Before we get started with the individual techniques of measuring visual fields, it's important to understand some basic terms and principles. Entire books have been written about visual fields, so while this and similar articles are geared towards basic review, you may wish to check out some of the resources below to get more details.
There are relatively few causes for tunnel visual fields (or “gun barrel” visual fields), which is a relatively common finding in neuro-ophthalmology. There are 8 major categories of tunnel visual fields, which can be determined systematically through careful history and examination. This differential diagnosis is adopted from Duane’s Clinical Ophthalmology.