  The complete picture of the optical properties of resonant structures, along
with the frequency, quality factor, and line shape in the scattering spectra,
is determined by the electromagnetic field distribution patterns, which are a
kind of "fingerprint" of each resonant eigenmode. In this paper, we
simultaneously analyze the changes in the spectra and the transformation of the
field pattern during the topological transitions from a thin disk to a ring
with a gradually increasing thickness and further to a split ring. In addition,
we demonstrate characteristic optical fingerprints for well-known interference
effects such as bound states in the continuum and Fano resonances.
