Difference between Measure Fixation and Tunnel Vision

The technical article, THE PYRAMIDS AND PITFALLS OF PERFORMANCE MEASUREMENT, defines the two as:

Tunnel vision may be seen as undue focus on performance measures to the detriment of other areas.

Measure fixation implies behaviour and activities in order to achieve specific performance indicators which may not be effective.

They seem like the same thing, focusing on performance measures/indicators leading to unintended consequences in other areas of performance, this is if u look at the examples given in the Technical Article for the two.
Please provide explicit differences in the two.

Furthermore, It goes on to say that “Involving staff at all levels in the development and implementation of the scheme” will reduce tunnel vision and “Being flexible in the use of performance measures” will reduce the extent of measure fixation, however, since they are so much the same thing shouldn’t both of these actions reduce both of these problems related to performance measures?

If you can spare the time, differentiate sub-optimization from the two as well.