Prototype-Guided Promptable Retinal Lesion Segmentation from Coarse Annotations

Accurate segmentation of retinal lesions is critical for the diagnosis and management of ophthalmic diseases, but pixel-level annotation is labor-intensive and demanding in clinical scenarios. To address this, we introduce a promptable segmentation approach based on prototype learning that enables precise retinal lesion segmentation from low-cost, coarse annotations. Our framework treats clinician-provided coarse masks (such as ellipses) as prompts to guide the extraction and refinement of lesion and background feature prototypes. A lightweight U-Net backbone fuses image content with spatial priors, while a superpixel-guided prototype weighting module is employed to mitigate background interference within coarse prompts. We simulate coarse prompts from fine-grained masks to train the model, and extensively validate our method across three datasets (IDRiD, DDR, and a private clinical set) with a range of annotation coarseness levels. Experimental results demonstrate that our prototype-based model significantly outperforms fully supervised and non-prototypical promptable baselines, achieving more accurate and robust segmentation, particularly for challenging and variable lesions. The approach exhibits excellent adaptability to unseen data distributions and lesion types, maintaining stable performance even under highly coarse prompts. This work highlights the potential of prompt-driven, prototype-based solutions for efficient and reliable medical image segmentation in practical clinical settings.