tunnel vision 
noun [mass noun]
1Defective sight in which objects cannot be properly seen if not close to the centre of the field of view.My biggest shock was I couldn't see properly, I had very blurred tunnel vision, and worse than that, I couldn't speak....
- Night blindness develops, usually in childhood, followed by loss of peripheral visual field, progressing over many years to tunnel vision and finally blindness.
- Now ultra-stubborn influences have subsided, symptoms of tunnel vision begin to dissipate.
1.1 informal The tendency to focus exclusively on a single or limited objective or view: she has tunnel vision in all matters of opinion and morality...
- While I understand that you are a more experienced writer, the tendency for this tunnel vision is a human one.
- A teacher, whether brutally domineering or gently insistent, is still capable of suffering tunnel vision, a limited perspective of which he or she may be quite unaware.
- They can suffer from terminal enthusiasm for their subject, with the complication of single-mindedness bordering on tunnel vision.