Recently the assessment of rates of visual field change has been gaining more clinical importance rather than just identification of the disease.
The answer to this question depends somewhat on whether the deficit caused by glaucoma already covers the central part of the field of view, or prevents the fixation of sight at a given point in space in a different way.
If the patient has an intact ability of visual fixation on a given point in space, then to assess the rates of visual field change we can use the classic methods of perimetry, including static and kinetic perimetry. We can also use customable specialized software, which allows a quick and accurate assessment of the state of the field of view over a longer period of time (for example http://neurovision.nencki.gov.pl/specvis/home.html, manuscript with software validation study is in preparation - information after its publication will appear on the website given above).
On the other hand, when the patient has lost the ability to visual fixation, then we can immobilize the eyeball and "aim" it manualy for the purpose of the test with use of perimetry methods mentioned above, or we can conduct the electroretinography test, which measures electrical activity generated by the photoreceptor cells in the retina when the eye is stimulated by a special strobe light or a reversing checkerboard pattern of light (the measurement is captured by an electrode placed on the front surface of the eye - cornea - and a graphic record called an electroretinogram - ERG - is produced).
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