tunnel vision

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Vision in which the visual field is severely constricted, as from within a tunnel looking out.
• noun An extremely narrow point of view; narrow-mindedness.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A restricted field of vision as the result of looking through some type of object or a medical condition.
• noun figuratively To focus one's attention on one specific item or event, to the exclusion of everything else.; a one-track mind

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun visual impairment involving a loss of peripheral vision