Which defining feature is mainly different between hard and soft drusen?

The defining feature that distinguishes hard drusen from soft drusen is primarily the size and demarcation. Hard drusen are smaller, usually pinpoint in size, and appear well-defined with a clear border. In contrast, soft drusen are larger, can vary in size, and tend to have less distinct edges, often merging together. This difference in their characteristics plays a significant role in the clinical assessment of age-related macular degeneration (AMD) and other retinal pathologies.

While other factors like location, color, and texture may also differ slightly, those differences are not as pronounced or as characteristic as the differences in size and demarcation. Therefore, the emphasis on size and the clarity of the edges effectively captures the essence of what sets hard and soft drusen apart.