Abstract: It is disclosed here that nucleic acid-based agents can be delivered to the brain of a human or non-human animal having a leakage in the blood brain barrier by administering the agents through the eye. Brain tissues and cells can be imaged in vivo (e.g., by magnetic resonance imaging) by linking a contrast agent to a targeting nucleic acid that can hybridize to a target nucleic acid located at the brain site to be imaged and administering the contrast agentltargeting nucleic acid conjugate through the eye. Similarly, a nucleic acid based drug (e.g., as an antisense nucleic acid or a therapeutic agent linked to a targeting nucleic acid that can hybridize to a target nucleic located at a disease site in the brain) can be administered through the eye to treat a brain disease.