Visual field sensitivity is measured clinically in the investigation of retinal conditions such as glaucoma. It is also the primary functional endpoint in many clinical trials in ophthalmology. Since the introduction of the gold standard visual field test, Static Automated Perimetry (SAP), over 30 years ago, a great deal more has been learned about biological changes in the retina in eye disease, particularly in the retinal ganglion cells (RGCs) from cat, primate and rodent models, with many recent studies pointing towards pre-morbid degenerative events in these cells. There is also growing psychophysical evidence of enlarged RGC receptive fields in conditions such as glaucoma, before detection of damage by SAP. This has renewed interest in the design of functional tests that are capable of detecting subtle changes in the retina in early disease, in the hope that early visual loss can be halted or even reversed. The optimum visual field test is one that is sensitive to pre-morbid biological changes in the retina with minimal measurement variability and a large measurement range. This test should be applicable to a wide range of diseases that are characterised by RGC damage.