。
My eyes are bloodshot.
Literal
Eye [subject-が] is-in-congested-state.
充血する is a suru-verb meaning 'to become congested with blood / to become bloodshot.' In ~ている form it describes the resulting state — the eyes are currently bloodshot. 充血 literally combines 充 ('fill up') + 血 ('blood'), a typical Sino-Japanese compound that names a condition precisely.