  We investigate the relationship between shadow radii (photosphere radii) and
black hole microstructures for a static spherically symmetric black hole and
confirm their close connection. As a concrete analysis, we take the
Reissner-Nordstr$\mathrm{\ddot{o}}$m AdS black hole surrounded by perfect fluid
dark matter (RN AdS black hole surrounded by PFDM) as an example. We calculate
the Ruppeiner thermodynamic scalar curvature and shadow radius (photosphere
radius) for the specific model. On the one hand, we find that the greater
density of the perfect fluid dark matter makes black hole molecules more likely
have attractive interactions. On the other hand, we provide the support to our
general investigation that the shadow radii (photosphere radii) indeed connect
the microstructures of this model.
