1.NounA restricted field of vision, especially as the result of looking through some type of object or a medical condition.
"Some people experience tunnel vision during a panic attack.; It took some time for him to get used to the tunnel vision he experienced while looking through a periscope."
2.NounThe tendency to focus one's attention on one specific idea or viewpoint, to the exclusion of everything else.
"After Mark fell victim to tunnel vision, nothing you could say to him would change his mind."