Medical device software development faces persistent challenges in portability, maintainability, and scalability particularly in vision based systems where tightly coupled, hardware specific implementations dominate. Existing architectures bind imaging pipelines directly to underlying hardware, resulting in high porting costs and resistance to modular testing. This results in significant rework during platform transitions, conflicting with the modular, independently verifiable software design advocated by standards such as IEC 62304. This work presents a modular, hybrid software architecture based on SOLID principles for medical devices, combining a layered structural decomposition with a messaging layer agnostic, event-driven inter-layer communication model. Five independently operating, process isolated layers Hardware subsystems, Image Signal Processing, Database, GUI, and Business Logic are initialised through a Configuration Layer and communicate exclusively through a lightweight asynchronous message bus, enforcing low coupling and enabling runtime reconfigurability without service interruption. The architecture serves as a general architectural framework applicable across medical device software systems, validated through a vision based imaging pipeline on heterogeneous edge platforms. Runtime reconfiguration of the ISP pipeline topology is demonstrated without disruption to adjacent layers, and the GUI layer is deployed on an architecturally distinct platform with zero source code modification, validating process-level isolation and portability. The pipeline delivers 60 FPS with zero frame loss in standard operating mode across resource differentiated hardware configurations. Cross-system reuse was validated with four of five layers requiring zero modification for a clinically distinct second system.