Evolution of soft drusen in age-related macular degeneration.

The pathways by which soft drusen are formed are illustrated by representative clinical and clinicopathological cases. One type is derived from small hard drusen which first tend to aggregate into clusters and then fuse, forming larger deposits termed hard clusters. Breakdown of the hard drusen results in varying degrees of softening and confluence. These soft clusters may appear in middle age and, like the preceding hard drusen, remain a focal pathology. Soft clusters commonly lead to the atrophic form of age-related macular degeneration. Another type of soft drusen is formed from membranous debris as part of a diffuse disturbance of the retinal pigment epithelium. These membranous soft drusen first appear in the seventh decade and are commonly associated with choroidal neovascularisation.