We present a high-speed three-dimensional optical-resolution photoacoustic microscopy (OR-PAM) system featuring an optimized optical-acoustic combiner (OAC) and a novel, to our knowledge, curved scanning strategy. To enhance acoustic detection sensitivity, four OAC configurations were systematically evaluated. The design employing a spherically focused ultrasound transducer and a 45 degrees glass reflector achieved the highest sensitivity. To address the limited depth of focus (DOF) in conventional OR-PAM, we developed a curved scanning method that extends the DOF from 1.74 mm to similar to 10 mm. The integrated system enables high-resolution, volumetric imaging with uniform high lateral resolution over an extended DOF. Phantom and in vivo experiments, including mouse ear and brain vasculature imaging, demonstrate significantly improved structural visibility and vessel density compared to planar scanning. The compact OAC design and fiber-optic light delivery offer the potential for handheld implementation. This work establishes a sensitive, large-DOF OR-PAM platform for high-quality vascular imaging of biological tissues. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.