo. The capability of PAM can be extended to better visualize the dynamic changes of the vasculature network in the retina when it is combined with another imaging modality such as fluorescence microscopy or OCT. In this study, an integrated PAM and OCT has been developed to identify the local tissue damage during laserinduced photocoagulation on major choroidal vessels. Choroidal lesion was induced using a high power green light laser at 532 nm with millisecond pulse duration in eight New Zealand rabbits. Each rabbit eye was irradiated for 0.5 s at a laser power of 750 mW and spot size of 100 μm. Six laser burn positions were created on each eye. At each laser burn, twenty shots of the laser were applied. Multimodal PAM, OCT, fundus, and FA were used to monitor thermal lesion at different time points (days 0, 1, 3, 5, 7, 14, 21, and 28) after photocoagulation. All thermal lesions were clearly identified with high resolution using PAM. In addition, the PAM images exhibited dynamic changes of density and morphology of choroidal vasculature. The OCT images provided visualization of the cross-sectional structure of retinal tissues and the location of thermal lesion. Multimodal PAM and OCT can provide a feasible tool for evaluation and monitoring of damaged tissues and the microvasculature of the retina.